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DESCRIPTION JP2008060625

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DESCRIPTION JP2008060625
PROBLEM TO BE SOLVED: To eliminate the difference in sensitivity between two microphones on
the left and right in a stereo recording device, and eliminate the need for a special adjustment
circuit and the like. SOLUTION: An adaptive filter 5 is constructed by using outputs of left and
right two microphones L-Mic and R-Mic as a main signal and a reference signal, and all frequency
components such as white noise from a sound source equidistant from two microphones. The
adaptive filter processing is performed in a state where the voice including T is generated, and
the filter coefficient when the output of the adaptive filter 5 becomes the minimum is held. Then,
at the time of normal recording, by passing the filter coefficient filter to the microphone output
corresponding to the reference signal, two microphone signals with a small difference in
sensitivity are obtained. [Selected figure] Figure 2
Stereo sound recording apparatus and microphone sensitivity difference correction method
[0001]
The present invention relates to a stereo sound recording apparatus for recording stereo sound
such as, for example, a voice recorder, a video camera, and a digital still camera, and a
microphone sensitivity difference correction method used for the stereo sound recording
apparatus.
[0002]
Devices that record stereo sound require two microphones with uniform input sensitivity.
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However, there are some problems in obtaining two microphones with the same input sensitivity.
That is, since there are variations in parts, variations due to assembly, and the like in
microphones that are mass-produced products, sorting work is required to prepare two
microphones with uniform input sensitivity, but this is not realistic.
[0003]
For this reason, it has been a common practice to newly provide a sensitivity difference
adjustment circuit comprising an amplifier, an output detector, a control means, etc. to adjust the
level on the left and right so that the sensitivity difference is reduced for each individual
microphone. (See, for example, Patent Document 1).
[0004]
In addition, as a stereo sound recording device, as a device for suppressing a noise component
included in an input signal by generating a main signal and a noise reference signal using two
microphones, a structure using an adaptive filter is proposed. (See, for example, Patent Document
2).
[0005]
JP, 2005-117486, A JP, 2004-187, 283 A
[0006]
However, in order to reduce the difference in sensitivity between the left and right microphones
in this way, the structure provided with a new adjustment circuit not only complicates the
structure and increases the cost, but also takes time and effort for adjustment, and adjusts the
necessary difference in sensitivity. It is hard to say that we can do this reliably, and it is desirable
to take some measures.
[0007]
In addition, although there is one in which an adaptive filter is provided to suppress the noise
component contained in the input signal, it is only that, which does not lead to elimination of the
sensitivity difference between the left and right microphones in stereo recording. It was
necessary to provide a circuit.
[0008]
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The present invention has been made in view of the above circumstances, and it is a stereophonic
audio recording system having a simple structure capable of eliminating the difference in
sensitivity between the right and left microphones and eliminating the need for special
adjustment circuits and the like. An object of the present invention is to obtain a microphone
sensitivity difference correction mechanism and a microphone sensitivity difference correction
method of a recording device.
[0009]
A stereo audio recording apparatus according to the present invention (inventions according to
claims 1 and 8) is a stereo audio recording apparatus for recording audio signals input from two
left and right microphones as stereo audio in order to meet such an object. Audio from an audio
signal from one of the microphones, a filter coefficient storage unit for storing the coefficients of
the adaptive filter, and a sound from a sound source equidistant from the two microphones at the
time of sensitivity difference correction. In the state where is generated, the adaptive filter is
performed by using the audio signal from one microphone as the main signal and the audio
signal from the other microphone as the reference signal, and the filter coefficients at the
convergence point are The filter coefficients are stored in the filter coefficient storage unit, and
in the normal recording, the filter coefficients are stored in the adaptive filter. Load the filter
coefficient from the presence unit, characterized by comprising an adaptive filter control unit to
be used as a fixed filter.
[0010]
A stereo sound recording apparatus according to the present invention (inventions according to
claims 2 and 9) is the stereo sound recording apparatus according to claim 1 described above,
further comprising a built-in speaker located equidistant from the two left and right
microphones, The adaptive filter control unit is characterized in that pseudo white noise is
generated from the built-in speaker at the time of sensitivity difference correction, and adaptive
processing of the adaptive filter is executed in a state where the pseudo white noise is generated.
[0011]
A stereo sound recording apparatus according to the present invention (inventions according to
claims 3 and 10) is the stereo sound recording apparatus according to claim 1 described above,
wherein sampling is performed to control a sampling frequency for sampling an audio signal
input from the microphone. The adaptive filter control unit executes sensitivity difference
correction processing for each changeable sampling frequency at the time of sensitivity
difference correction, and the filter coefficient storage unit performs filter coefficients
corresponding to each sampling frequency. In the normal recording, the filter coefficient storage
unit selects and uses the filter coefficient corresponding to the current sampling frequency.
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[0012]
A stereo sound recording apparatus according to the present invention (the invention according
to claim 4) is the stereo sound recording apparatus according to claim 1 described above,
wherein the adaptive filter control unit is configured to execute the instruction operation of
sensitivity correction by a user. It is characterized in that processing at the time of sensitivity
difference correction is performed.
[0013]
A stereo sound recording apparatus according to the present invention (the invention according
to claim 5) is the stereo sound recording apparatus according to claim 1 described above, in
which the adaptive filter control unit detects an environmental change affecting the microphone
sensitivity. The present invention is characterized in that the process at the time of the sensitivity
difference correction is performed.
[0014]
A stereo sound recording apparatus according to the present invention (the invention according
to claim 6) is the stereo sound recording apparatus according to claim 1 described above,
wherein the sound signal from the microphone on the side where the adaptive filter is not
inserted is used. It is characterized by inserting a delay device.
[0015]
A stereo sound recording apparatus according to the present invention (the invention according
to claim 7) is the stereo sound recording apparatus according to claim 1 described above,
wherein the sound signal from the microphone on the side where the adaptive filter is not
inserted is used. A noise removal filter may be inserted, and the adaptive filter control unit may
cause the adaptive filter to learn the characteristics of the noise removal filter in addition to the
sensitivity difference between the left and right.
[0016]
As described above, according to the stereo sound recording apparatus of the present invention,
an adaptive filter is inserted into an audio signal from one of the microphones, and an adaptive
filter in which two microphone outputs are used as a main signal and a reference signal is
configured. And adaptive processing is performed in a state in which sound including all
frequency components such as white noise is generated from a sound source equidistant from
two microphones, and the filter when the output of the adaptive filter becomes minimum (when
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converged) By holding the coefficients and passing the adaptive filter loaded with the held filter
coefficients during normal recording to the audio signal from one of the microphones, it is
possible to obtain two microphone signals with a small difference in sensitivity.
[0017]
Therefore, according to the present invention, it is not necessary to newly add an adjustment
circuit for the sensitivity difference correction of the two microphones, and although it has a
simple structure, two sensitivity differences do not occur. There is an excellent effect that a
microphone can be obtained.
[0018]
Further, according to the present invention, the stereo recording device incorporates a speaker at
a location equidistant from the two microphones, and generates white noise from the speaker
when executing the adaptive filter. There is an advantage that it is not necessary to use a special
jig, particularly an external sound source, for the sensitivity difference correction.
[0019]
Furthermore, according to the present invention, sensitivity difference correction processing is
executed for each changeable sampling frequency by the sampling frequency control unit that
controls the sampling frequency of the AD converter, and filter coefficients corresponding to
each sampling frequency are filter coefficients. Since the filter coefficient corresponding to the
current sampling frequency is selected and used from the filter coefficient storage unit during
normal recording, the sensitivity difference between the two microphones is eliminated and the
function as a stereo recording device is realized. It has the advantage of being able to
demonstrate.
[0020]
FIGS. 1 and 2 are a block diagram and a flowchart for explaining an embodiment of a
microphone sensitivity difference correction mechanism and a microphone sensitivity difference
correction method of a stereo sound recording apparatus according to the present invention.
[0021]
In these figures, first, the configuration of the device of the present invention will be described
below with reference to the block diagram of FIG.
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That is, the stereo sound recording apparatus according to the present invention includes the
microphones L-Mic and R-Mic on the left and right.
Then, in the normal operation (recording operation), the sound input from the microphone L-Mic
of the left channel is converted into a digital signal by the AD converter 1 performing sampling at
a sampling period specified by the sampling frequency control unit. After that, an appropriate
delay (a delay equal to the delay by the adaptive filter) is given by the delay unit 3, and the signal
is input to the audio data recording unit 4 and recorded as the left audio signal.
At the same time, the sound input from the right channel microphone R-Mic is converted into a
digital signal by the AD converter 2 at a sampling period specified by the sampling frequency
control unit, and then stored in the filter coefficient storage unit 9 The adaptive filter 5 performs
filter processing according to the existing filter coefficient, and is input to the audio data
recording unit 4 and recorded as the right audio signal.
[0022]
Also, in the sensitivity difference correction operation (the learning operation of the adaptive
filter), the sound input from the microphone L-Mic of the left channel is converted to a digital
signal by the AD converter 1 and then the main signal input of the adaptive filter 5 (d ).
At the same time, the sound input from the right channel microphone R-Mic is converted into a
digital signal by the AD converter 2 and becomes a reference signal (x) of the adaptive filter 5.
Then, a subtraction signal (e), which is the difference between the main signal input (d) and the
adaptive filter output, is output by the signal subtraction unit 6, and the adaptive filter 5 is
controlled according to the control of the adaptive filter control unit 8. The coefficients of the
adaptive filter 5 are updated so as to minimize the root mean square, and the updated filter
coefficients are stored in the filter coefficient storage unit 9.
The specific configuration and operation principle inside the adaptive filter is a general technique
as well known in the above-mentioned patent documents and the like, and thus detailed
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description will be omitted. An adaptive filter control unit is configured to learn and update filter
coefficients in accordance with an adaptive algorithm such as LMS algorithm.
[0023]
The operation of the device according to the invention will now be described by means of the
flow chart of FIG.
Although the operation based on the flowchart of FIG. 2 is mainly executed by the adaptive filter
control unit 8, the adaptive filter control unit 8 may be configured only by an electronic circuit,
or a program (not shown) by a CPU is used. It may be configured to perform control by
executing.
First, the sensitivity difference correction process will be described.
A sound source for sensitivity difference correction is installed at an equal distance from the two
microphones L-Mic and R-Mic of the voice input device, and a sound including all frequency
components such as white noise is generated.
Then, after the user performs an instruction operation to start the sensitivity correction
operation, the sampling frequency of the sampling frequency control unit is set to the first
frequency among the plurality of sampling frequencies that can be set by the device.
In this state, the learning operation of the filter coefficient by the adaptive filter 5 is started.
During the learning operation, for example, the coefficients of the adaptive filter configured by
the FIR digital filter are repeatedly updated according to the LMS algorithm and gradually
converge.
(S1)。
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Then, it is determined whether a predetermined time for the adaptive filter 5 to converge has
elapsed (S1-1), and when the predetermined time has elapsed, the learning operation of the
adaptive filter 5 is stopped (S2).
[0024]
At this time, the coefficients of the adaptive filter 5 are adjusted so that the sensitivity difference
between the two microphones L-Mic and R-Mic is minimized over all frequency bands.
The coefficients at this time are stored in the filter coefficient storage unit 9 as filter coefficients
corresponding to the set sampling frequency (S3).
[0025]
Normally, the audio recording device can adjust the recording time by changing the sampling
frequency, but if the sampling frequency changes, the coefficients (characteristics) of the
adaptive filter 5 also change. It is necessary to store filter coefficients corresponding to
frequencies.
Therefore, it is determined whether or not the processing has been performed for all sampling
frequencies (S8), and when the processing is performed for all sampling frequencies, the
sensitivity correction processing is ended, and all the samplings are still performed. If processing
has not been performed on the frequency, the sampling frequency is changed to the next
sampling frequency (S4), the processing from step S1 is repeated again, and a filter coefficient
corresponding to the new sampling frequency is determined. Save to
[0026]
Next, the case of the normal recording operation will be described.
After the user instructs to start recording, the filter coefficient stored in the filter coefficient
storage unit 9 is loaded to the adaptive filter 5 corresponding to the current sampling frequency
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set in the sampling frequency control unit. (S5).
[0027]
Next, the filter updating operation of the adaptive filter 5 is stopped and the adaptive filter 5 is
operated as a fixed filter (S6).
As a result, the sound input from the left channel microphone L-Mic is converted to a digital
signal by the AD converter 1 performing sampling at a sampling period specified by the sampling
frequency control unit, and then the delay device 3 properly adjusts the sound. Delay is input to
the audio data recording unit 4 and sequentially recorded as an audio signal on the left side. At
the same time, the sound input from the right channel microphone R-Mic corresponds to the
sampling frequency set after being converted to a digital signal by the AD converter 2 at the
sampling period specified by the sampling frequency control unit. Also, the adaptive filter 5
performs filter processing in accordance with the filter coefficient whose sensitivity difference
has been corrected, and is input to the audio data recording unit 4 to be recorded as an audio
signal on the right side. Then, by continuing this recording operation until the user instructs the
end of recording, the voice recording unit receives signals of the same level and the same
frequency characteristics from the left and right microphones L-Mic and R-Mic. And recorded in
the external or internal recording medium in the audio data recording unit 4.
[0028]
<Modification 1> In the above embodiment, the sensitivity difference correction process is
performed by generating white noise from the sound source outside the voice recording device,
but as shown in FIG. Three microphones L-Mic and R-Mic are set at equal distances, and a
random number generator 11 shown in FIG. 3 is added to generate data obtained by converting
random number data into an analog signal by the DA converter 13 The sensitivity difference
correction process may be performed by the white noise generated. Reference numeral 12
denotes a random number generator control unit. In this first modification, in addition to
performing sensitivity correction in response to a user's instruction operation of sensitivity
correction, the device automatically detects an environmental change that affects the microphone
sensitivity such as an elapsed time since the previous sensitivity correction and a temperature
change. And perform sensitivity correction.
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[0029]
Further, in the voice recording apparatus provided with the microphone sensitivity difference
correction mechanism according to the configuration of the first modification, there is no need to
additionally provide an adjustment circuit for correction of the sensitivity difference as in the
prior art. This provides an advantage that it is not necessary to use a jig such as an external
sound source for the purpose of difference correction.
[0030]
<Modification 2> In the above embodiment, the audio signal input from the left channel
microphone R-Mic and converted into a digital signal by the AD converter 1 is input to the delay
unit 3. A removal filter may be used.
In the second modification, the adaptive filter 5 not only corrects the sensitivity difference
between the left and right, but also learns the filter coefficient so as to perform noise removal of
the same characteristic as the noise removal filter on the left side. In the voice recording
apparatus provided with the microphone sensitivity difference correction mechanism according
to the configuration of the second modification, it is not only necessary to additionally provide an
adjustment circuit for correction of the sensitivity difference, but also the number of noise
removal filters is reduced. Play an advantage that can be The present invention is not limited to
the structure described in the above-described embodiment, and the shape, structure, and the
like of the stereo sound recording apparatus and the parts constituting the microphone
sensitivity difference correction mechanism may be appropriately modified or changed. It's too
late.
[0031]
For example, although the case where the adaptive filter 5 is provided on the microphone R-Mic
side of the right channel has been described in the above embodiment, the present invention is
not limited to this, the left microphone L-Mic or the left and right microphones L Needless to say,
it may be configured to be provided to both Mic and R-Mic.
[0032]
It is a block diagram for demonstrating the microphone sensitivity difference correction
mechanism of the stereo sound recording apparatus based on this invention.
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5 is a flowchart for explaining a microphone sensitivity difference correction method of the
stereo sound recording apparatus according to FIG. 1; The modification of the microphone
sensitivity difference correction mechanism of the stereo sound recording apparatus based on
this invention is shown, (a) is a block diagram of the mechanism relevant to a microphone, (b) is
a block diagram of the mechanism relevant to a speaker. It is a figure which illustrates the
modification of the microphone sensitivity difference correction method of the stereo sound
recording apparatus based on this invention, Comprising: It is a figure which shows the state
which left-and-right microphone L-Mic and R-Mic equidistantly from the speaker.
Explanation of sign
[0033]
1, 2 ... 1st, 2nd AD converter, 3 ... delay device, 4 ... voice data recording unit, 5 ... adaptive filter,
6 ... signal subtraction unit, 7 ... sampling frequency control unit, 8 ... adaptive filter control unit ,
9: filter coefficient storage unit, 11: random number generator, 12: random number generator
control unit, 13: DA converter, L-Mic, R-Mic, left and right microphones.
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