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JP2004201033

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DESCRIPTION JP2004201033
[PROBLEMS] It is possible to output a sound for the right channel and a sound for the left
channel with sufficiently reduced noise, and can be easily miniaturized. First, a first attenuator 21
halves a signal output by a first microphone 11 and a second attenuator 22 outputs a signal
output by a second microphone 12. Halve it. Next, the first adder 23 subtracts the signal output
by the first attenuator 21 from the signal output by the second attenuator 21. Next, the noise
band extraction unit 24 extracts a signal in the touch noise band from the signal output by the
first adder 23. Next, the third adder 27 adds the signal output by the first microphone 11 and the
signal output by the noise band extraction unit 24. Also, the fourth adder 28 subtracts the signal
output by the noise band extraction unit 24 from the signal output by the second microphone 12.
[Selected figure] Figure 1
Noise reduction apparatus and method
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
noise reduction device and a noise reduction method suitable for application to a microphone
device mounted on, for example, a camera-integrated recording device. 2. Description of the
Related Art For example, in a video camera such as a home digital video camera, audio recorded
on a recording medium is generally collected by a built-in stereo microphone device. The stereo
microphone device is called two microphones (hereinafter referred to as microphones). The voice
for the right channel is input to one of the microphones, and the voice for the left channel is
input to the other microphone. Then, an audio signal for the right channel and an audio signal for
the left channel are output. [0003] In recent years, due to the progress in downsizing of video
cameras, when a user performs an operation such as zooming or focusing or performs a switch
operation during imaging, the user inadvertently touches the vicinity of the microphone. Noise
(hereinafter referred to as touch noise) caused by ) Is easily input to the microphone. In addition,
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in the case where the video camera captures an image of a relatively quiet area, the sensitivity of
the microphone is increased by an internal automatic gain control circuit. If the sensitivity of the
microphone increases, even a slight touch noise will be input to the microphone. Furthermore,
although a video camera generally includes a nondirectional microphone, the nondirectional
microphone is used with a directional characteristic by performing an operation on the output of
the microphone. . Therefore, in the video camera, the noise frequency band is raised due to the
proximity effect specific to the directional characteristic, and the noise is often more noticeable
than the target audio signal. In the video camera, in order to reduce the noise described above,
the microphone unit is floated from the cabinet by an insulator such as a rubber damper or
floated in the air by a rubber wire or the like to absorb the vibration propagating in the cabinet.
And avoid vibration noise being input to the microphone. However, the method of floating the
microphone unit from the cabinet by the insulator or the rubber wire reduces the effect of
absorbing the vibration when the vibration is strong. Further, the effect of absorbing the
vibration is also reduced by the frequency of the vibration.
Conversely, when the vibration is at an inherent frequency, the microphone unit may resonate.
That is, it becomes difficult to absorb all vibrations. In addition, since it is necessary to consider
the effects of the insulator and the rubber wire, the resonance vibration of the microphone unit,
and the like, the structural design becomes difficult, which becomes a factor that hinders the
downsizing and cost reduction of the video camera. Furthermore, touch noise includes not only
vibration noise that propagates in the cabinet, but also acoustic noise that propagates as sound in
the air. That is, since the propagation path of touch noise to the microphone unit is complicated
and does not necessarily propagate in the cabinet, it is difficult to reduce the acoustic noise by
the method of floating the microphone unit from the cabinet by the insulator or the rubber wire .
For the reason described above, in the method of floating the microphone unit from the cabinet
by the insulator or the rubber wire, there is a limit to the reduction of the touch noise, and it
becomes difficult to reduce it to a level that the user can satisfy. On the other hand, the applicant
of the present application has proposed a stereo microphone device that reduces noise by an
adaptive noise canceller (ANC) method using an adaptive filter (for example, Patent Document 1).
As shown in FIG. 12, the stereo microphone device 200 has a first microphone 201 and a second
microphone 202 arranged so that the sound receiving surfaces are in the same direction, and the
sound receiving surfaces are the first. And a third microphone 203 disposed to face the sound
receiving surface of the second microphone 201 or 202. As described above, since the first to
third microphones 201 to 203 are arranged, in the stereo microphone device 200, the signal R
output by the first microphone 201 and the output by the third microphone 203 are output. The
sound signal is in phase, the vibration noise is in antiphase, and the levels are almost the same.
Further, the signal R output by the first microphone 201 and the signal L output by the second
microphone 202 are substantially the same. In the stereo microphone device 200, first, the first
adder 204 adds the signal in which the signal R is halved and the signal in which the signal L is
halved. Then, the second adder 205 subtracts the signal output by the third microphone 203
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from the signal output by the first adder 204, whereby vibration noise included in the signals R
and L is obtained. It extracts and supplies to the adaptive filter 206.
Next, the adaptive filter 206 performs an adaptation process on the supplied vibration noise to
generate a pseudo noise Y having a correlation with the vibration noise. The adaptive filter 206
supplies the pseudo noise Y to the third adder 207 and the fourth adder 208. Then, the third
adder 207 subtracts the pseudo noise Y from the signal R to generate an audio signal of the right
channel with reduced noise. The fourth adder 208 subtracts the pseudo noise Y from the signal L
to generate a noise-reduced audio signal of the left channel. As described above, in the stereo
microphone device 200, the pseudo noise Y is generated by the adaptive filter 206, and The third
adder 207 subtracts the pseudo noise Y from the signal R, and the fourth adder 208 subtracts
the pseudo noise Y from the signal L, so that it is possible to output an audio signal with reduced
noise. Become. However, in the stereo microphone device 200, three of the first microphone 201,
the second microphone 202, and the third microphone 203 are used to output an audio signal
for the right channel and an audio signal for the left channel. Need to have two microphones.
That is, in order to output the audio signal for the right channel and the audio signal for the left
channel, the stereo microphone device 200 needs to have many microphones. Therefore, it
becomes difficult to miniaturize the stereo microphone device 200. Further, when the stereo
microphone device 200 is mounted on a video camera, it becomes difficult to miniaturize the
video camera. Further, in the stereo microphone device 200, one pseudo noise Y is generated,
and a signal for right channel is generated by subtracting the pseudo noise Y from the signal R,
and the pseudo noise Y is generated from the signal L. A signal for the left channel is generated
by subtraction. Therefore, when there is a phase difference or level difference between the noise
contained in the signal L and the noise contained in the signal R, the noise can not be accurately
reduced. Further, in the stereo microphone device 200, since one adaptive filter is used to
generate the pseudo noise Y, the number of taps of the adaptive filter 206 is increased, which
requires time for convergence. In addition, when the acoustic noise characteristic and the
vibration noise characteristic are different, it is difficult to sufficiently reduce the noise.
The present invention has been proposed in view of the above-described conventional situation,
and is a noise reduction device which is easy to miniaturize and can sufficiently reduce vibration
noise and acoustic noise. And provide a method. According to the noise reduction device of the
present invention, the first omnidirectional microphone is arranged such that the sound receiving
surface is in a predetermined direction, and the sound receiving surface is The first
nondirectional microphone has a direction different from the direction of the receiving surface of
the first nondirectional microphone by 180 ░, and is disposed such that the distance from the
first nondirectional microphone to the receiving surface is a predetermined interval. A second
microphone and a difference signal that is 1/2 the level of a signal obtained by subtracting the
signal output by the first nondirectional microphone from the signal output by the second
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nondirectional microphone is generated Difference signal generation means, first calculation
means for adding the signal output by the first nondirectional microphone and the difference
signal, and output by the second nondirectional microphone And second operation means for
subtracting the difference signal from the input signal. In the noise reduction device according to
the present invention, the first nondirectional microphone is disposed such that the sound
receiving surface is in a predetermined direction, and the sound receiving surface is the first
nondirectional property. A second nondirectional microphone arranged in a direction different by
180 ░ with respect to the direction of the receiving surface of the microphone and at a
predetermined distance from the receiving surface of the first nondirectional microphone. And a
sum signal for generating a sum signal that is 1/2 times the level of the signal obtained by
adding the signal output by the first nondirectional microphone and the signal output by the
second nondirectional microphone Generation means, first operation means for subtracting the
sum signal from the signal output by the first nondirectional microphone, and the signal output
by the second nondirectional microphone A second operation means for subtracting the sum
signal; a first adaptive control means for adaptively controlling the signal output by the first
operation means to generate a first pseudo noise signal; A second adaptive control means for
adaptively controlling a signal output by the second arithmetic means to generate a second
pseudo noise signal; and a signal output from the first nondirectional microphone from the first
adaptive control means. , And fourth operation means for subtracting the second adaptive control
signal from the signal output by the second non-directional microphone; The adaptive control
means adaptively controls the signal output by the first arithmetic means based on the output
from the third arithmetic means, and the second adaptive control means controls the fourth
arithmetic means. Based on the output from the means Characterized in that it adaptively
controls signal output by said second calculating means.
In the noise reduction method according to the present invention, a first nondirectional
microphone arranged so that the sound receiving surface is in a predetermined direction, and a
sound receiving surface of the first nondirectional microphone A second nondirectional
microphone arranged in a direction different by 180 ░ with respect to the direction of the sound
receiving surface, and arranged at a predetermined distance from the sound receiving surface of
the first nondirectional microphone; It is a noise reduction method in a stereo microphone device
provided, wherein the level of a signal obtained by subtracting the signal output by the first
nondirectional microphone from the signal output by the second nondirectional microphone is
half the level of the signal A difference signal generating step of generating a difference signal
which is the first signal processing step of generating a difference signal, and a first operation
step of adding the signal output by the first nondirectional And flop, characterized in that it
comprises a second arithmetic step of subtracting the difference signal from the signal output by
the second omni-directional microphones. Further, in the noise reduction method according to
the present invention, the first nondirectional microphone is disposed such that the sound
receiving surface is in a predetermined direction, and the sound receiving surface includes the
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first nondirectional property. A second nondirectional microphone arranged in a direction
different by 180 ░ with respect to the direction of the receiving surface of the microphone and
at a predetermined distance from the receiving surface of the first nondirectional microphone. A
method of reducing noise in a stereo microphone device comprising: a sum signal obtained by
adding a signal output by the first nondirectional microphone and a signal output by the second
nondirectional microphone; A sum signal generation step of generating by doubling and a first
operation step of subtracting the sum signal from the signal output by the first nondirectional
microphone and outputting the result. And a second operation step of subtracting the sum signal
from the signal output by the second nondirectional microphone and outputting the signal
output in the first operation step. A first adaptive control step of generating a first pseudo noise
signal; and a second adaptive control step of generating a second pseudo noise signal that
adaptively controls the signal output in the second calculation step. A third operation step of
subtracting the first pseudo noise signal from the signal output by the first nondirectional
microphone, and the second operation signal from the signal output by the second nondirectional
microphone And a fourth operation step of subtracting the pseudo noise signal, and in the first
adaptive control step, the first operation is performed based on the signal output in the third
operation step. The signal output in the step is adaptively controlled, and in the second adaptive
control step, the signal output in the second calculation step is adaptively controlled based on the
output from the fourth calculation means It is characterized by
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present
invention will be described in detail with reference to the drawings. First Embodiment First, a
first embodiment of the present invention will be described. As shown in FIG. 1, a stereo
microphone device 10 to which the present invention is applied includes a first microphone
(hereinafter referred to as a microphone) 11 and a second microphone 12 for converting sound
into an electrical signal and outputting it. A first amplifier 13 for amplifying a signal output by
the first microphone 11, a second amplifier 14 for amplifying a signal output by the second
microphone 12, and a signal output by the first amplifier 13 Is analog-to-digital conversion
(hereinafter referred to as A / D conversion). ), A second A / D converter 16 for A / D converting
the signal output by the second amplifier 14, a first A / D converter 15, and A noise reduction
processing unit 17 that reduces noise contained in the signal output by the second A / D
converter 16 and a calculation performed on the signal output by the noise reduction processing
unit 17 A directional calculation processing unit 18 for generating an audio signal and an audio
signal for the left channel is provided. The stereo microphone device 10 is mounted on an
electronic device such as a video camera, for example, and collects audio to be recorded on a
recording medium such as a video tape or a disc-shaped recording medium. The first microphone
11 and the second microphone 12 are nondirectional microphones. The first microphone 11 and
the second microphone 12 convert the inputted sound waves into electrical signals. As shown in
FIGS. 2A and 2C, the first microphone 11 and the second microphone 12 are provided coaxially
so that the sound receiving surfaces face each other. The first microphone 11 includes a +
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terminal 11a and a-terminal 11b, the + terminal 11a is connected to the first amplifier 13, and
the-terminal 11b is grounded. Further, the second microphone 12 includes a + terminal 12 a and
a ? terminal 12 b, the + terminal 12 a is connected to the second amplifier 14, and the ?
terminal 12 b is grounded. When the first microphone 11 and the second microphone 12 are
provided such that their respective sound receiving surfaces face each other, the diaphragms 11
c and 12 c are shown in FIG. As shown in A), the voice signals Rs and Ls that are in phase and
vibrate in opposite directions with substantially the same phase are output.
Specifically, assuming that the first microphone 11 outputs the signal indicated by the solid line
in the left diagram of FIG. 2B when the diaphragms 11 c and 12 c vibrate as indicated by the
solid line, the second The microphone 12 outputs a signal shown by a solid line in the right
figure of FIG. 2 (B). Also, when the diaphragms 11c and 12c vibrate as shown by the broken line,
the first microphone 11 outputs a signal shown by the broken line in the left figure of FIG. 2B,
and the second microphone 12 B) Output a signal shown by a broken line in the right figure. On
the other hand, when an object comes in contact with the electronic device on which the stereo
microphone device 10 is mounted, touch noise including acoustic noise and vibration noise is
generated. When an object contacts the electronic device, for example, when vibration is
generated in the direction indicated by the arrow A, the diaphragms 11c and 12c vibrate in the
same direction as indicated by a solid line or a broken line in FIG. The first microphone 11 and
the second microphone 12 output vibration noises Rn and Ln which are in opposite phase to
each other. Specifically, assuming that the first microphone 11 outputs the signal indicated by
the solid line in the left diagram of FIG. 2D when the diaphragms 11 c and 12 c vibrate as
indicated by the solid line, the second The microphone 12 outputs a signal indicated by a solid
line in the right of FIG. 2D. Also, when the diaphragms 11c and 12c vibrate as shown by the
broken line, the first microphone 11 outputs a signal shown by the broken line in the left figure
of FIG. 2D, and the second microphone 12 D) Output a signal indicated by a broken line in the
right figure. When the vibration occurs in the direction indicated by the arrow B orthogonal to
the arrow A, the diaphragms 11 c and 12 c do not vibrate, and the first microphone 11 and the
second microphone 12 do not output a signal. . Here, an interval between the first microphone
11 and the second microphone 12 (hereinafter, referred to as a microphone interval. The
relationship between the phase difference and the level difference between the signal d) and the
signal R (= Rs + Rn) output by the first microphone 11 and the signal L (= Ls + Ln) output by the
second microphone 12 will be described. Do. First, the relationship between the microphone
interval d and the phase difference between the signal R and the signal L will be described. When
a sound wave of amplitude a outputted by the sound source A is input to the first microphone 11
and the second microphone 12, the distance between the sound source A and the first
microphone 11 or the second microphone 12 is a microphone If it is sufficiently larger than the
interval d, it is considered that the sound waves output by the sound source A are input
substantially parallel to the first microphone 11 and the second microphone 12 as shown in FIG.
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Further, if the microphone distance d is sufficiently smaller than the wavelength ? of the sound
wave output by the sound source A, Expression 1 and Expression 2 shown below hold. Signal R =
a и cos (?t) Equation 1 Signal L = a и cos (?t??) Equation 2 where ? represents an angular
velocity at which the sound travels through the air, ? indicates the distance between the second
microphone 12 and the point c where the straight line connecting the second microphone 12 and
the sound source A intersects with the perpendicular drawn from the first microphone 11 at the
straight line. That is, the phase difference between the sound input to the first microphone 11
and the sound input to the second microphone 12 is ?. Therefore, compared with the signal R
output by the first microphone 11, the signal L output by the second microphone 12 is a signal
shifted by a phase difference ? based on the delay due to the microphone interval d. Become.
Next, the relationship between the microphone interval d and the level difference between the
signal R and the signal L will be described. Speech is known to propagate in the air as
compression waves, but the maximum positive value (or the minimum negative value) of speech
is dense, and the minimum (or the maximum positive value) of speech is sparse. Then, when d>
? / 2, the sound wave reaching the second microphone 12 is output by the second microphone
12 in order to reach a level falling by becoming a shadow of the first microphone 11. The
amplitude of the signal is smaller than the amplitude of the sound output by the first microphone
11. However, when d ? ? / 2, the sound input to the second microphone 12 is output by the
first microphone 11 because it is hardly affected by the sound input to the first microphone 11.
And the amplitude of the signal output by the second microphone 12 are substantially the same.
As an example, when the microphone distance d is 15 mm, the frequency F with a half cycle of
15 mm is as shown in the following Equation 3 at normal temperature. Frequency F ? sonic
speed in air / 2 d = 340/2 и 15 = 11 kHz Equation 3 Therefore, assuming that the microphone
distance d is 15 mm, the first microphone 11 and the second microphone 12 The amplitude of
the signal R output by the first microphone 11 and the amplitude of the signal L output by the
second microphone 12 become substantially the same if the frequency of the sound wave
reaching the The difference with the signal L is only the phase difference ?. If the microphone
interval d is small, the influence of the phase difference ? can be ignored.
The first microphone 11 and the second microphone 12 always have an amplitude by
determining the microphone interval d such that the band of the touch noise is equal to or lower
than the frequency F or by limiting the band of the touch noise. Outputs a signal equal to. The
noise reduction processing unit 17 outputs a signal from the first A / D converter 15 by a first
attenuator 21 that halves the signal output from the first A / D converter 15 and a second A / D
converter 16. The second attenuator 22 that halves the received signal and a first adder 23 that
subtracts the signal output by the first attenuator 21 from the signal output by the second
attenuator 22. A noise band extraction unit 24 for extracting a signal of a predetermined band
from the signal output by the first adder 23, and a first delay unit 25 to which a signal is
supplied from the first A / D converter 15. , The second delay unit 26 to which the signal is
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supplied from the second A / D converter 16, the signal output by the noise band extraction unit
24 and the signal output by the first delay unit 25 are added. And the second adder 27 that
supplies the directional calculation processing unit 18 And a third adder 28 for subtracting the
signal output from the noise band extraction unit 24 from the signal output from the first delay
unit 25 and supplying the result to the directional calculation processing unit 18. The noise band
extraction unit 24 is configured of a low pass filter (LPF), a band pass filter (BPF), and the like.
The touch noise occurs concentrated on the relatively low frequency of the signals output by the
first microphone 11 and the second microphone 12 (hereinafter, a band in which touch noise
occurs is referred to as a touch noise band). The noise band extraction unit 24 extracts and
outputs a signal of the touch noise band from the audio signal. By including the noise band
extraction unit 24, the stereo microphone device 10 can efficiently reduce touch noise. The
microphone device 10 may not include the noise band extraction unit 24. When the noise band
extraction unit 24 is not provided, the noise reduction processing unit 17 can also reduce noise
generated in a band other than the touch noise band. The first delay unit 25 controls the timing
at which the signal output by the first A / D converter 15 is supplied to the second adder 27.
Specifically, first, the first A / D converter 15 outputs a signal and supplies it to the first delay 25
and the first attenuator 21.
Next, the first delay unit 25 continues until the signal supplied to the first attenuator 21 is
supplied to the second adder 27 via the first adder 23 and the noise band extraction unit 24.
Hold the supplied signal. Then, the first delay unit 25 supplies the held signal to the second
adder 27 at the same timing as the signal is supplied from the noise band extraction unit 24 to
the second adder 27. The second delay unit 26 controls the timing at which the signal output by
the second A / D converter 16 is supplied to the + terminal of the third adder 28. More
specifically, the second A / D converter 16 outputs a signal to the second delay unit 26 and the
second attenuator 22. Next, in the second delay unit 26, the signal supplied to the second
attenuator 22 is supplied to the-terminal of the third adder 28 via the first adder 23 and the
noise band extraction unit 24. Hold the supplied signal until Then, the second delay unit 26 is
configured to hold the signal held by the third adder 28 at the same timing as the signal is
supplied from the noise band extraction unit 24 to the negative terminal of the third adder 28.
Supply to + terminal. The noise reduction processing unit 17 performs the operation described
below. First, the first attenuator 21 halves Rs + Rn output from the first A / D converter 15 to 1?2
(Rs + Rn). The second attenuator 22 halves Ls + Ln output from the second A / D converter 16 to
1?2 (Ls + Ln). Next, the first adder 23 performs an operation 1 shown below. Since Ls and Rs
have substantially the same amplitude and the same phase, Ls-Rs can be set to 0. 1/2 (Ls + Ln)1/2 (Rs + Rn) = 1/2 (Ls-Rs) + 1/2 (Ln-Rn) = 1/2 (Ln-Rn) иии Operation 1 Next, the second adder 27
performs the following operation 2. Since Ln and Rn have substantially the same amplitude and
opposite phase, Ln + Rn = 0. (Rs + Rn) + 1/2 (Ln-Rn) = Rs + 1/2 Ln + Rn-1/2 Rn = Rs + 1/2 (Ln +
Rn) = Rs Operation 2 The third adder 28 Perform operation 3 shown in. (Ls + Ln)-1/2 (Ln-Rn) =
Ls + Ln-1/2 Ln + 1/2 Rn = Ls + 1/2 (Ln + Rn) = Ls Operation 3 In the present embodiment, the
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noise band Since the extracting unit 24 is provided, the operations 2 and 3 are performed only in
the noise band, but when the noise band extracting unit 24 is not provided, the operations 2 and
3 are all bands of the audio signal. It takes place over
Next, the operation of the stereo microphone device 10 will be described. First, when voice is
input, the first microphone 11 and the second microphone 12 convert the input voice into an
electrical signal and output it. The output Rs + Rn of the first microphone 11 is supplied to the
first amplifier 13, and the output Ls + Ln of the second microphone 12 is supplied to the second
amplifier 14. Next, the first amplifier 13 amplifies the signal supplied by the first microphone 11
and supplies the amplified signal to the first A / D converter 15. Also, the second amplifier 14
amplifies the signal supplied by the second microphone 12 and supplies the amplified signal to
the second A / D converter 16. Next, the first A / D converter 15 A / D converts the signal
supplied by the first amplifier 13 and supplies it to the first attenuator 21 and the first delay
device 25. . Further, the second A / D converter 16 A / D converts the signal supplied by the
second amplifier 14 and supplies the signal to the second attenuator 22 and the second delay 26.
Next, the first attenuator 21 halves the signal supplied by the first A / D converter 15 to generate
1?2 (Rs + Rn), and the first adder Supply to the 23-terminal. In addition, the second attenuator 22
halves the signal supplied by the second A / D converter 16 to generate 1?2 (Ls + Ln), and the
positive terminal of the first adder 23 Supply to Next, the first adder 23 performs operation 1 to
generate 1?2 (L n ?R n), which is supplied to the noise band extraction unit 24. Next, the noise
band extraction unit 24 extracts a signal of the touch noise band from the signal supplied by the
first adder 23, and the second adder 27 and the third adder 28 Supply to the terminal. On the
other hand, the first delay unit 25 has the same timing as the timing at which the noise band
extraction unit 24 supplies the signal to the second adder 27 with the signal supplied by the first
A / D converter 15. , To the second adder 27. Also, the second delay unit 26 has the same timing
as the signal supplied by the second A / D converter 16 and the timing at which the noise band
extraction unit 24 supplies the signal to the-terminal of the third adder 28 To the + terminal of
the third adder 28. Next, the second adder 27 performs operation 2 to generate a signal Rs from
which the vibration noise Rn has been removed, and supplies the signal Rs to the directional
calculation processing unit 18.
The third adder 28 also performs operation 3 to generate the signal Ls from which the vibration
noise Ln is removed, and supplies the signal Ls to the directional calculation processing unit 18.
Finally, the directional calculation processing unit 18 performs an operation on the signal Rs to
generate and output an audio signal for the right channel, and performs an operation on the
signal Ls for the left channel. Generate and output an audio signal of As described above, in the
stereo microphone device 10 to which the present invention is applied, the first microphone 11
and the second microphone 12 are disposed such that the sound receiving surfaces thereof face
each other. Therefore, the audio signal Rs and the audio signal Ls have the same phase, and the
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vibration noise Rn and the vibration noise Ln have the opposite phase. That is, the audio signal
Rs and the audio signal Ls are substantially zero when subtracted, and the vibration noise Rn and
the vibration noise Ln are substantially zero. The noise reduction processing unit 17 provided in
the stereo microphone device 10 to which the present invention is applied can execute the
operations 1, 2 and 3 by the circuit configuration described above, and the audio signal Rs and
the audio signal The voice signal Rs from which the vibration noise Rn is removed and the voice
signal Ls from which the vibration noise Ln is removed are generated and output using the
relationship with Ls and the relationship between the vibration noise Rn and the vibration noise
Ln. . That is, the stereo microphone device 10 to which the present invention is applied outputs
the noise for the right channel voice and the noise for the left channel, although the number of
microphones provided is two. It is possible to Therefore, the stereo microphone device 10 to
which the present invention is applied can reduce the noise output simultaneously with the
sound for the right channel and the noise output simultaneously with the sound for the left
channel, and can be miniaturized. Is easy. Further, when the stereo microphone device 10 to
which the present invention is applied is mounted on an electronic device such as a video
camera, the mounted electronic device has noise simultaneously output with audio for the right
channel, audio for the left channel, It is possible to reduce noise that is output simultaneously,
and it becomes easy to miniaturize. Furthermore, the stereo microphone device 10 to which the
present invention is applied can sufficiently reduce noise without increasing the directional
arithmetic processing unit 18 or attaching a new A / D converter or the like. it can. Therefore, the
stereo microphone device 10 to which the present invention is applied can sufficiently reduce the
noise output simultaneously with the voice by the first microphone 11 and the second
microphone 12 at low cost without increasing the circuit size.
In the stereo microphone device 10 to which the present invention is applied, the noise reduction
processing unit 17 performs the operation 1 to output the signal Rs + Rn output from the first
microphone 11 and the second microphone 12. From the signal Ls + Ln, 1?2 (Ln?Rn) is
generated. 1/2 (Ln-Rn) is the same as the vibration noise Ln, is in reverse phase and has the
same level as the vibration noise Rn. The signal Ls is generated by subtracting 1?2 (Ln?Rn) from
the signal Ls + Ln, and the signal Rs is generated by adding the signals Rs + Rn and 1?2 (Ln?Rn).
That is, the stereo microphone device 10 to which the present invention is applied extracts
vibration noises Rn and Ln and subtracts them from the signals output by the first microphone
11 and the second microphone 12 without providing a vibration pickup microphone. The same
operation as the operation can be performed. Therefore, it is possible to avoid the problem that
the voice can not be reduced with high accuracy since the voice is input to the vibration pickup
microphone. Further, by providing the vibration pickup, it is possible to prevent difficulty in size
reduction and cost reduction. The first microphone 11 and the second microphone 12 may be
disposed so that the sound receiving surfaces face in directions different from each other by 180
░, for example, as shown in FIG. You may arrange so that a sound surface may face outside.
Further, the first microphone 11 and the second microphone 12 may not be arranged coaxially.
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By the way, the first microphone 11 and the second microphone 12 provided in the stereo
microphone device 10 have different levels of signals output when the same sound is input due
to variations in manufacturing, etc. It may not be identical. Further, the first amplifier 13 and the
second amplifier 14 have different levels of signals output when signals of the same level are
input due to variations in constants such as external resistors. There is. Furthermore, with
respect to the first A / D converter 15 and the second A / D converter 16, the levels of the signals
output when the same level signal is input may not be the same. That is, in the stereo
microphone device 10, the characteristics of the first microphone 11, the first amplifier 13, and
the first A / D converter 15, and the second microphone 12, the second amplifier 14, and the
second Of the first A / D converter 16 when the same voice is input to the first microphone 11
and the second microphone 12. The level of the signal output by 15 and the level of the signal
output by the second A / D converter 16 may differ.
Therefore, as shown in FIG. 5, in the stereo microphone device 10, the level adjustment between
the first A / D converter 15 and the second A / D converter 16 and the noise reduction
processing unit 17 is performed. Preferably, a portion 30 is provided. The level adjustment unit
30 will be described below. The level adjustment unit 30 receives the signal output from the
second A / D converter 16, the level change unit 31, the signal output from the level change unit
31, and the first A / D conversion. A level difference detection unit 32 is provided which
generates a level control signal based on the signal output by the unit 15 and supplies the
generated level control signal to the level change unit 31. The level change unit 31 amplifies or
attenuates the signal output by the second A / D converter 16 based on the level control signal
supplied by the level difference detection unit 32, and outputs the signal to reduce noise. The
signal is supplied to the unit 17 and the level difference detection unit 32. Based on the level
control signal supplied by the level difference detection unit 32, the level change unit 31 makes
the level of the signal output by itself the same as the level of the signal output by the first A / D
converter 15. The signal output by the second A / D converter 16 is amplified or attenuated and
output while changing the amplification factor or the attenuation factor. The level difference
detection unit 32 compares the level of the signal output by the first A / D converter 15 with the
level of the signal output by the level change unit 31, and based on the comparison result, the
level control is performed. A signal is generated and supplied to the level change unit 31.
Specifically, as shown in FIG. 6, the level difference detection unit 32 of the present embodiment
removes a high frequency signal from the signal output by the first A / D converter 15. A first
LPF 33, a first absolute value converting unit 34 for absoluteizing a signal output by the first LPF
33, and a first peak detecting unit for detecting a peak of the signal output by the first absolute
value converting unit 34 Peak detection unit 35, a second LPF 36 outputting a low band signal
among the signals supplied by the level change unit 31, and a second absolute value converting
the signal output by the second LPF 36 into an absolute value Second peak detection unit 38
from the signal output from the first peak detection unit 35 and the second peak detection unit
38 for detecting the peak of the signal output from the second conversion unit 37 and the
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second absolute value conversion unit 37 Exit by section 38 An adder 39 that subtracts the input
signal, a code detection unit 40 that detects the sign of the signal output by the adder 39 and
outputs a signal indicating the detection result, and a signal that is output by the code detection
unit 40 And a signal generation unit 41 that generates a level control signal based on the
The first LPF 33 and the second LPF 36 are inserted to extract a signal in a band sufficiently low
with respect to the frequency F depending on the microphone distance d shown in Equation 3.
Thus, the amplitude of the signal output by the first LPF 33 and the amplitude of the signal
output by the second LPF 36 are the same as those of the first microphone 11, the first amplifier
13, and the first A / D converter 15. And the characteristics of the second microphone 12, the
second amplifier 14, and the second A / D converter 16 except for the difference due to the
variation. The first and second peak detectors 35 and 38 detect peaks of the signals output by
the first and second absolute value converters 34 and 37. Here, peak detection will be described
in detail. First, the signal R output by the first LPF 33 has the waveform shown in the left
diagram of FIG. 7A, and the signal L output by the second LPF 36 has the waveform shown in the
left diagram of FIG. 7B. Then, the signal R output by the first absolute value conversion unit 34
has a waveform shown by the solid line in the right diagram of FIG. 7A, and the signal L output
by the second absolute value conversion unit 37 is as shown in FIG. ) The waveform shown by
the solid line in the right figure. Furthermore, the signal R output by the first peak detection unit
35 has a waveform shown by the broken line in the right diagram of FIG. 7A, and the signal L
output by the second peak detection unit 38 is FIG. 7B. It becomes the waveform shown by the
broken line in the right figure. When the processing described above is performed and the level
of the signal R is compared with the level of the signal L at time T, a delay Td depending on the
microphone distance d occurs between the signal R and the signal L. Also, it can be seen that
although there is a level difference after absolute value conversion, almost no level difference
occurs after peak detection. Therefore, the level difference after peak detection is determined by
the characteristics of the first microphone 11, the first amplifier 13, the first A / D converter 15,
the second microphone 12, the second amplifier 14, the second Most of them are attributable to
the difference from the characteristics of the A / D converter 16. The adder 39 subtracts the level
of the signal output by the second peak detection unit 38 from the level of the signal output by
the first peak detection unit 35. Therefore, the sign of the signal output from the adder 39 is
positive when the level of the signal output by the first A / D converter 15 is greater than the
level of the signal output by the second A / D converter 16 When the level of the signal output
by the first A / D converter 15 is smaller than the level of the signal output by the second A / D
converter 16, the first A / D converter 15 becomes negative. When the level of the signal output
by the second A / D converter 16 is the same, the level is 0.
The signal generation unit 41 is configured such that, based on the signal supplied by the code
detection unit 40, the level of the signal output by the level change unit 31 is the same as that of
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the signal output by the first A / D converter 15. A level control signal is supplied to the level
change unit 31 so as to be equal to the level. In the present embodiment, the signal generation
unit 41 is configured by an up / down counter. To describe the generation of the level control
signal by the signal generation unit 41 in detail, first, as shown in FIG. Next, in step S2, it is
determined whether the signal supplied from the code detection unit 40 is positive. If the sign is
not positive, the process proceeds to step S3. If the sign is positive, the process proceeds to step
S4. Next, in step S3, it is determined whether the signal supplied from the code detection unit 40
is negative. When the sign is negative, the process proceeds to step S5, and when the sign is not
negative, the process proceeds to step S6. Then, in step S4, the signal generation unit 41 counts
up the up / down counter, and proceeds to step S7. In step S5, the signal generation unit 41
counts down the up / down counter, and the process proceeds to step S7. Furthermore, in step
S6, the signal generation unit 41 holds the value of the up / down counter, and the process
proceeds to step S7. Finally, in step S7, the signal generation unit 41 generates and outputs a
control signal according to the value of the up / down counter. As described above, the stereo
microphone device 10 includes the level adjustment unit 30 so that the characteristics of the first
microphone 11, the first amplifier 13, and the first A / D converter 15, and When the same voice
is input to the first microphone 11 and the second microphone 12 regardless of the difference
between the characteristics of the second microphone 12, the second amplifier 14, and the third
A / D converter 16 The difference between the level of the signal output by the first A / D
converter 15 and the level of the signal output by the second A / D converter 16 can be
suppressed to, for example, about 0.3 dB. It becomes. Therefore, by providing the level
adjustment unit 30, the stereo microphone device 10 can improve the calculation accuracy of the
calculations 1, 2 and 3, and can reduce noise with high accuracy. Second Embodiment Next, a
second embodiment of the present invention will be described.
As shown in FIG. 9, the stereo microphone device 50 of the present embodiment includes the
noise reduction processing unit 51 in place of the noise reduction processing unit 17 in the
stereo microphone of the first embodiment. It has the same configuration as the device 10.
Therefore, in the present embodiment, only the noise reduction processing unit 51 will be
described, and the other parts will be assigned the same reference numerals and descriptions
thereof will be omitted. The noise reduction processing unit 51 extracts a signal of a touch noise
band from the signal output by the first A / D converter 15. A first noise band extraction unit 52
and a first noise band extraction unit 52: A first attenuator 53 for halving the signal output by
52, and a second noise band extraction for extracting a signal of a touch noise band from the
signal output by the second A / D converter 16 Unit 54, a second attenuator 55 which halves the
signal output by the second noise band extraction unit 54, a signal output by the first attenuator
53, and the second attenuator 55. A first adder 56 for adding the signal output by the first noise
filter 52 and a second adder for subtracting the signal output by the first adder 56 from the
signal output by the first noise band extraction unit 52 57 and the second noise And a third
adder 58 for subtracting the signal output by the first adder 56 from the signal output by the
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band extraction unit 54. Further, the noise reduction processing unit 51 is a first adaptive noise
reduction apparatus to which the signal output by the first A / D converter 15 and the signal
output by the second adder 57 are supplied. (Adaptive Noise Cancellar; hereinafter referred to as
ANC. And a second ANC 61 to which the signal output by the second A / D converter 16 and the
signal output by the third adder 58 are supplied. The signal output from the first ANC 60 and the
signal output by the second ANC 61 are supplied to the directional calculation processing unit
18. The microphone device 50 may not include the first noise band extraction unit 52 and the
second noise band extraction unit 54. When the first noise band extraction unit 52 and the
second noise band extraction unit 52 are not provided, noise generated in bands other than the
touch noise band can also be reduced. The noise reduction processing unit 51 performs the
calculation described below. First, the first attenuator 53 halves the signal Rs + Rn supplied by
the first A / D converter 15 to 1?2 (Rs + Rn).
The second attenuator 55 halves the signal Ls + Ln supplied by the second A / D converter 16 to
1?2 (Ls + Ln). Next, the first adder 56 performs an operation 11 shown below. 1/2 (Rs + Rn) +
1/2 (Ls + Ln) = 1/2 (Rs + Ls) + 1/2 (Rn + Ln) = 1/2 (Rs + Ls) = Rs = Ls Operation 11 Next, The
second adder 57 performs the operation 12 shown below. (Rs + Rn) -Rs = Rn. Operation 12 The
third adder 58 performs the operation 13 described below. (Ls + Ln) ?Ls = Ln Operation 13 In
the present embodiment, since the first noise band extraction unit 52 and the second noise band
extraction unit 54 are provided. The operations 11, 12, and 13 are performed only in the noise
band, but when the first noise band extracting unit 52 and the second noise band extracting unit
54 are not provided, the operations 11, 12, and 13 are performed. The operation 13 is
performed over the entire band of the audio signal. That is, the signal Rs + Rn and the vibration
noise Rn are supplied to the first ANC 60, and Ls + Ln and the vibration noise Ln are supplied to
the second ANC 61. The first ANC 60 performs a further operation on the signal Rs + Rn and the
vibration noise Rn to generate a noise-reduced signal for the right channel, and the second ANC
61 generates the signal Ls + Ln and the vibration noise Ln. Further operations are performed to
generate a noise-reduced signal for the left channel. The details of the calculation performed by
the first ANC 60 and the second ANC 61 will be described later. The first ANC 60 will be
described in detail below. The first ANC 60 adaptively controls the vibration noise Rn output
from the first delay unit 62 to which the signal is supplied from the first A / D converter 15 and
the second adder 57. First adaptive filter 63, and the signal output by the first delay filter 62 is
subtracted from the signal output by the first adaptive filter 63, and the result of subtraction is
the directional arithmetic processing unit 18 and the first And a fourth adder 64 for supplying to
the adaptive filter 63 of The first delay unit 62 controls the timing at which the signal output by
the first A / D converter 15 is supplied to the + terminal of the fourth adder 64.
More specifically, the first A / D converter 15 outputs a signal and supplies the signal to the first
delay unit 62 and the first noise band extraction unit 52. The first delay unit 62 receives the
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signal supplied to the first noise band extraction unit 52 as a first attenuator 53, a first adder 56,
a second adder 57, and a first adaptive filter 63. The supplied signal is held until it is supplied to
the-terminal of the fourth adder 64 via the. Then, the first delay unit 62 performs a fourth adder
64 on the signal held at the same timing as the signal is supplied from the first adaptive filter 63
to the negative terminal of the fourth adder 64. Supply to the + terminal of The first adaptive
filter 63 is also referred to as vibration noise Rn (hereinafter, referred to as a reference signal
X0) output by the second adder 57. And the signal output by the fourth adder 64 (hereinafter
also referred to as residual signal E). And adaptive filter processing is performed on the vibration
noise Rn to generate and output a pseudo noise signal Y1 having high correlation to the vibration
noise Rn. The details of the first adaptive filter 63 will be described later. The fourth adder 64
subtracts the pseudo noise signal Y1 having high correlation with the vibration noise Rn from the
signal Rs + Rn supplied by the first delay unit 62, thereby generating the vibration noise Rn and
the acoustic noise. Generate a signal R ? from which noise and noise have been removed. The
first adaptive filter 63 will be described in detail below. As shown in FIG. 10, the first adaptive
filter 63 performs an operation on the input reference signal X0 to generate and output a pseudo
noise signal Y1, and the input reference signal An LMS circuit 72 is provided to calculate
coefficients used in the calculation of the FIR filter 71 from X0 and the residual signal E. The FIR
filter 71 delays the input signal and outputs m (where m is an integer of 2 or more). Coefficients
calculated by the LMS circuit 72 for each of the delay devices 73-1, 73-2, ... 73-m, the reference
signal X0, and the signals output from the respective delay devices 73-1 to 73-m. And m + 1
multipliers 74-0, 74-1,... 74-m, and the signals output by the respective multipliers 74-0 to 74-m
are added to be correlated with the reference signal X0. And an adder 75 for generating and
outputting a high pseudo noise signal Y1. The delay units 73-2 to 73-m hold the signal output by
the delay unit provided one before, and delay the signal by a unit sampling time to output.
That is, the delay unit 73-h (where h is a natural number of 2 or more and m or less). ) Hold,
delay and output the signal output from the delay unit 73- (h-1). Also, the delay unit 73-1 holds
the reference signal X0, delays it by unit sampling time, and outputs it. Therefore, the reference
signal is X0, the signals output by the delay units 73-1 to 73-m are X1, X2, ... Xm, and the
coefficients of the multipliers 74-0 to 74-m are Assuming that W0, W1,... Wm, the pseudo noise
signal Y1 output from the adder 75 is calculated by a convolution operation as shown by the
following operation 21. The LMS circuit 72 calculates coefficients from the reference signal X0
and the residual signal E according to the LMS (Least Mean Square) algorithm. W0, W1, ... Wm
are calculated. Specifically, coefficients W0, W1,... Wm are calculated by performing the
following operation 22. <Img class = "EMIRef" id = "19818402-00004" /> where k is an integer. )
Indicates the sampling time has elapsed. That is, assuming that the coefficient Wk at the kth
sampling is the current coefficient, Wk-1 indicates the kth-1th sampling, that is, a coefficient in
the past at one sampling. Also, ? is a gain factor (step gain, step size) that determines the speed
and stability of adaptation. The LMS circuit 72 generates the pseudo noise signal Y1 highly
correlated with the reference signal X0 by performing the operation 21, and correlates with the
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vibration noise Rn included in the signal output by the fourth adder 64. Minimize high quality
signals. The algorithm used in the first adaptive filter 63 is not limited to the LMS algorithm.
However, since the convergence speed is relatively fast and the computation scale is small, the
LMS algorithm is often used. The calculation in the LMS circuit 72 can be processed by hardware
using a DSP (Digital Signal Processor) and digital LSI (Large Scale Integration) or software using a
microcomputer.
The second ANC 61 includes a second delay 81, a second adaptive filter 82, and a fifth adder 83.
The second delay 81 has a first delay. The second adaptive filter 82 corresponds to the first
adaptive filter 63, and the fifth adder 83 corresponds to the fourth adder 64. The second ANC 61
is the same as the first ANC 60 except that Ln and Ls + Ln are supplied instead of Rn and Rs + Rn,
and outputs the pseudo noise signal Y2 instead of the pseudo noise signal Y1. Therefore, the
detailed description of the second ANC 61 is omitted. The operation of the stereo microphone
device 50 will be described below. The operation until the A / D conversion of the signals
supplied by the first and second A / D converters 15 and 16 is the same as that of the stereo
microphone device 10, so the description will be omitted. The first A / D converter 15 supplies
the A / D converted signal to the first noise band extraction unit 52 and the first delay unit 62.
The second A / D converter 16 supplies the A / D converted signal to the second noise band
extraction unit 54 and the second delay unit 81. Next, the first noise band extraction unit 52
extracts the signal of the touch noise band from the signal supplied by the first A / D converter
15 and supplies the signal to the first attenuator 53. Further, the second noise band extraction
unit 54 extracts a signal of the touch noise band from the signal supplied by the second A / D
converter 16 and supplies the signal to the second attenuator 55. Next, the first attenuator 53
halves the signal supplied by the first noise band extraction unit 52 to generate 1?2 (Rs + Rn),
and the first adder 56 Supply to Further, the second attenuator 55 halves the signal supplied by
the second noise band extraction unit 54 to generate 1?2 (Ls + Ln) and supplies it to the first
adder 56. Next, the first adder 56 performs operation 11 to generate the audio signal Rs (= Ls),
and the ? terminal of the second adder 57 and the ? terminal of the third adder 58 Supply to
Next, the second adder 57 performs operation 12 to generate the vibration noise Rn, and
supplies the vibration noise Rn to the first adaptive filter 63. In addition, the third adder 58
performs the operation 13 to generate the vibration noise Ln, and supplies the vibration noise Ln
to the second adaptive filter 82. Next, the first adaptive filter 63 generates a pseudo noise signal
Y 1 from the supplied vibration noise Rn and supplies the pseudo noise signal Y 1 to the ?
terminal of the fourth adder 64.
Further, the second adaptive filter 82 generates a pseudo noise signal Y2 from the supplied
vibration noise Ln and supplies the pseudo noise signal Y2 to the-terminal of the fifth adder 83.
Next, the fourth adder 64 subtracts the pseudo noise signal Y1 from the signal supplied by the
first delay unit 62 to generate vibration noise from the signal Rs + Rn output by the first
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microphone 11. A signal having a high correlation with Rn is subtracted, that is, a signal R ?
from which the vibration noise Rn and the acoustic noise are removed. The signal R ? is
supplied to the directional calculation processing unit 18 and the first adaptive filter 63. In
addition, the fifth adder 83 subtracts the pseudo noise signal Y2 from the signal supplied by the
second delay unit 81, thereby correlating the signal Ls + Ln output from the second microphone
12 with the vibration noise Ln. Generates a signal L ? from which the high signal is subtracted,
that is, the vibration noise Ln and the acoustic noise are removed. The signal L ? is supplied to
the directional calculation processing unit 18 and the second adaptive filter 82. Finally, the
directional calculation processing unit 18 performs an operation on R ? to generate and output
an audio signal for the right channel, and performs an operation on L ? to perform an operation
on the left channel. Generate and output an audio signal of As described above, the noise
reduction processing unit 51 provided in the stereo microphone device 50 to which the present
invention is applied generates the vibration noise Rn and the vibration noise Ln by performing
the calculations 11, 12, and 13. . Then, an adaptive filter process is performed on Rn to generate
a pseudo noise signal Y1 correlated with Rn, which is subtracted from the signal Rs + Rn to
output an audio signal R ? in which the vibration noise Rn and the acoustic noise are reduced.
Further, by applying an adaptive filter process to Ln, a pseudo noise signal Y2 correlated with Ln
is generated and subtracted from the signal Ls + Ln to output an audio signal L ? with reduced
vibration noise Ln and acoustic noise. Therefore, the stereo microphone device 50 to which the
present invention is applied outputs two-channel audio with reduced vibration noises Rn and Ln
and acoustic noise even though two microphones are provided. It is possible to Further, in the
stereo microphone device 50 to which the present invention is applied, the first adaptive filter 63
generates a pseudo noise signal Y1 similar to the noise included in the signal Rs + Rn output by
the first microphone 11, The second adaptive filter 82 generates a pseudo noise signal Y2 similar
to the noise contained in the signal Ls + Ln output by the second microphone 12.
That is, since the stereo microphone device 50 to which the present invention is applied
processes the signal Rs + Rn and the signal Ls + Ln respectively with independent adaptive filters,
for example, noise included in the signal Rs + Rn and noise included in the signal Ls + Ln Even
when there is a phase difference or level difference between the two, noise can be reduced with
high accuracy. It is preferable that the stereo microphone device 50 also have the level
adjustment unit 30 between the first A / D converter 15 and the second A / D converter 16 and
the noise reduction processing unit 17. . The stereo microphone device 50 includes the level
adjustment unit 30 so that the level of the signal output by the first A / D converter 15 and the
level of the signal output by the second A / D converter 16 can be obtained. Since it becomes
possible to suppress the difference between the two, it becomes possible to improve the
calculation accuracy of the calculations 11, 12, and 13, and it becomes possible to reduce noise
with high accuracy. In the first embodiment, only the vibration noises Ln and Rn are reduced, but
in the second embodiment, they are included in the signals Ls and Rs in addition to the vibration
noises Ln and Rs. It is characterized in that acoustic noise correlated with Rn is simultaneously
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reduced. Third Embodiment Next, the third embodiment of the present invention will be
described in detail. As shown in FIG. 11, the stereo microphone device 100 of the present
embodiment includes the noise reduction processing unit 101 in place of the noise reduction
processing unit 51, except for the stereo microphone device 10 of the first embodiment. It has
the same configuration as Therefore, in the stereo microphone device 100 according to the
present embodiment, only the noise reduction processing unit 101 will be described, and the
other parts will be assigned the same reference numerals and descriptions thereof will be
omitted. The same parts as those of the stereo microphone device 50 of the second embodiment
are also assigned the same reference numerals and explanation thereof is omitted. The noise
reduction processing unit 101 outputs a third attenuator 102 that halves the signal output by the
first noise band extraction unit 52 and a second noise band extraction unit 54. A fourth
attenuator 103 that halves the signal, and a sixth adder 104 that subtracts the signal output by
the third attenuator 102 from the signal output by the fourth attenuator 103; A third delay 105
to which a signal is supplied from the first A / D converter 15, a signal output by the sixth adder
104 and a signal output by the third delay 105 are added. The seventh adder 106, the fourth
delay unit 107 to which a signal is supplied from the second A / D converter 16, and the signal
output by the fourth delay unit 107 are processed by the sixth adder 104. Second to subtract the
output signal And eight adders 108.
The third delay unit 105 controls the timing at which the signal output by the first A / D
converter 15 is supplied to the seventh adder 106. Specifically, first, the first A / D converter 15
outputs a signal and supplies the signal to the third delay unit 105 and the first noise band
extraction unit 52. Next, the third delay unit 105 supplies the signal supplied to the first noise
band extraction unit 52 to the seventh adder 106 via the third attenuator 102 and the sixth
adder 104. Hold the supplied signal until it is Then, the third delay unit 105 supplies the held
signal to the seventh adder 106 at the same timing as the signal is supplied from the sixth adder
104 to the seventh adder 106. . The fourth delay unit 107 controls the timing at which the signal
output by the second A / D converter 16 is supplied to the + terminal of the eighth adder 108.
Specifically, first, the second A / D converter 16 outputs a signal and supplies the signal to the
fourth delay unit 107 and the second noise band extraction unit 54. Next, the fourth delay unit
107 receives the signal supplied to the second noise band extraction unit 54 via the fourth
attenuator 103 and the sixth adder 104- Hold the supplied signal until it is supplied to the
terminal. Then, the fourth delay unit 107 receives the held signal at the + terminal of the eighth
adder 108 at the same timing as the timing at which the signal is supplied from the sixth adder
104 to the eighth adder 108. Supply to In the noise reduction processing unit 101, the third and
fourth attenuators 102 and 103 and the sixth adder 104 perform the operation 1, and the
seventh adder 106 performs the operation 2, and the eighth The adder 108 performs operation
3 to generate the signals Rs and Ls from which the vibration noises Rn and Ln have been
removed, and supply the signal Rs to the first delay device 62 provided in the first ANC 60, The
signal Ls is supplied to a second delay 81 provided in a second ANC 61. Hereinafter, the
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operation of the stereo microphone device 100 will be described. The operation until the A / D
conversion of the signals supplied by the first and second A / D converters 15 and 16 is the same
as that of the stereo microphone device 10, so the description will be omitted. The first A / D
converter 15 supplies the A / D converted signal to the first noise band extraction unit 52 and
the third delay unit 105. Also, the second A / D converter 16 supplies the A / D converted signal
to the second noise band extraction unit 54 and the fourth delay unit 107.
Next, the first noise band extraction unit 52 extracts the signal of the touch noise band from the
signal supplied by the first A / D converter 15, and the first attenuator 53, the second The plus
terminal of the adder 57 and the third attenuator 102 are supplied. Further, the second noise
band extraction unit 54 extracts the signal of the touch noise band from the signal supplied by
the second A / D converter 16, and the second attenuator 55 and the third adder 58 are
provided. The + terminal and the fourth attenuator 103 are supplied. Next, the first attenuator 53
halves the signal supplied by the first noise band extraction unit 52 to generate 1?2 (Rs + Rn),
and the first adder 56 Supply to Further, the second attenuator 55 halves the signal supplied by
the second noise band extraction unit 54 to generate 1?2 (Ls + Ln) and supplies it to the first
adder 56. Next, the first adder 56 performs operation 11 to generate Rs (= Ls), and supplies Rs (=
Ls) to the ? terminal of the second adder 57 and the ? terminal of the third adder 58. Do. Next,
the second adder 57 performs operation 12 to generate the vibration noise Rn, and supplies the
vibration noise Rn to the first adaptive filter 63. In addition, the third adder 58 performs the
operation 13 to generate the vibration noise Ln, and supplies the vibration noise Ln to the
second adaptive filter 82. Next, the first adaptive filter 63 generates the pseudo noise signal Y1
? from the supplied vibration noise Rn, and supplies the pseudo noise signal Y1 ? to the ?
terminal of the fourth adder 64. Further, the second adaptive filter 82 generates a pseudo noise
signal Y2 'from the supplied vibration noise Ln, and supplies the pseudo noise signal Y2' to theterminal of the fifth adder 83. On the other hand, the third attenuator 102 halves the signal
supplied by the first noise band extraction unit 52 to generate 1?2 (Rs + Rn). -Supply to the
terminal. Further, the fourth attenuator 103 multiplies the signal supplied by the second noise
band extraction unit 54 by half to generate 1?2 (Ls + Ln), and generates the signal at the +
terminal of the sixth adder 104. Supply. Next, the sixth adder 104 performs operation 1 to
generate 1?2 (L n ?R n), and generates the seventh adder 106 and the ? terminal of the eighth
adder 108. Supply. Further, the third delay unit 105 is the same as the timing at which the sixth
adder 104 supplies the signal to the seventh adder 106 with the signal supplied by the first A / D
converter 15. The timing is supplied to the seventh adder 106.
Also, the fourth delay unit 107 is the same as the timing at which the sixth adder 104 supplies a
signal to the ? terminal of the eighth adder 108 with the signal supplied by the second A / D
converter 16. At timing, the + terminal of the eighth adder 108 is supplied. Next, the seventh
adder 106 performs operation 2 to generate a noise-removed audio signal Rs, and supplies the
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audio signal Rs to the first delay unit 62. That is, the signal Rs is supplied to the first ANC circuit
60. The eighth adder 108 performs operation 3 to generate an audio signal Ls from which noise
has been removed, and supplies the audio signal Ls to the second delay unit 81. That is, the
signal Ls is supplied to the second ANC circuit 61. Next, the first delay 62 holds the signal Rs,
and at the same timing as the first adaptive filter 63 supplies the pseudo noise signal Y1 ? to
the ? terminal of the fourth adder 64, The held signal Rs is supplied to the + terminal of the
fourth adder 64. Also, the second delay 81 holds the signal Ls, and holds it at the same timing as
the second adaptive filter 82 supplies the pseudo noise signal Y2 ? to the ? terminal of the fifth
adder 83. The signal Ls is supplied to the + terminal of the fifth adder 83. Next, the fourth adder
64 subtracts the pseudo noise signal Y1 ? from the signal Rs supplied by the first delay unit 62
to have high correlation with the vibration noise Rn from the sound signal Rs. A signal R ? is
generated by subtracting the signal from the signal Rs. The signal R ? ? is supplied to the
directional calculation processing unit 18 and the first adaptive filter 63. Further, the fifth adder
83 subtracts the pseudo noise signal Y2 ? from the signal Ls supplied by the second delay unit
81, thereby subtracting a signal highly correlated with the vibration noise Ln from the signal Ls.
That is, it generates a signal L ? ? from which the acoustic noise is removed from the signal Ls.
The signal L ? ? is supplied to the directional calculation processing unit 18 and the second
adaptive filter 82. Finally, the directional calculation processing unit 18 performs an operation
on the signal R ? ? to generate and output an audio signal for the right channel, and performs
an operation on the signal L ? ? to execute the left operation. Generate and output an audio
signal for a channel. As described above, the noise reduction processing unit 101 provided in the
stereo microphone device 100 to which the present invention is applied includes the third
attenuator 102, the fourth attenuator 103, and the sixth adder 104; The seventh adder 106 and
the eighth adder 108 perform operations 1, 2 and 3 to generate the signals Rs and Ls from which
the vibration noise Rn and Ln have been removed.
The first attenuator 53, the second attenuator 55, the first adder 56, the second adder 57, and
the third adder 58 perform operations 11, 12 and 13 to generate vibration noise Rn, Generate
Ln. Then, the first ANC 60 generates and outputs the signal R ? ? from which the acoustic
noise is reduced from the signal Rs based on Rs and Rn, and the second ANC 61 reduces the
acoustic noise from the signal Ls based on Ls and Ln Generate and output the output signal L ?
?. Accordingly, in the stereo microphone device 100 to which the present invention is applied,
the first adaptive filter 63 and the second adaptive filter 82 can perform adaptive control
processing to reduce only acoustic noise. , Easy to converge. That is, the stereo microphone
device 100 to which the present invention is applied has a high noise reduction effect. It is
preferable that the stereo microphone device 100 also have the level adjustment unit 30 between
the first A / D converter 15 and the second A / D converter 16 and the noise reduction
processing unit 101. . The stereo microphone device 100 includes the level adjustment unit 30
so that the level of the signal output by the first A / D converter 15 and the level of the signal
output by the second A / D converter 16 can be obtained. It becomes possible to suppress the
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difference between the two, so that it is possible to generate 1?2 (Ls?Rn) with high accuracy and
to remove the vibration noises Rn and Ln with high accuracy, and to reduce the noise with high
accuracy. It becomes possible. According to the noise reduction apparatus and reduction method
of the present invention, first, the signal output by the first nondirectional microphone is
subtracted from the signal output by the second nondirectional microphone. A difference signal
is generated which is 1/2 the level of the signal. Next, the signal output by the first
nondirectional microphone and the difference signal are added and output, and the difference
signal is subtracted from the signal output by the second nondirectional microphone and output.
Further, in the noise reduction device and reduction method according to the present invention,
first, of the signal obtained by adding the signal output by the first nondirectional microphone
and the signal output by the second nondirectional microphone, A sum signal which is 1/2 level
is generated. Next, a signal obtained by subtracting the sum signal from the signal output by the
first microphone is adaptively controlled to generate a first pseudo noise signal.
Then, the first pseudo noise signal is subtracted from the signal output by the first nondirectional
microphone and output. Further, a signal obtained by subtracting the sum signal from the signal
output by the second microphone is adaptively controlled to generate a second pseudo noise
signal. Then, the second pseudo noise is subtracted from the signal output by the second
nondirectional microphone and output. Therefore, according to the noise reduction device and
the noise reduction method of the present invention, although the number of microphones
provided is two, the noise for the right channel voice and the left channel can be reduced. It is
possible to output voice and sound. Therefore, according to the noise reduction device and the
noise reduction method according to the present invention, it is possible to reduce the noise
output simultaneously with the voice for the right channel and the noise output simultaneously
with the voice for the left channel. It becomes easy to miniaturize. Further, according to the noise
reduction apparatus and the noise reduction method according to the present invention, it is
possible to sufficiently reduce the noise output simultaneously with the voice at low cost without
increasing the circuit scale. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of
a stereo microphone device according to a first embodiment of this invention. FIG. 2 is a diagram
showing the vibration of the diaphragm provided to the first microphone and the vibration of the
diaphragm provided to the second microphone, wherein (A) shows the time when an audio is
input , (B) shows the time when vibration noise is input. FIG. 3 is a diagram for explaining the
relationship between the microphone interval and the phase difference and level difference
between the signal R and the signal L; FIG. 4 is a schematic view showing another arrangement of
a first microphone and a second microphone. FIG. 5 is a block diagram of a stereo microphone
device provided with a level adjustment unit. FIG. 6 is a block diagram of a level difference
detection unit. 7A and 7B are diagrams showing signals in the level difference detection unit, in
which FIG. 7A shows the signal output by the LPF, and FIG. It shows the output signal. FIG. 8 is a
flowchart showing an operation of a level difference detection unit. FIG. 9 is a block diagram of a
stereo microphone device according to a second embodiment of the present invention. FIG. 10 is
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a block diagram showing a first adaptive filter provided in the stereo microphone device. FIG. 11
is a block diagram of a stereo microphone device according to a third embodiment of the present
invention.
FIG. 12 is a block diagram of a conventional stereo microphone device. Explanation of the code
10 stereo microphone device, 11 first microphone, 12 second microphone, 13 first amplifier, 14
second amplifier, 15 first A / D converter, 16 second A / D D converter, 17 noise reduction
processing unit, 18 directional arithmetic processing unit, 21 first attenuator, 22 second
attenuator, 23 first adder, 24 second adder, 25 first Delay, 26 second delay, 27 second adder, 28
third adder
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is in a predetermined direction, and the sound receiving surface is the first
nondirectional property. A second nondirectional microphone arranged in a direction different by
180 ░ with respect to the direction of the receiving surface of the microphone and at a
predetermined distance from the receiving surface of the first nondirectional microphone. And a
sum signal for generating a sum signal that is 1/2 times the level of the signal obtained by
adding the signal output by the first nondirectional microphone and the signal output by the
second nondirectional microphone Generation means, first operation means for subtracting the
sum signal from the signal output by the first nondirectional microphone, and the signal output
by the second nondirectional microphone A second operation means for subtracting the sum
signal; a first adaptive control means for adaptively controlling the signal output by the first
operation means to generate a first pseudo noise signal; A second adaptive control means for
adaptively controlling a signal output by the second arithmetic means to generate a second
pseudo noise signal; and a signal output from the first nondirectional microphone from the first
adaptive control means. , And fourth operation means for subtracting the second adaptive control
signal from the signal output by the second non-directional microphone; The adaptive control
means adaptively controls the signal output by the first arithmetic means based on the output
from the third arithmetic means, and the second adaptive control means controls the fourth
arithmetic means. Based on the output from the means Characterized in that it adaptively
controls signal output by said second calculating means.
In the noise reduction method according to the present invention, a first nondirectional
microphone arranged so that the sound receiving surface is in a predetermined direction, and a
sound receiving surface of the first nondirectional microphone A second nondirectional
microphone arranged in a direction different by 180 ░ with respect to the direction of the sound
receiving surface, and arranged at a predetermined distance from the sound receiving surface of
the first nondirectional microphone; It is a noise reduction method in a stereo microphone device
provided, wherein the level of a signal obtained by subtracting the signal output by the first
nondirectional microphone from the signal output by the second nondirectional microphone is
half the level of the signal A difference signal generating step of generating a difference signal
which is the first signal processing step of generating a difference signal, and a first operation
step of adding the signal output by the first nondirectional And flop, characterized in that it
comprises a second arithmetic step of subtracting the difference signal from the signal output by
the second omni-directional microphones. Further, in the noise reduction method according to
the present invention, the first nondirectional microphone is disposed such that the sound
receiving surface is in a predetermined direction, and the sound receiving surface includes the
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first nondirectional property. A second nondirectional microphone arranged in a direction
different by 180 ░ with respect to the direction of the receiving surface of the microphone and
at a predetermined distance from the receiving surface of the first nondirectional microphone. A
method of reducing noise in a stereo microphone device comprising: a sum signal obtained by
adding a signal output by the first nondirectional microphone and a signal output by the second
nondirectional microphone; A sum signal generation step of generating by doubling and a first
operation step of subtracting the sum signal from the signal output by the first nondirectional
microphone and outputting the result. And a second operation step of subtracting the sum signal
from the signal output by the second nondirectional microphone and outputting the signal
output in the first operation step. A first adaptive control step of generating a first pseudo noise
signal; and a second adaptive control step of generating a second pseudo noise signal that
adaptively controls the signal output in the second calculation step. A third operation step of
subtracting the first pseudo noise signal from the signal output by the first nondirectional
microphone, and the second operation signal from the signal output by the second nondirectional
microphone And a fourth operation step of subtracting the pseudo noise signal, and in the first
adaptive control step, the first operation is performed based on the signal output in the third
operation step. The signal output in the step is adaptively controlled, and in the second adaptive
control step, the signal output in the second calculation step is adaptively controlled based on the
output from the fourth calculation means It is characterized by
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present
invention will be described in detail with reference to the drawings. First Embodiment First, a
first embodiment of the present invention will be described. As shown in FIG. 1, a stereo
microphone device 10 to which the present invention is applied includes a first microphone
(hereinafter referred to as a microphone) 11 and a second microphone 12 for converting sound
into an electrical signal and outputting it. A first amplifier 13 for amplifying a signal output by
the first microphone 11, a second amplifier 14 for amplifying a signal output by the second
microphone 12, and a signal output by the first amplifier 13 Is analog-to-digital conversion
(hereinafter referred to as A / D conversion). ), A second A / D converter 16 for A / D converting
the signal output by the second amplifier 14, a first A / D converter 15, and A noise reduction
processing unit 17 that reduces noise contained in the signal output by the second A / D
converter 16 and a calculation performed on the signal output by the noise reduction processing
unit 17 A directional calculation processing unit 18 for generating an audio signal and an audio
signal for the left channel is provided. The stereo microphone device 10 is mounted on an
electronic device such as a video camera, for example, and collects audio to be recorded on a
recording medium such as a video tape or a disc-shaped recording medium. The first microphone
11 and the second microphone 12 are nondirectional microphones. The first microphone 11 and
the second microphone 12 convert the inputted sound waves into electrical signals. As shown in
FIGS. 2A and 2C, the first microphone 11 and the second microphone 12 are provided coaxially
so that the sound receiving surfaces face each other. The first microphone 11 includes a +
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terminal 11a and a-terminal 11b, the + terminal 11a is connected to the first amplifier 13, and
the-terminal 11b is grounded. Further, the second microphone 12 includes a + terminal 12 a and
a ? terminal 12 b, the + terminal 12 a is connected to the second amplifier 14, and the ?
terminal 12 b is grounded. When the first microphone 11 and the second microphone 12 are
provided such that their respective sound receiving surfaces face each other, the diaphragms 11
c and 12 c are shown in FIG. As shown in A), the voice signals Rs and Ls that are in phase and
vibrate in opposite directions with substantially the same phase are output.
Specifically, assuming that the first microphone 11 outputs the signal indicated by the solid line
in the left diagram of FIG. 2B when the diaphragms 11 c and 12 c vibrate as indicated by the
solid line, the second The microphone 12 outputs a signal shown by a solid line in the right
figure of FIG. 2 (B). Also, when the diaphragms 11c and 12c vibrate as shown by the broken line,
the first microphone 11 outputs a signal shown by the broken line in the left figure of FIG. 2B,
and the second microphone 12 B) Output a signal shown by a broken line in the right figure. On
the other hand, when an object comes in contact with the electronic device on which the stereo
microphone device 10 is mounted, touch noise including acoustic noise and vibration noise is
generated. When an object contacts the electronic device, for example, when vibration is
generated in the direction indicated by the arrow A, the diaphragms 11c and 12c vibrate in the
same direction as indicated by a solid line or a broken line in FIG. The first microphone 11 and
the second microphone 12 output vibration noises Rn and Ln which are in opposite phase to
each other. Specifically, assuming that the first microphone 11 outputs the signal indicated by
the solid line in the left diagram of FIG. 2D when the diaphragms 11 c and 12 c vibrate as
indicated by the solid line, the second The microphone 12 outputs a signal indicated by a solid
line in the right of FIG. 2D. Also, when the diaphragms 11c and 12c vibrate as shown by the
broken line, the first microphone 11 outputs a signal shown by the broken line in the left figure
of FIG. 2D, and the second microphone 12 D) Output a signal indicated by a broken line in the
right figure. When the vibration occurs in the direction indicated by the arrow B orthogonal to
the arrow A, the diaphragms 11 c and 12 c do not vibrate, and the first microphone 11 and the
second microphone 12 do not output a signal. . Here, an interval between the first microphone
11 and the second microphone 12 (hereinafter, referred to as a microphone interval. The
relationship between the phase difference and the level difference between the signal d) and the
signal R (= Rs + Rn) output by the first microphone 11 and the signal L (= Ls + Ln) output by the
second microphone 12 will be described. Do. First, the relationship between the microphone
interval d and the phase difference between the signal R and the signal L will be described. When
a sound wave of amplitude a outputted by the sound source A is input to the first microphone 11
and the second microphone 12, the distance between the sound source A and the first
microphone 11 or the second microphone 12 is a microphone If it is sufficiently larger than the
interval d, it is considered that the sound waves output by the sound source A are input
substantially parallel to the first microphone 11 and the second microphone 12 as shown in FIG.
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Further, if the microphone distance d is sufficiently smaller than the wavelength ? of the sound
wave output by the sound source A, Expression 1 and Expression 2 shown below hold. Signal R =
a и cos (?t) Equation 1 Signal L = a и cos (?t??) Equation 2 where ? represents an angular
velocity at which the sound travels through the air, ? indicates the distance between the second
microphone 12 and the point c where the straight line connecting the second microphone 12 and
the sound source A intersects with the perpendicular drawn from the first microphone 11 at the
straight line. That is, the phase difference between the sound input to the first microphone 11
and the sound input to the second microphone 12 is ?. Therefore, compared with the signal R
output by the first microphone 11, the signal L output by the second microphone 12 is a signal
shifted by a phase difference ? based on the delay due to the microphone interval d. Become.
Next, the relationship between the microphone interval d and the level difference between the
signal R and the signal L will be described. Speech is known to propagate in the air as
compression waves, but the maximum positive value (or the minimum negative value) of speech
is dense, and the minimum (or the maximum positive value) of speech is sparse. Then, when d>
? / 2, the sound wave reaching the second microphone 12 is output by the second microphone
12 in order to reach a level falling by becoming a shadow of the first microphone 11. The
amplitude of the signal is smaller than the amplitude of the sound output by the first microphone
11. However, when d ? ? / 2, the sound input to the second microphone 12 is output by the
first microphone 11 because it is hardly affected by the sound input to the first microphone 11.
And the amplitude of the signal output by the second microphone 12 are substantially the same.
As an example, when the microphone distance d is 15 mm, the frequency F with a half cycle of
15 mm is as shown in the following Equation 3 at normal temperature. Frequency F ? sonic
speed in air / 2 d = 340/2 и 15 = 11 kHz Equation 3 Therefore, assuming that the microphone
distance d is 15 mm, the first microphone 11 and the second microphone 12 The amplitude of
the signal R output by the first microphone 11 and the amplitude of the signal L output by the
second microphone 12 become substantially the same if the frequency of the sound wave
reaching the The difference with the signal L is only the phase difference ?. If the microphone
interval d is small, the influence of the phase difference ? can be ignored.
The first microphone 11 and the second microphone 12 always have an amplitude by
determining the microphone interval d such that the band of the touch noise is equal to or lower
than the frequency F or by limiting the band of the touch noise. Outputs a signal equal to. The
noise reduction processing unit 17 outputs a signal from the first A / D converter 15 by a first
attenuator 21 that halves the signal output from the first A / D converter 15 and a second A / D
converter 16. The second attenuator 22 that halves the received signal and a first adder 23 that
subtracts the signal output by the first attenuator 21 from the signal output by the second
attenuator 22. A noise band extraction unit 24 for extracting a signal of a predetermined band
from the signal output by the first adder 23, and a first delay unit 25 to which a signal is
supplied from the first A / D converter 15. , The second delay unit 26 to which the signal is
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supplied from the second A / D converter 16, the signal output by the noise band extraction unit
24 and the signal output by the first delay unit 25 are added. And the second adder 27 that
supplies the directional calculation processing unit 18 And a third adder 28 for subtracting the
signal output from the noise band extraction unit 24 from the signal output from the first delay
unit 25 and supplying the result to the directional calculation processing unit 18. The noise band
extraction unit 24 is configured of a low pass filter (LPF), a band pass filter (BPF), and the like.
The touch noise occurs concentrated on the relatively low frequency of the signals output by the
first microphone 11 and the second microphone 12 (hereinafter, a band in which touch noise
occurs is referred to as a touch noise band). The noise band extraction unit 24 extracts and
outputs a signal of the touch noise band from the audio signal. By including the noise band
extraction unit 24, the stereo microphone device 10 can efficiently reduce touch noise. The
microphone device 10 may not include the noise band extraction unit 24. When the noise band
extraction unit 24 is not provided, the noise reduction processing unit 17 can also reduce noise
generated in a band other than the touch noise band. The first delay unit 25 controls the timing
at which the signal output by the first A / D converter 15 is supplied to the second adder 27.
Specifically, first, the first A / D converter 15 outputs a signal and supplies it to the first delay 25
and the first attenuator 21.
Next, the first delay unit 25 continues until the signal supplied to the first attenuator 21 is
supplied to the second adder 27 via the first adder 23 and the noise band extraction unit 24.
Hold the supplied signal. Then, the first delay unit 25 supplies the held signal to the second
adder 27 at the same timing as the signal is supplied from the noise band extraction unit 24 to
the second adder 27. The second delay unit 26 controls the timing at which the signal output by
the second A / D converter 16 is supplied to the + terminal of the third adder 28. More
specifically, the second A / D converter 16 outputs a signal to the second delay unit 26 and the
second attenuator 22. Next, in the second delay unit 26, the signal supplied to the second
attenuator 22 is supplied to the-terminal of the third adder 28 via the first adder 23 and the
noise band extraction unit 24. Hold the supplied signal until Then, the second delay unit 26 is
configured to hold the signal held by the third adder 28 at the same timing as the signal is
supplied from the noise band extraction unit 24 to the negative terminal of the third adder 28.
Supply to + terminal. The noise reduction processing unit 17 performs the operation described
below. First, the first attenuator 21 halves Rs + Rn output from the first A / D converter 15 to 1?2
(Rs + Rn). The second attenuator 22 halves Ls + Ln output from the second A / D converter 16 to
1?2 (Ls + Ln). Next, the first adder 23 performs an operation 1 shown below. Since Ls and Rs
have substantially the same amplitude and the same phase, Ls-Rs can be set to 0. 1/2 (Ls + Ln)1/2 (Rs + Rn) = 1/2 (Ls-Rs) + 1/2 (Ln-Rn) = 1/2 (Ln-Rn) иии Operation 1 Next, the second adder 27
performs the following operation 2. Since Ln and Rn have substantially the same amplitude and
opposite phase, Ln + Rn = 0. (Rs + Rn) + 1/2 (Ln-Rn) = Rs + 1/2 Ln + Rn-1/2 Rn = Rs + 1/2 (Ln +
Rn) = Rs Operation 2 The third adder 28 Perform operation 3 shown in. (Ls + Ln)-1/2 (Ln-Rn) =
Ls + Ln-1/2 Ln + 1/2 Rn = Ls + 1/2 (Ln + Rn) = Ls Operation 3 In the present embodiment, the
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noise band Since the extracting unit 24 is provided, the operations 2 and 3 are performed only in
the noise band, but when the noise band extracting unit 24 is not provided, the operations 2 and
3 are all bands of the audio signal. It takes place over
Next, the operation of the stereo microphone device 10 will be described. First, when voice is
input, the first microphone 11 and the second microphone 12 convert the input voice into an
electrical signal and output it. The output Rs + Rn of the first microphone 11 is supplied to the
first amplifier 13, and the output Ls + Ln of the second microphone 12 is supplied to the second
amplifier 14. Next, the first amplifier 13 amplifies the signal supplied by the first microphone 11
and supplies the amplified signal to the first A / D converter 15. Also, the second amplifier 14
amplifies the signal supplied by the second microphone 12 and supplies the amplified signal to
the second A / D converter 16. Next, the first A / D converter 15 A / D converts the signal
supplied by the first amplifier 13 and supplies it to the first attenuator 21 and the first delay
device 25. . Further, the second A / D converter 16 A / D converts the signal supplied by the
second amplifier 14 and supplies the signal to the second attenuator 22 and the second delay 26.
Next, the first attenuator 21 halves the signal supplied by the first A / D converter 15 to generate
1?2 (Rs + Rn), and the first adder Supply to the 23-terminal. In addition, the second attenuator 22
halves the signal supplied by the second A / D converter 16 to generate 1?2 (Ls + Ln), and the
positive terminal of the first adder 23 Supply to Next, the first adder 23 performs operation 1 to
generate 1?2 (L n ?R n), which is supplied to the noise band extraction unit 24. Next, the noise
band extraction unit 24 extracts a signal of the touch noise band from the signal supplied by the
first adder 23, and the second adder 27 and the third adder 28 Supply to the terminal. On the
other hand, the first delay unit 25 has the same timing as the timing at which the noise band
extraction unit 24 supplies the signal to the second adder 27 with the signal supplied by the first
A / D converter 15. , To the second adder 27. Also, the second delay unit 26 has the same timing
as the signal supplied by the second A / D converter 16 and the timing at which the noise band
extraction unit 24 supplies the signal to the-terminal of the third adder 28 To the + terminal of
the third adder 28. Next, the second adder 27 performs operation 2 to generate a signal Rs from
which the vibration noise Rn has been removed, and supplies the signal Rs to the directional
calculation processing unit 18.
The third adder 28 also performs operation 3 to generate the signal Ls from which the vibration
noise Ln is removed, and supplies the signal Ls to the directional calculation processing unit 18.
Finally, the directional calculation processing unit 18 performs an operation on the signal Rs to
generate and output an audio signal for the right channel, and performs an operation on the
signal Ls for the left channel. Generate and output an audio signal of As described above, in the
stereo microphone device 10 to which the present invention is applied, the first microphone 11
and the second microphone 12 are disposed such that the sound receiving surfaces thereof face
each other. Therefore, the audio signal Rs and the audio signal Ls have the same phase, and the
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vibration noise Rn and the vibration noise Ln have the opposite phase. That is, the audio signal
Rs and the audio signal Ls are substantially zero when subtracted, and the vibration noise Rn and
the vibration noise Ln are substantially zero. The noise reduction processing unit 17 provided in
the stereo microphone device 10 to which the present invention is applied can execute the
operations 1, 2 and 3 by the circuit configuration described above, and the audio signal Rs and
the audio signal The voice signal Rs from which the vibration noise Rn is removed and the voice
signal Ls from which the vibration noise Ln is removed are generated and output using the
relationship with Ls and the relationship between the vibration noise Rn and the vibration noise
Ln. . That is, the stereo microphone device 10 to which the present invention is applied outputs
the noise for the right channel voice and the noise for the left channel, although the number of
microphones provided is two. It is possible to Therefore, the stereo microphone device 10 to
which the present invention is applied can reduce the noise output simultaneously with the
sound for the right channel and the noise output simultaneously with the sound for the left
channel, and can be miniaturized. Is easy. Further, when the stereo microphone device 10 to
which the present invention is applied is mounted on an electronic device such as a video
camera, the mounted electronic device has noise simultaneously output with audio for the right
channel, audio for the left channel, It is possible to reduce noise that is output simultaneously,
and it becomes easy to miniaturize. Furthermore, the stereo microphone device 10 to which the
present invention is applied can sufficiently reduce noise without increasing the directional
arithmetic processing unit 18 or attaching a new A / D converter or the like. it can. Therefore, the
stereo microphone device 10 to which the present invention is applied can sufficiently reduce the
noise output simultaneously with the voice by the first microphone 11 and the second
microphone 12 at low cost without increasing the circuit size.
In the stereo microphone device 10 to which the present invention is applied, the noise reduction
processing unit 17 performs the operation 1 to output the signal Rs + Rn output from the first
microphone 11 and the second microphone 12. From the signal Ls + Ln, 1?2 (Ln?Rn) is
generated. 1/2 (Ln-Rn) is the same as the vibration noise Ln, is in reverse phase and has the
same level as the vibration noise Rn. The signal Ls is generated by subtracting 1?2 (Ln?Rn) from
the signal Ls + Ln, and the signal Rs is generated by adding the signals Rs + Rn and 1?2 (Ln?Rn).
That is, the stereo microphone device 10 to which the present invention is applied extracts
vibration noises Rn and Ln and subtracts them from the signals output by the first microphone
11 and the second microphone 12 without providing a vibration pickup microphone. The same
operation as the operation can be performed. Therefore, it is possible to avoid the problem that
the voice can not be reduced with high accuracy since the voice is input to the vibration pickup
microphone. Further, by providing the vibration pickup, it is possible to prevent difficulty in size
reduction and cost reduction. The first microphone 11 and the second microphone 12 may be
disposed so that the sound receiving surfaces face in directions different from each other by 180
░, for example, as shown in FIG. You may arrange so that a sound surface may face outside.
Further, the first microphone 11 and the second microphone 12 may not be arranged coaxially.
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By the way, the first microphone 11 and the second microphone 12 provided in the stereo
microphone device 10 have different levels of signals output when the same sound is input due
to variations in manufacturing, etc. It may not be identical. Further, the first amplifier 13 and the
second amplifier 14 have different levels of signals output when signals of the same level are
input due to variations in constants such as external resistors. There is. Furthermore, with
respect to the first A / D converter 15 and the second A / D converter 16, the levels of the signals
output when the same level signal is input may not be the same. That is, in the stereo
microphone device 10, the characteristics of the first microphone 11, the first amplifier 13, and
the first A / D converter 15, and the second microphone 12, the second amplifier 14, and the
second Of the first A / D converter 16 when the same voice is input to the first microphone 11
and the second microphone 12. The level of the signal output by 15 and the level of the signal
output by the second A / D converter 16 may differ.
Therefore, as shown in FIG. 5, in the stereo microphone device 10, the level adjustment between
the first A / D converter 15 and the second A / D converter 16 and the noise reduction
processing unit 17 is performed. Preferably, a portion 30 is provided. The level adjustment unit
30 will be described below. The level adjustment unit 30 receives the signal output from the
second A / D converter 16, the level change unit 31, the signal output from the level change unit
31, and the first A / D conversion. A level difference detection unit 32 is provided which
generates a level control signal based on the signal output by the unit 15 and supplies the
generated level control signal to the level change unit 31. The level change unit 31 amplifies or
attenuates the signal output by the second A / D converter 16 based on the level control signal
supplied by the level difference detection unit 32, and outputs the signal to reduce noise. The
signal is supplied to the unit 17 and the level difference detection unit 32. Based on the level
control signal supplied by the level difference detection unit 32, the level change unit 31 makes
the level of the signal output by itself the same as the level of the signal output by the first A / D
converter 15. The signal output by the second A / D converter 16 is amplified or attenuated and
output while changing the amplification factor or the attenuation factor. The level difference
detection unit 32 compares the level of the signal output by the first A / D converter 15 with the
level of the signal output by the level change unit 31, and based on the comparison result, the
level control is performed. A signal is generated and supplied to the level change unit 31.
Specifically, as shown in FIG. 6, the level difference detection unit 32 of the present embodiment
removes a high frequency signal from the signal output by the first A / D converter 15. A first
LPF 33, a first absolute value converting unit 34 for absoluteizing a signal output by the first LPF
33, and a first peak detecting unit for detecting a peak of the signal output by the first absolute
value converting unit 34 Peak detection unit 35, a second LPF 36 outputting a low band signal
among the signals supplied by the level change unit 31, and a second absolute value converting
the signal output by the second LPF 36 into an absolute value Second peak detection unit 38
from the signal output from the first peak detection unit 35 and the second peak detection unit
38 for detecting the peak of the signal output from the second conversion unit 37 and the
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second absolute value conversion unit 37 Exit by section 38 An adder 39 that subtracts the input
signal, a code detection unit 40 that detects the sign of the signal output by the adder 39 and
outputs a signal indicating the detection result, and a signal that is output by the code detection
unit 40 And a signal generation unit 41 that generates a level control signal based on the
The first LPF 33 and the second LPF 36 are inserted to extract a signal in a band sufficiently low
with respect to the frequency F depending on the microphone distance d shown in Equation 3.
Thus, the amplitude of the signal output by the first LPF 33 and the amplitude of the signal
output by the second LPF 36 are the same as those of the first microphone 11, the first amplifier
13, and the first A / D converter 15. And the characteristics of the second microphone 12, the
second amplifier 14, and the second A / D converter 16 except for the difference due to the
variation. The first and second peak detectors 35 and 38 detect peaks of the signals output by
the first and second absolute value converters 34 and 37. Here, peak detection will be described
in detail. First, the signal R output by the first LPF 33 has the waveform shown in the left
diagram of FIG. 7A, and the signal L output by the second LPF 36 has the waveform shown in the
left diagram of FIG. 7B. Then, the signal R output by the first absolute value conversion unit 34
has a waveform shown by the solid line in the right diagram of FIG. 7A, and the signal L output
by the second absolute value conversion unit 37 is as shown in FIG. ) The waveform shown by
the solid line in the right figure. Furthermore, the signal R output by the first peak detection unit
35 has a waveform shown by the broken line in the right diagram of FIG. 7A, and the signal L
output by the second peak detection unit 38 is FIG. 7B. It becomes the waveform shown by the
broken line in the right figure. When the processing described above is performed and the level
of the signal R is compared with the level of the signal L at time T, a delay Td depending on the
microphone distance d occurs between the signal R and the signal L. Also, it can be seen that
although there is a level difference after absolute value conversion, almost no level difference
occurs after peak detection. Therefore, the level difference after peak detection is determined by
the characteristics of the first microphone 11, the first amplifier 13, the first A / D converter 15,
the second microphone 12, the second amplifier 14, the second Most of them are attributable to
the difference from the characteristics of the A / D converter 16. The adder 39 subtracts the level
of the signal output by the second peak detection unit 38 from the level of the signal output by
the first peak detection unit 35. Therefore, the sign of the signal output from the adder 39 is
positive when the level of the signal output by the first A / D converter 15 is greater than the
level of the signal output by the second A / D converter 16 When the level of the signal output
by the first A / D converter 15 is smaller than the level of the signal output by the second A / D
converter 16, the first A / D converter 15 becomes negative. When the level of the signal output
by the second A / D converter 16 is the same, the level is 0.
The signal generation unit 41 is configured such that, based on the signal supplied by the code
detection unit 40, the level of the signal output by the level change unit 31 is the same as that of
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the signal output by the first A / D converter 15. A level control signal is supplied to the level
change unit 31 so as to be equal to the level. In the present embodiment, the signal generation
unit 41 is configured by an up / down counter. To describe the generation of the level control
signal by the signal generation unit 41 in detail, first, as shown in FIG. Next, in step S2, it is
determined whether the signal supplied from the code detection unit 40 is positive. If the sign is
not positive, the process proceeds to step S3. If the sign is positive, the process proceeds to step
S4. Next, in step S3, it is determined whether the signal supplied from the code detection unit 40
is negative. When the sign is negative, the process proceeds to step S5, and when the sign is not
negative, the process proceeds to step S6. Then, in step S4, the signal generation unit 41 counts
up the up / down counter, and proceeds to step S7. In step S5, the signal generation unit 41
counts down the up / down counter, and the process proceeds to step S7. Furthermore, in step
S6, the signal generation unit 41 holds the value of the up / down counter, and the process
proceeds to step S7. Finally, in step S7, the signal generation unit 41 generates and outputs a
control signal according to the value of the up / down counter. As described above, the stereo
microphone device 10 includes the level adjustment unit 30 so that the characteristics of the first
microphone 11, the first amplifier 13, and the first A / D converter 15, and When the same voice
is input to the first microphone 11 and the second microphone 12 regardless of the difference
between the characteristics of the second microphone 12, the second amplifier 14, and the third
A / D converter 16 The difference between the level of the signal output by the first A / D
converter 15 and the level of the signal output by the second A / D converter 16 can be
suppressed to, for example, about 0.3 dB. It becomes. Therefore, by providing the level
adjustment unit 30, the stereo microphone device 10 can improve the calculation accuracy of the
calculations 1, 2 and 3, and can reduce noise with high accuracy. Second Embodiment Next, a
second embodiment of the present invention will be described.
As shown in FIG. 9, the stereo microphone device 50 of the present embodiment includes the
noise reduction processing unit 51 in place of the noise reduction processing unit 17 in the
stereo microphone of the first embodiment. It has the same configuration as the device 10.
Therefore, in the present embodiment, only the noise reduction processing unit 51 will be
described, and the other parts will be assigned the same reference numerals and descriptions
thereof will be omitted. The noise reduction processing unit 51 extracts a signal of a touch noise
band from the signal output by the first A / D converter 15. A first noise band extraction unit 52
and a first noise band extraction unit 52: A first attenuator 53 for halving the signal output by
52, and a second noise band extraction for extracting a signal of a touch noise band from the
signal output by the second A / D converter 16 Unit 54, a second attenuator 55 which halves the
signal output by the second noise band extraction unit 54, a signal output by the first attenuator
53, and the second attenuator 55. A first adder 56 for adding the signal output by the first noise
filter 52 and a second adder for subtracting the signal output by the first adder 56 from the
signal output by the first noise band extraction unit 52 57 and the second noise And a third
adder 58 for subtracting the signal output by the first adder 56 from the signal output by the
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band extraction unit 54. Further, the noise reduction processing unit 51 is a first adaptive noise
reduction apparatus to which the signal output by the first A / D converter 15 and the signal
output by the second adder 57 are supplied. (Adaptive Noise Cancellar; hereinafter referred to as
ANC. And a second ANC 61 to which the signal output by the second A / D converter 16 and the
signal output by the third adder 58 are supplied. The signal output from the first ANC 60 and the
signal output by the second ANC 61 are supplied to the directional calculation processing unit
18. The microphone device 50 may not include the first noise band extraction unit 52 and the
second noise band extraction unit 54. When the first noise band extraction unit 52 and the
second noise band extraction unit 52 are not provided, noise generated in bands other than the
touch noise band can also be reduced. The noise reduction processing unit 51 performs the
calculation described below. First, the first attenuator 53 halves the signal Rs + Rn supplied by
the first A / D converter 15 to 1?2 (Rs + Rn).
The second attenuator 55 halves the signal Ls + Ln supplied by the second A / D converter 16 to
1?2 (Ls + Ln). Next, the first adder 56 performs an operation 11 shown below. 1/2 (Rs + Rn) +
1/2 (Ls + Ln) = 1/2 (Rs + Ls) + 1/2 (Rn + Ln) = 1/2 (Rs + Ls) = Rs = Ls Operation 11 Next, The
second adder 57 performs the operation 12 shown below. (Rs + Rn) -Rs = Rn. Operation 12 The
third adder 58 performs the operation 13 described below. (Ls + Ln) ?Ls = Ln Operation 13 In
the present embodiment, since the first noise band extraction unit 52 and the second noise band
extraction unit 54 are provided. The operations 11, 12, and 13 are performed only in the noise
band, but when the first noise band extracting unit 52 and the second noise band extracting unit
54 are not provided, the operations 11, 12, and 13 are performed. The operation 13 is
performed over the entire band of the audio signal. That is, the signal Rs + Rn and the vibration
noise Rn are supplied to the first ANC 60, and Ls + Ln and the vibration noise Ln are supplied to
the second ANC 61. The first ANC 60 performs a further operation on the signal Rs + Rn and the
vibration noise Rn to generate a noise-reduced signal for the right channel, and the second ANC
61 generates the signal Ls + Ln and the vibration noise Ln. Further operations are performed to
generate a noise-reduced signal for the left channel. The details of the calculation performed by
the first ANC 60 and the second ANC 61 will be described later. The first ANC 60 will be
described in detail below. The first ANC 60 adaptively controls the vibration noise Rn output
from the first delay unit 62 to which the signal is supplied from the first A / D converter 15 and
the second adder 57. First adaptive filter 63, and the signal output by the first delay filter 62 is
subtracted from the signal output by the first adaptive filter 63, and the result of subtraction is
the directional arithmetic processing unit 18 and the first And a fourth adder 64 for supplying to
the adaptive filter 63 of The first delay unit 62 controls the timing at which the signal output by
the first A / D converter 15 is supplied to the + terminal of the fourth adder 64.
More specifically, the first A / D converter 15 outputs a signal and supplies the signal to the first
delay unit 62 and the first noise band extraction unit 52. The first delay unit 62 receives the
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signal supplied to the first noise band extraction unit 52 as a first attenuator 53, a first adder 56,
a second adder 57, and a first adaptive filter 63. The supplied signal is held until it is supplied to
the-terminal of the fourth adder 64 via the. Then, the first delay unit 62 performs a fourth adder
64 on the signal held at the same timing as the signal is supplied from the first adaptive filter 63
to the negative terminal of the fourth adder 64. Supply to the + terminal of The first adaptive
filter 63 is also referred to as vibration noise Rn (hereinafter, referred to as a reference signal
X0) output by the second adder 57. And the signal output by the fourth adder 64 (hereinafter
also referred to as residual signal E). And adaptive filter processing is performed on the vibration
noise Rn to generate and output a pseudo noise signal Y1 having high correlation to the vibration
noise Rn. The details of the first adaptive filter 63 will be described later. The fourth adder 64
subtracts the pseudo noise signal Y1 having high correlation with the vibration noise Rn from the
signal Rs + Rn supplied by the first delay unit 62, thereby generating the vibration noise Rn and
the acoustic noise. Generate a signal R ? from which noise and noise have been removed. The
first adaptive filter 63 will be described in detail below. As shown in FIG. 10, the first adaptive
filter 63 performs an operation on the input reference signal X0 to generate and output a pseudo
noise signal Y1, and the input reference signal An LMS circuit 72 is provided to calculate
coefficients used in the calculation of the FIR filter 71 from X0 and the residual signal E. The FIR
filter 71 delays the input signal and outputs m (where m is an integer of 2 or more). Coefficients
calculated by the LMS circuit 72 for each of the delay devices 73-1, 73-2, ... 73-m, the reference
signal X0, and the signals output from the respective delay devices 73-1 to 73-m. And m + 1
multipliers 74-0, 74-1,... 74-m, and the signals output by the respective multipliers 74-0 to 74-m
are added to be correlated with the reference signal X0. And an adder 75 for generating and
outputting a high pseudo noise signal Y1. The delay units 73-2 to 73-m hold the signal output by
the delay unit provided one before, and delay the signal by a unit sampling time to output.
That is, the delay unit 73-h (where h is a natural number of 2 or more and m or less). ) Hold,
delay and output the signal output from the delay unit 73- (h-1). Also, the delay unit 73-1 holds
the reference signal X0, delays it by unit sampling time, and outputs it. Therefore, the reference
signal is X0, the signals output by the delay units 73-1 to 73-m are X1, X2, ... Xm, and the
coefficients of the multipliers 74-0 to 74-m are Assuming that W0, W1,... Wm, the pseudo noise
signal Y1 output from the adder 75 is calculated by a convolution operation as shown by the
following operation 21. The LMS circuit 72 calculates coefficients from the reference signal X0
and the residual signal E according to the LMS (Least Mean Square) algorithm. W0, W1, ... Wm
are calculated. Specifically, coefficients W0, W1,... Wm are calculated by performing the
following operation 22. <Img class = "EMIRef" id = "19818402-00004" /> where k is an integer. )
Indicates the sampling time has elapsed. That is, assuming that the coefficient Wk at the kth
sampling is the current coefficient, Wk-1 indicates the kth-1th sampling, that is, a coefficient in
the past at one sampling. Also, ? is a gain factor (step gain, step size) that determines the speed
and stability of adaptation. The LMS circuit 72 generates the pseudo noise signal Y1 highly
correlated with the reference signal X0 by performing the operation 21, and correlates with the
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vibration noise Rn included in the signal output by the fourth adder 64. Minimize high quality
signals. The algorithm used in the first adaptive filter 63 is not limited to the LMS algorithm.
However, since the convergence speed is relatively fast and the computation scale is small, the
LMS algorithm is often used. The calculation in the LMS circuit 72 can be processed by hardware
using a DSP (Digital Signal Processor) and digital LSI (Large Scale Integration) or software using a
microcomputer.
The second ANC 61 includes a second delay 81, a second adaptive filter 82, and a fifth adder 83.
The second delay 81 has a first delay. The second adaptive filter 82 corresponds to the first
adaptive filter 63, and the fifth adder 83 corresponds to the fourth adder 64. The second ANC 61
is the same as the first ANC 60 except that Ln and Ls + Ln are supplied instead of Rn and Rs + Rn,
and outputs the pseudo noise signal Y2 instead of the pseudo noise signal Y1. Therefore, the
detailed description of the second ANC 61 is omitted. The operation of the stereo microphone
device 50 will be described below. The operation until the A / D conversion of the signals
supplied by the first and second A / D converters 15 and 16 is the same as that of the stereo
microphone device 10, so the description will be omitted. The first A / D converter 15 supplies
the A / D converted signal to the first noise band extraction unit 52 and the first delay unit 62.
The second A / D converter 16 supplies the A / D converted signal to the second noise band
extraction unit 54 and the second delay unit 81. Next, the first noise band extraction unit 52
extracts the signal of the touch noise band from the signal supplied by the first A / D converter
15 and supplies the signal to the first attenuator 53. Further, the second noise band extraction
unit 54 extracts a signal of the touch noise band from the signal supplied by the second A / D
converter 16 and supplies the signal to the second attenuator 55. Next, the first attenuator 53
halves the signal supplied by the first noise band extraction unit 52 to generate 1?2 (Rs + Rn),
and the first adder 56 Supply to Further, the second attenuator 55 halves the signal supplied by
the second noise band extraction unit 54 to generate 1?2 (Ls + Ln) and supplies it to the first
adder 56. Next, the first adder 56 performs operation 11 to generate the audio signal Rs (= Ls),
and the ? terminal of the second adder 57 and the ? terminal of the third adder 58 Supply to
Next, the second adder 57 performs operation 12 to generate the vibration noise Rn, and
supplies the vibration noise Rn to the first adaptive filter 63. In addition, the third adder 58
performs the operation 13 to generate the vibration noise Ln, and supplies the vibration noise Ln
to the second adaptive filter 82. Next, the first adaptive filter 63 generates a pseudo noise signal
Y 1 from the supplied vibration noise Rn and supplies the pseudo noise signal Y 1 to the ?
terminal of the fourth adder 64.
Further, the second adaptive filter 82 generates a pseudo noise signal Y2 from the supplied
vibration noise Ln and supplies the pseudo noise signal Y2 to the-terminal of the fifth adder 83.
Next, the fourth adder 64 subtracts the pseudo noise signal Y1 from the signal supplied by the
first delay unit 62 to generate vibration noise from the signal Rs + Rn output by the first
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microphone 11. A signal having a high correlation with Rn is subtracted, that is, a signal R ?
from which the vibration noise Rn and the acoustic noise are removed. The signal R ? is
supplied to the directional calculation processing unit 18 and the first adaptive filter 63. In
addition, the fifth adder 83 subtracts the pseudo noise signal Y2 from the signal supplied by the
second delay unit 81, thereby correlating the signal Ls + Ln output from the second microphone
12 with the vibration noise Ln. Generates a signal L ? from which the high signal is subtracted,
that is, the vibration noise Ln and the acoustic noise are removed. The signal L ? is supplied to
the directional calculation processing unit 18 and the second adaptive filter 82. Finally, the
directional calculation processing unit 18 performs an operation on R ? to generate and output
an audio signal for the right channel, and performs an operation on L ? to perform an operation
on the left channel. Generate and output an audio signal of As described above, the noise
reduction processing unit 51 provided in the stereo microphone device 50 to which the present
invention is applied generates the vibration noise Rn and the vibration noise Ln by performing
the calculations 11, 12, and 13. . Then, an adaptive filter process is performed on Rn to generate
a pseudo noise signal Y1 correlated with Rn, which is subtracted from the signal Rs + Rn to
output an audio signal R ? in which the vibration noise Rn and the acoustic noise are reduced.
Further, by applying an adaptive filter process to Ln, a pseudo noise signal Y2 correlated with Ln
is generated and subtracted from the signal Ls + Ln to output an audio signal L ? with reduced
vibration noise Ln and acoustic noise. Therefore, the stereo microphone device 50 to which the
present invention is applied outputs two-channel audio with reduced vibration noises Rn and Ln
and acoustic noise even though two microphones are provided. It is possible to Further, in the
stereo microphone device 50 to which the present invention is applied, the first adaptive filter 63
generates a pseudo noise signal Y1 similar to the noise included in the signal Rs + Rn output by
the first microphone 11, The second adaptive filter 82 generates a pseudo noise signal Y2 similar
to the noise contained in the signal Ls + Ln output by the second microphone 12.
That is, since the stereo microphone device 50 to which the present invention is applied
processes the signal Rs + Rn and the signal Ls + Ln respectively with independent adaptive filters,
for example, noise included in the signal Rs + Rn and noise included in the signal Ls + Ln Even
when there is a phase difference or level difference between the two, noise can be reduced with
high accuracy. It is preferable that the stereo microphone device 50 also have the level
adjustment unit 30 between the first A / D converter 15 and the second A / D converter 16 and
the noise reduction processing unit 17. . The stereo microphone device 50 includes the level
adjustment unit 30 so that the level of the signal output by the first A / D converter 15 and the
level of the signal output by the second A / D converter 16 can be obtained. Since it becomes
possible to suppress the difference between the two, it becomes possible to improve the
calculation accuracy of the calculations 11, 12, and 13, and it becomes possible to reduce noise
with high accuracy. In the first embodiment, only the vibration noises Ln and Rn are reduced, but
in the second embodiment, they are included in the signals Ls and Rs in addition to the vibration
noises Ln and Rs. It is characterized in that acoustic noise correlated with Rn is simultaneously
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reduced. Third Embodiment Next, the third embodiment of the present invention will be
described in detail. As shown in FIG. 11, the stereo microphone device 100 of the present
embodiment includes the noise reduction processing unit 101 in place of the noise reduction
processing unit 51, except for the stereo microphone device 10 of the first embodiment. It has
the same configuration as Therefore, in the stereo microphone device 100 according to the
present embodiment, only the noise reduction processing unit 101 will be described, and the
other parts will be assigned the same reference numerals and descriptions thereof will be
omitted. The same parts as those of the stereo microphone device 50 of the second embodiment
are also assigned the same reference numerals and explanation thereof is omitted. The noise
reduction processing unit 101 outputs a third attenuator 102 that halves the signal output by the
first noise band extraction unit 52 and a second noise band extraction unit 54. A fourth
attenuator 103 that halves the signal, and a sixth adder 104 that subtracts the signal output by
the third attenuator 102 from the signal output by the fourth attenuator 103; A third delay 105
to which a signal is supplied from the first A / D converter 15, a signal output by the sixth adder
104 and a signal output by the third delay 105 are added. The seventh adder 106, the fourth
delay unit 107 to which a signal is supplied from the second A / D converter 16, and the signal
output by the fourth delay unit 107 are processed by the sixth adder 104. Second to subtract the
output signal And eight adders 108.
The third delay unit 105 controls the timing at which the signal output by the first A / D
converter 15 is supplied to the seventh adder 106. Specifically, first, the first A / D converter 15
outputs a signal and supplies the signal to the third delay unit 105 and the first noise band
extraction unit 52. Next, the third delay unit 105 supplies the signal supplied to the first noise
band extraction unit 52 to the seventh adder 106 via the third attenuator 102 and the sixth
adder 104. Hold the supplied signal until it is Then, the third delay unit 105 supplies the held
signal to the seventh adder 106 at the same timing as the signal is supplied from the sixth adder
104 to the seventh adder 106. . The fourth delay unit 107 controls the timing at which the signal
output by the second A / D converter 16 is supplied to the + terminal of the eighth adder 108.
Specifically, first, the second A / D converter 16 outputs a signal and supplies the signal to the
fourth delay unit 107 and the second noise band extraction unit 54. Next, the fourth delay unit
107 receives the signal supplied to the second noise band extraction unit 54 via the fourth
attenuator 103 and the sixth adder 104- Hold the supplied signal until it is supplied to the
terminal. Then, the fourth delay unit 107 receives the held signal at the + terminal of the eighth
adder 108 at the same timing as the timing at which the signal is supplied from the sixth adder
104 to the eighth adder 108. Supply to In the noise reduction processing unit 101, the third and
fourth attenuators 102 and 103 and the sixth adder 104 perform the operation 1, and the
seventh adder 106 performs the operation 2, and the eighth The adder 108 performs operation
3 to generate the signals Rs and Ls from which the vibration noises Rn and Ln have been
removed, and supply the signal Rs to the first delay device 62 provided in the first ANC 60, The
signal Ls is supplied to a second delay 81 provided in a second ANC 61. Hereinafter, the
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operation of the stereo microphone device 100 will be described. The operation until the A / D
conversion of the signals supplied by the first and second A / D converters 15 and 16 is the same
as that of the stereo microphone device 10, so the description will be omitted. The first A / D
converter 15 supplies the A / D converted signal to the first noise band extraction unit 52 and
the third delay unit 105. Also, the second A / D converter 16 supplies the A / D converted signal
to the second noise band extraction unit 54 and the fourth delay unit 107.
Next, the first noise band extraction unit 52 extracts the signal of the touch noise band from the
signal supplied by the first A / D converter 15, and the first attenuator 53, the second The plus
terminal of the adder 57 and the third attenuator 102 are supplied. Further, the second noise
band extraction unit 54 extracts the signal of the touch noise band from the signal supplied by
the second A / D converter 16, and the second attenuator 55 and the third adder 58 are
provided. The + terminal and the fourth attenuator 103 are supplied. Next, the first attenuator 53
halves the signal supplied by the first noise band extraction unit 52 to generate 1?2 (Rs + Rn),
and the first adder 56 Supply to Further, the second attenuator 55 halves the signal supplied by
the second noise band extraction unit 54 to generate 1?2 (Ls + Ln) and supplies it to the first
adder 56. Next, the first adder 56 performs operation 11 to generate Rs (= Ls), and supplies Rs
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