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JPH05316587

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DESCRIPTION JPH05316587
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
microphone device.
[0002]
2. Description of the Related Art For example, in a camera integrated VTR, while photographing
an object, the sound around the object is simultaneously recorded. In collecting the sound, it is
generally considered that only the sound from the direction of the subject is collected. That is, a
microphone device having directivity such that only sound from the front of the camera is picked
up is used.
[0003]
As an example of this type of microphone device, for example, a so-called gun microphone is
known. As shown in FIG. 10, this comprises a pipe portion 2 extending forward of the diaphragm
1. Then, a large number of through holes 3 are provided on the side wall of the pipe portion 2,
and the directivity is high in sensitivity to the sound from the front (the opposite direction to the
diaphragm) of the pipe portion 2 in the centerline direction. It is configured to have a sex.
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[0004]
That is, as shown in FIG. 10A, the sound wave from the front (right side of the figure) of the
microphone enters either from the tip of the pipe portion 2 or from the through hole 3 at any
position of the pipe portion 2, Since the path lengths to all reach the diaphragm 1 are the same,
they enter the diaphragm 1 in phase and are added to each other.
[0005]
On the other hand, as shown in FIG. 10B, the acoustic wave incident from the side of the pipe
portion 2 has a different path length from the incident position to the diaphragm 1 depending on
the position of the incident hole 3 and thus a phase difference occurs. .
Similarly, as shown in FIG. 10C, the sound wave from the back of the microphone also has a
phase difference in the signal incident on the diaphragm 1 due to the position of the hole 3 that
enters and wraps around. The plurality of holes 3 of the pipe portion 2 are formed at positions
where the incident voices weaken each other, and the microphone of FIG. 10 has directivity less
sensitive to voices from the side and back of the pipe. Have.
[0006]
As described above, according to the gun microphone of FIG. 10, a directional microphone
having high sensitivity to voice from the front of the microphone can be obtained.
[0007]
However, this microphone requires the long pipe portion 2 and has the drawback of becoming
large.
In addition, it is unidirectional with high sensitivity only in front of the microphone, and only
fixed directivity can be obtained. Therefore, it is difficult to cope with the case where voices from
not only the voice from the desired voice arrival direction but also voices from the side around
the camera are to be picked up, for example, and there is no freedom in the direction of
directivity.
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[0008]
In view of the above, it is an object of the present invention to provide a microphone device
which is compact and can easily obtain desired directivity.
[0009]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a microphone
device according to the present invention comprises: a first microphone 11 for picking up a
desired voice when the reference numerals of the embodiments described later correspond to
each other; From the voice signal of the first microphone 11, the adaptive filter means from the
second microphone 21 of directivity with low sensitivity to the desired voice arrival direction, the
adaptive filter means 24 to which the voice signal from the second microphone 21 is supplied,
and The present invention is characterized in that the adaptive filter means 24 is adjusted such
that the output power of the subtraction means 15 is minimized.
[0010]
In the above-described configuration, the directivity of the second microphone 21 has low
sensitivity in the direction of arrival of the desired voice.
When the arrival directions of the input voices to be collected are different, the sound sources
are different and the correlations are often small.
Therefore, there is little correlation between the sound signal from the second microphone and
the desired sound from the first microphone 11. Therefore, when the sound signal from the
second microphone 21 is considered as noise, the microphone device of the present invention
becomes a configuration of an adaptive noise reduction system, and when the output power of
the subtraction means is minimized, the second microphone 21 Is removed from the audio signal
from the first microphone 11, and only the desired audio from the first microphone 11 is output
voice signal.
[0011]
That is, the microphone device of the present invention has a configuration of an adaptive noise
reduction system in which desired voice and noise are distinguished according to the direction of
arrival of voice, and by considering the directivity of the second microphone 21, desired voice A
microphone device having sensitivity in the direction of arrival is obtained.
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[0012]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the microphone
device according to the present invention will be described below with reference to FIG.
In FIG. 1, reference numeral 11 denotes a main input microphone for collecting desired voice,
and reference numeral 21 denotes a reference input microphone for collecting voice in a
direction to be removed as noise. In this example, the arrival direction of the desired voice is a
direction (hereinafter referred to as a front direction) going from the top to the bottom on the
figure mainly as shown by an arrow AR in FIG. This is an example of realizing a microphone
device that prevents voices from the voices) from being picked up as noise.
[0013]
In the case of this example, the main input microphone 11 is configured by an omnidirectional
microphone as shown in FIG. On the other hand, as shown in FIG. 2, the reference input
microphone 21 is composed of a unidirectional microphone having no sensitivity in the desired
voice incoming direction but having sensitivity only in the back direction.
[0014]
Then, an audio signal picked up by the main input microphone 11 and converted into an electric
signal is obtained through the amplifier 12 and supplied to the A / D converter 13, converted
into a digital signal, and the delay circuit 14. The signal is supplied to the subtraction circuit 15
via
[0015]
Further, an audio signal obtained by being picked up by the reference input microphone 21 and
converted into an electric signal is supplied to the A / D converter 23 through the amplifier 22
and converted into a digital signal, and the adaptive filter circuit 24 is obtained. Supplied to
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Then, the output signal of the adaptive filter circuit 24 is supplied to the subtraction circuit 15.
The output signal of the subtraction circuit 15 is fed back to the adaptive filter circuit 24 and
also converted back to an analog signal by the D / A converter 16 and is led out to the output
terminal 17.
[0016]
The audio signal may be output as it is without passing through the D / A converter 16. The
delay circuit 14 is for compensating for the time delay required for the calculation for the
adaptive processing in the adaptive filter circuit 24, the propagation time in the adaptive filter,
and other time delays.
[0017]
In the adaptive filter circuit 24, as described later, the reference input speech is controlled to
approximate to the speech as noise contained in the main input speech. Thereby, assuming that
the desired voice in the voice collected by the main input microphone 11 and the noise are
uncorrelated, in the subtraction circuit 15, the noise signal collected by the reference input
microphone 21 is the main input The voice signal from the microphone 11 is subtracted and
removed, and only the desired voice is obtained from the subtraction circuit 15.
[0018]
That is, this configuration is the configuration of an adaptive noise reduction system in which the
output sound signal of the main input microphone 11 is supplied as the main input and the
output sound signal of the reference input microphone 21 is supplied as the noise as the
reference input. ing. The operation of this system will now be described.
[0019]
In this case, the main input audio signal from the A / D converter 13 is a desired audio signal s
from the front direction of the arrow AR and an audio signal from the rear direction considered
to be uncorrelated with this (hereinafter referred to as noise ) N0 is added. On the other hand,
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assuming that the reference input audio signal from the A / D converter 23 is n1, as is clear from
the above description, the reference input audio signal n1 is uncorrelated with the desired audio
signal, but with the noise n0 There is a correlation. The adaptive filter circuit 24 filters the
reference input speech signal n1 to output a signal y, and the adaptive algorithm works to
minimize the subtraction error e which is the output of the subtraction circuit 15.
[0020]
Now, assuming that s, n0, n1, and y are statistically stationary and the average value is 0, the
output is e = s + n0-y. Since the expected value of the square of this is uncorrelated with s and n0
and y, E [e2] = E [s2] + E [(n0-y) 2] + 2E [s (n0-y) ] = E [s2] + E [(n0-y) 2]. Assuming that the
adaptive filter circuit 24 converges, the adaptive filter circuit 24 is adjusted to minimize E [e2]. At
this time, since E [s2] is not affected, Emin [e2] = E [s2] + Emin [(n0-y) 2]. That is, E [(n0-y) 2] is
minimized by minimizing E [e2], and the output y of the adaptive filter circuit 24 becomes an
estimate of the noise n0. The expected value of the output from the subtraction circuit 15 is only
the desired signal. That is, adjusting the adaptive filter circuit 24 to minimize the total output
power is equal to the subtraction output e being the least squares estimate of the desired speech
signal s.
[0021]
One example of the adaptive filter circuit 24 is shown in FIG. 3 as an adaptive algorithm in the
case of using the so-called LMS (least mean square) algorithm.
[0022]
As shown in FIG. 3, in this example, an adaptive linear combiner 300 of FIR filter type is used.
This includes a plurality of delay circuits DL1, DL2,... DLm (m is a positive integer) each having a
delay time Z-1 of unit sampling time, an input signal n1 and each delay circuit DL1, DL2,. , And
an adder circuit 310 for adding the outputs of the weight circuits MX0 to MXm. The output of
the summing circuit 310 is y.
[0023]
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Weighting coefficients to be supplied to the weighting circuits MX0 to MXm are formed from the
residual signal e from the subtraction circuit 15 by the LMS operation circuit 320 comprising, for
example, a microcomputer. The algorithm executed by this LMS arithmetic circuit 320 is as
follows.
[0024]
Now, let the input vector Xk at time k be Xk = [x0k x1k x2k ... xmk] T, as also shown in Fig. 3, the
output yk, the weighting factor wjk (j = 0, 1, 2, ... Assuming that m), the input / output
relationship is as shown in the following equation 1:
[0026]
Then, if the weight vector Wk at time k is defined as Wk = [w0k w1k w2k... Wmk] T, the input /
output relation is given by yk = Xk T · Wk.
Assuming that the desired response is dk, the error ek with the output is expressed as follows. In
the ek = dk-yk = dk-Xk T · WkLMS method, updating of the weight vector is performed according
to the formula Wk + 1 = Wk + 2μ · ek · Xk. Here, μ is a gain factor (step gain) that determines
the speed and stability of adaptation.
[0027]
Thus, at the output terminal 17, an audio signal consisting mainly of the desired audio signal
from which noise, in this example, the audio signal from the back direction, has been removed is
obtained.
[0028]
By the way, in order to reduce the noise in the main input using the reference input by the
adaptive processing as described above, it is necessary for the desired voice and the reference
noise to be uncorrelated, as described above.
For this reason, conventionally, in this type of adaptive noise reduction system, the reference
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input microphone is specially designed for sound proofing, or placed as close as possible to the
noise source so as not to pick up the desired voice as the reference input. Measures such as
keeping away from the input microphone have been taken. However, this makes the system large
and difficult to move.
[0029]
On the other hand, in the case of the present invention, desired voice and noise are distinguished
according to the direction of arrival of voice. The main input microphone 11 is configured to
have directional characteristics (including non-directionality) that can pick up voice from the
desired voice arrival direction, and the reference input microphone 21 is configured in the
desired voice arrival direction. As a configuration having no sensitivity or low sensitivity
directivity, the desired voice in the sound collected by the main input microphone 11 and the
noise collected by the reference input microphone 21 are uncorrelated. It is like that.
[0030]
Therefore, in the case of the present invention, only the directivity of the main input microphone
and the reference input microphone need be considered, and both microphones can be disposed
close to each other, which is smaller than the conventional microphone system. You can
[0031]
And by the configuration of the present invention, the noise signal is well removed from the main
input, and as a result, it is possible to easily realize a directional microphone device having low
sensitivity or no sensitivity in the noise input arrival direction.
FIG. 4 is a figure for showing what confirmed the effect in the case of this example
experimentally.
[0032]
That is, as shown in FIG. 2, in this experimental apparatus, the desired voice arrival direction is
the direction of arrow AR, and the main input microphone 11 and the reference input
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microphone 21 are desired with the main input microphone 11 in front. Arranged back and forth
along the voice incoming direction. Then, for example, a sine wave signal of 1 kHz is made to
come from the direction of the arrow AR as desired voice, and a sine wave of 600 Hz is made to
come as noise from the direction of the back face and 30 °, for example. Do.
[0033]
In this example, the sensitivity of the omnidirectional main input microphone 11 is 0 dB, the
reference input microphone 21 is -20 dB for voice from the front, and the sensitivity in the back
direction is 0 dB, from a direction of 30 ° from the back The sensitivity to input speech is -0.7
dB.
[0034]
At this time, the input waveform of the main input microphone 11 is a combination of a 1 kHz
sine wave and a 600 Hz sine wave as shown in FIG. 4A, but the output voice waveform obtained
at the output terminal 17 is As shown in FIG. 4B, the output ideal waveform shown in FIG. 4C is
approximated to a 1 kHz sine wave, and the effect of the microphone device according to the
present invention can be confirmed.
[0035]
FIGS. 5 and 6 show examples of directivity characteristics of the main input microphone 11 and
the reference input microphone 21 in another embodiment of the microphone device according
to the present invention.
Also in these examples, with the desired voice arrival direction as the direction of arrow AR, the
main input microphone 11 and the reference input microphone 21 are front and back along the
desired voice arrival direction with the main input microphone 11 in front. Place on
[0036]
In the example of FIG. 5, the main input microphones 11 are arranged in a single direction with
the highest sensitivity in the front direction.
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In addition, the reference input microphone 21 is unidirectionally arranged, for example, with the
highest sensitivity directed in the back direction. That is, the reference input microphone 21 has
a low sensitivity in the arrival direction of the desired voice, and a high sensitivity in the back
direction, which is the arrival direction of the noise signal in this example.
[0037]
Therefore, also in the case of this example, it is possible to realize the microphone device that
obtains only the desired voice as the output in the same manner as described above. Then, in the
case of this example, assuming that the noise signal comes between approximately 90 degrees
from the back direction, this direction is a direction in which the main input microphone 11 is
also low in sensitivity. Noise level is lower. Therefore, the main input microphone 11 itself has a
noise reduction effect.
[0038]
The example of FIG. 6 is an example in the case where it is desired to limit the arrival direction of
noise to be removed to near the 90 degree direction of the desired voice arrival direction or to
increase the sensitivity of the reference input microphone in the 90 degree direction. In the case
of this example, the directivity characteristic of the reference microphone 21 is bi-directional
(eight-character directivity) as illustrated. As in the example of FIG. 5, the main input
microphones 11 are unidirectional so that the desired voice direction is arranged to have the
highest sensitivity. However, also in this example, the main input microphone 11 may be
omnidirectional.
[0039]
The above example is the case where the main input microphone 11 and the reference input
microphone 21 use a single microphone unit whose directional characteristic is the directional
characteristic as described above, and a plurality of microphone units may be used as these
microphones. It is possible to use a type that realizes a microphone with desired directivity.
[0040]
An example of realizing a unidirectional microphone by using two nondirectional microphone
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units will be described with reference to FIGS. 7 and 8.
As shown in FIG. 7, in this example, the omnidirectional microphone units 30 and 31 are spaced
apart by a distance d. Then, as shown in FIG. 8, the output sound signal of one microphone unit
30 is supplied to the subtraction circuit 32 via an amplifier (not shown). The output sound signal
of the other microphone unit 31 is supplied to the subtraction circuit 32 through an amplifier
and filter circuit 33 which is also omitted from the drawing. The filter circuit 33 is composed of a
resistor 34 and a capacitor 35 in this example. Then, when the resistance value of the resistor 34
is R1 and the capacitance of the capacitor 35 is C1, the resistance value R1 and the capacitance
C1 are selected such that C1 · R1 = d / c (where c is the speed of sound). ing.
[0041]
Then, in this example, an output sound signal is derived from the output of the subtraction circuit
32 to the output terminal 37 through the frequency characteristic correction circuit 36 such as
an integrator for flattening the frequency characteristic. As will be described later, the frequency
characteristic correction circuit 36 is provided as necessary, and may not be provided.
[0042]
The operation of the microphone of this example will be described. As shown in FIG. 7, when the
sound source is in the direction of an angle θ with respect to the arrangement direction of the
two microphone units 30 and 31 and is incident on these two microphone units 30 and 31.
Assuming that the outputs of the units 30 and 31 are P0 and P1, the output P1 is P1 = P0
.epsilon.-j.omega. (D / c) cos .theta. Here, ω is an angular frequency.
[0043]
Since the output of the microphone unit 31 is supplied to the subtraction circuit 32 through the
filter circuit 33, the output signal Pa of the subtraction circuit 32 is as shown in the following
equation 2.
[0044]
In Expression 2, A represents the filter function of the filter circuit 33, and ω · d / c << 1.
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[0045]
Then, in the equation (2), if the following equation (3) is satisfied, the output Pa shows unidirectionality.
[0046]
That is, when the following equation 3 is satisfied, the equation 2 becomes Pa = P0jω (d / c) (1 +
cos θ), and becomes unidirectional with respect to the angle θ.
[0047]
In the above example, the filter function A of the filter circuit 33 is represented by A = 1 / (1 +
jωC1 · R1), and C1 · R1 = d / c. Therefore, A = 1 It is clear that the microphone of the
embodiment of FIG. 7 becomes uni-directional, as / (1 + jωd / c).
However, the frequency characteristic of this microphone is an upward rightward characteristic
(the higher the frequency, the larger the response).
In this example, a frequency characteristic correction circuit 36 is provided to correct this
upward-smooth characteristic.
[0048]
In the example of FIG. 8, the filter circuit 33, the subtraction circuit 32, and the frequency
characteristic correction circuit 36 can also be realized by a digital filter or a processing program
(software).
[0049]
For example, as shown in FIG. 9, the filter circuit 33 can be configured by a digital filter including
an adder 41, a delay circuit 42, and a feedback amplifier 43 of transfer function A.
[0050]
In the above example, the microphone device of the present invention has been described as the
case of the sound pickup microphone device of the camera integrated type VTR, but the present
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invention is not limited to this example, and it is needless to say The present invention is
applicable to all microphone devices such as video cameras for video and microphone devices for
measurement.
[0051]
In the above example, since the adaptive filter circuit 24 is configured as a digital circuit, the
entire configuration is a digital circuit. However, the adaptive filter circuit 24 can be an overall
analog circuit configuration as an analog circuit configuration. It is.
In addition, only the adaptive filter circuit portion may be configured to be digital.
[0052]
As described above, according to the present invention, it is possible to realize a microphone
device having desired directivity characteristics only by changing the directivity characteristics of
the first and second microphones.
In particular, the directivity characteristic of the microphone device can be changed only by
changing the second microphone to a microphone having a different directivity characteristic,
and there is a feature that the degree of freedom of the directivity characteristic that can be
realized is large.
For this reason, since it can respond to various uses, a practical effect has a remarkable thing.
[0053]
Further, according to the present invention, the first and second microphones can be disposed
relatively close to each other, and there is no need to form a special shape such as a gun
microphone, so that a compact microphone device can be obtained.
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