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DESCRIPTION JP2017188762

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DESCRIPTION JP2017188762
Abstract: To achieve stable level difference correction. A level difference correction apparatus
according to the present invention performs level difference correction of a plurality of acoustic
signals collected by a plurality of microphones. The level difference correction device of the
present invention includes a low pass filter, a low frequency time average power calculation unit,
a power ratio calculation unit, and a gain adjustment unit. The low pass filter passes only a
predetermined low frequency signal for each sound signal, and outputs a plurality of low
frequency sound signals. The low frequency time average power calculation unit obtains low
frequency time average power which is time average power for each low frequency acoustic
signal. The power ratio calculation unit obtains, for each of the low frequency time average
powers, a ratio to the reference power obtained from the low frequency time average power by a
predetermined means, and uses it as the power ratio. The gain adjustment unit adjusts the gain of
each acoustic signal based on the power ratio. [Selected figure] Figure 1
Level difference correction apparatus, level difference correction method, level difference
correction program, and recording medium
[0001]
The present invention relates to a level difference correction device for sound signals collected
by a plurality of microphones, a level difference correction method, a level difference correction
program, and a recording medium therefor.
[0002]
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1
As a prior art, the technique of nonpatent literature 1 is known.
FIG. 9 shows the configuration of the level difference correction device disclosed in Non-Patent
Document 1. As shown in FIG. The level difference correction device 900 performs level
difference correction of a plurality of acoustic signals collected by a plurality of microphones.
The level difference correction apparatus 900 includes time average power calculators 920 1 to
920 N, an average value calculator 935, power ratio calculators 930 1 to 930 N, and gain
adjusters 140 1 to 140 N. The time average power calculators 920 1 to 920 N obtain time
average power which is time average power for each acoustic signal. The average value
calculation unit 935 obtains all channel average power which is an average of all time average
powers. The power ratio calculators 930 1 to 930 N calculate the ratio to the total channel
average power for each time average power, and use it as the power ratio. The gain adjusting
units 1401 to 140N adjust the gain of each acoustic signal based on the power ratio.
[0003]
Thanh Phong HUA, Akihiko SUGIYAMA, Gerard FAUCON, “A NEW SELF-CALIBRATION
TECHNIQUE FOR ADAPTIVE MICROPHONE ARRAYS”, IWAENC 2005 Proceedings, pp. 237240, [March 29, 2016 search], Internet <http: //
www.iwaenc.org/proceedings/2005/papers/S04-13.pdf>.
[0004]
In the level difference correction apparatus 900, there is a problem that an error occurs in the
correction of the level difference when the variation of the frequency characteristic is caused by
the mounting method of the microphone.
FIG. 10 shows the difference in characteristics depending on how the microphone is attached.
FIG. 10A is a view showing a state in which the microphone 40 is attached to the front surface
20 of the housing 10 and the microphone 50 is attached to the back surface 30. FIG. 10B is a
diagram showing the frequency characteristics when the front microphone and the rear
microphone collect the sound from the same sound source. In the low frequency region up to
several hundreds Hz, the same characteristics are shown regardless of the mounting position, but
in the high frequency region, it can be seen that the characteristics largely differ depending on
the mounting position.
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[0005]
The present invention has been made in view of such a situation, and it is an object of the present
invention to realize stable level difference correction even when variations in frequency
characteristics occur due to a method of attaching a microphone.
[0006]
The level difference correction device of the present invention performs level difference
correction of a plurality of acoustic signals collected by a plurality of microphones.
The level difference correction device of the present invention includes a low pass filter, a low
frequency time average power calculation unit, a power ratio calculation unit, and a gain
adjustment unit. The low pass filter passes only a predetermined low frequency signal for each
sound signal, and outputs a plurality of low frequency sound signals. The low frequency time
average power calculation unit obtains low frequency time average power which is time average
power for each low frequency acoustic signal. The power ratio calculation unit obtains, for each
of the low frequency time average powers, a ratio to the reference power obtained from the low
frequency time average power by a predetermined means, and uses it as the power ratio. The
gain adjustment unit adjusts the gain of each acoustic signal based on the power ratio.
[0007]
According to the level difference correction device of the present invention, the “predetermined
low frequency” can be set in a range where the difference in frequency characteristics due to
the mounting method of the microphone can be ignored. Therefore, even when variations in
frequency characteristics occur due to the mounting method of the microphone, stable level
difference correction can be realized because the gain is adjusted using a low frequency acoustic
signal having no variation in frequency characteristics.
[0008]
FIG. 2 is a view showing an example of the arrangement of a level difference correction
apparatus according to the first embodiment; FIG. 6 is a diagram showing an example of a
processing flow of the level difference correction device of the first embodiment. FIG. 7 is a view
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showing an example of the arrangement of a level difference correction apparatus according to
the second embodiment; FIG. 7 is a diagram showing an example of a processing flow of the level
difference correction device of the second embodiment. FIG. 7 is a view showing an example of
the arrangement of a level difference correction apparatus according to the third embodiment;
FIG. 14 is a diagram showing an example of the processing flow of the level difference correction
device of the third embodiment. FIG. 14 is a diagram showing an example of the configuration of
a level difference correction device according to a fourth embodiment. FIG. 18 is a diagram
showing an example of a process flow of the level difference correction device of the fourth
embodiment. FIG. 2 is a diagram showing the configuration of a level difference correction device
disclosed in Non-Patent Document 1. The figure which shows the difference in the characteristic
by how to attach a microphone.
[0009]
Hereinafter, embodiments of the present invention will be described in detail. Note that
components having the same function will be assigned the same reference numerals and
redundant description will be omitted.
[0010]
FIG. 1 shows a configuration example of the level difference correction device of the first
embodiment, and FIG. 2 shows an example of a processing flow of the level difference correction
device of the first embodiment. The level difference correction apparatus 100 performs level
difference correction of a plurality of acoustic signals collected by N microphones. However, N is
an integer of 2 or more. Also, n is an integer of 1 or more and N or less. The level difference
correction device 100 includes at least low pass filters 1101 to 110N, low frequency time
average power calculation units 1201 to 120N, power ratio calculation units 1302 to 130N, and
gain adjustment units 1402 to 140N. The number of power ratio calculators and gain adjusters
may be N-1 depending on the processing. However, a power ratio calculation unit 130 1, a gain
adjustment unit 140 1, and a reference power calculation unit 135 may also be provided. Details
will be described later. Further, for the description of the second embodiment and the following
embodiments, the entire configuration included in the level difference correction device 100 will
be referred to as a gain adjustment unit 150.
[0011]
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The low pass filters 110 1 to 110 N pass only predetermined low frequency signals for each
sound signal, and output N low frequency sound signals (S 110). For example, in the case of the
frequency characteristic shown in FIG. 10, if "predetermined low frequency" is set to 300 Hz or
less, only in the frequency region where there is no variation in frequency characteristic
depending on whether the microphone is attached front or back. The range in which there is no
variation in frequency characteristics varies depending on the actual microphone, the housing to
which the microphone is attached, and the like, and may be appropriately determined. In
addition, if the frequency range is low enough to contain almost no audio signal, even if there is a
level difference due to distance attenuation when speaking near the microphone, the audio signal
that is affected by distance attenuation is not included. Low frequency sound signal can be
output. The low frequency time average power calculation units 1201 to 120 N obtain low
frequency time average power which is time average power for each low frequency acoustic
signal (S120).
[0012]
The power ratio calculators 130 2 to 130 N determine the ratio to the reference power
calculated by the means determined in advance from the low frequency time average power, for
each low frequency time average power, and use it as the power ratio (S130). For example,
assuming that “reference power determined by a predetermined means” is the low frequency
time average power of the first channel, the power ratio of the first channel is 1, and the gain of
the acoustic signal of the first channel needs to be adjusted. Since there is not, the power ratio
calculation unit 130 1, the gain adjustment unit 140 1, and the reference power calculation unit
135 are unnecessary. The gain adjusting units 140 2 to 140 N adjust the gain of each acoustic
signal based on the power ratio (S 140).
[0013]
As described above, the power ratio calculation unit 130 1, the gain adjustment unit 140 1, and
the reference power calculation unit 135 may be provided. For example, "a reference power
determined by a predetermined means" may be an average of all the low frequency time average
powers determined by the reference power calculation unit 135. In this case, the power ratio
calculators 130 1 to 130 N calculate the ratio to the reference power calculated by the reference
power calculator 135 from the low frequency time average power for each low frequency time
average power as the power ratio (S130 ). The gain adjusting units 1401 to 140N adjust the gain
of each acoustic signal based on the power ratio (S140). The “reference power determined by a
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predetermined means” determined by the reference power calculation unit 135 does not have
to be limited to the average of all low frequency time average powers. For example, some
selected low frequency time average powers Or the n-th largest low frequency time average
power among all low frequency time average powers.
[0014]
According to the level difference correction device 100, the “predetermined low frequency”
can be defined in a range where the difference in frequency characteristics due to the mounting
method of the microphone can be ignored. Therefore, even when variations in frequency
characteristics occur due to the mounting method of the microphone, stable level difference
correction can be realized because the gain is adjusted using a low frequency acoustic signal
having no variation in frequency characteristics. In addition, if “predetermined low frequency”
is set in a range that hardly includes an audio signal, stable level difference correction can be
realized even when audio is input near the microphone and distance attenuation occurs between
the microphones.
[0015]
The structural example of the level difference correction apparatus of Example 2 is shown in FIG.
3, and the example of the processing flow of the level difference correction apparatus of Example
2 is shown in FIG. The level difference correction apparatus 200 includes a steady signal
detection unit 250 in addition to the gain adjustment unit 150. The gain adjustment means 150
is the same as the level difference correction device 100 of the first embodiment. The steady
signal detection unit 250 includes an acoustic time average power calculation unit 210, a noise
power estimation unit 220, a steady signal threshold setting unit 230, and a steady signal
threshold comparison unit 240.
[0016]
The sound time average power calculation unit 210 sets the time average power obtained based
on the sound signal as the sound time average power. The “time-averaged power determined
based on an acoustic signal” may be, for example, the time-averaged power of only the acoustic
signal of channel 1 or an average of the time-averaged power of all the acoustic signals. It may be
an average of time-averaged power of acoustic signals of several channels.
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[0017]
The noise power estimation unit 220 estimates noise power from the acoustic time average
power (S220). The noise power estimation unit 220 may perform dip-hold of the acoustic time
average power P (t) to estimate the noise power N (t). Here, t indicates discrete time. For
example, the following equation is used. N (t) = α · N (t−1) + (1−α) P (t) for N (t−1) <P (t) N (t)
= β · N (t−1) + ( 1−β) P (t) for N (t−1) ≧ P (t) where 0 ≦ β <α ≦ 1
[0018]
The stationary signal threshold setting unit sets a stationary signal threshold that is a threshold
based on noise power (S230). For example, the noise power N (t) estimated by the noise power
estimation unit 220 may be multiplied by a predetermined constant of one or more to obtain a
stationary signal threshold.
[0019]
The steady signal threshold comparison unit 240 compares the acoustic time average power with
the steady signal threshold and outputs a steady signal detection result (S240). In the level
difference correction device 200, the gain adjustment units 1401 to 140 N are based on the
acoustic signal when the steady signal detection result indicates that the acoustic time average
power is less than the steady signal threshold (when S240 is Yes). The gain for each acoustic
signal is adjusted (S150). Step S150 includes steps S110 to S140. However, the process not
necessarily performed when S240 is No is only step S140, and the conventional adjustment of
gain is maintained. Steps S110 to S130 may be processed in parallel with steps S210 to S240, or
only step S110 may be processed. For example, when only step S110 is processed in parallel,
whether or not the process of step S120 is to be performed is determined based on the result of
step S240. Then, when the process of S120 is not performed (when S240 is No), the low
frequency time average power calculation units 1201 to 120 N continuously output the low
frequency time average power at the time of the last processing. , Previous gain adjustments are
maintained. That is, the adjustment of the gain based on the acoustic signal when S240 is Yes is
maintained.
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[0020]
According to the level difference correction device 200, the steady signal detection means 250
detects a section with a small change in time, and adjusts the gain for each acoustic signal only in
the section. Therefore, a section including a signal with a large temporal change such as an audio
signal is not used for gain adjustment. That is, even when the “predetermined low frequency”
of the low-pass filters 110 1 to 110 N is determined in a range where the difference in frequency
characteristics due to the mounting method of the microphones can be ignored, the distance
between the microphones by approaching the microphones An effect is also obtained that
attenuation does not affect the gain adjustment. Therefore, stable level difference correction can
be realized.
[0021]
FIG. 5 shows an example of the configuration of the level difference correction apparatus of the
third embodiment, and FIG. 6 shows an example of the processing flow of the level difference
correction apparatus of the third embodiment. The level difference correction apparatus 300
includes a spectral shape similarity calculation unit 350 in addition to the gain adjustment unit
150. The gain adjustment means 150 is the same as the level difference correction device 100 of
the first embodiment. The spectral shape similarity calculation unit 350 includes frequency
conversion units 310 1 to 310 N, spectrum calculation units 320 1 to 320 N, a correlation
calculation unit 330, and a correlation threshold comparison unit 340.
[0022]
The frequency conversion units 310 1 to 310 N perform frequency conversion on each acoustic
signal and output a frequency acoustic signal (S310). For example, it may be converted to the
frequency domain by FFT (Fast Fourier Transform) or the like. The spectrum calculation units
320 1 to 320 N obtain a power spectrum for each frequency acoustic signal (S 320).
[0023]
The correlation calculation unit 330 obtains a cross correlation value between power spectra
(S330). The correlation threshold comparison unit 340 compares the cross correlation value with
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a predetermined correlation threshold and outputs a correlation result (S340). In the level
difference correction device 300, the gain adjustment units 1401 to 140 N are used for each
acoustic signal based on the acoustic signal when the correlation result indicates that the cross
correlation value exceeds the correlation threshold (when S340 is Yes). Adjust the gain of (S150).
Although step S150 includes steps S110 to S140, the process not necessarily performed when
S340 is No is only step S140, and the previous adjustment of gain is maintained. Steps S110 to
S130 may be processed in parallel with steps S310 to S340, or only step S110 may be processed.
For example, when only step S110 is processed in parallel, whether or not the process of step
S120 is to be performed is determined based on the result of step S340. Then, when the process
of S120 is not performed (when S340 is No), the low frequency time average power calculation
units 1201 to 120 N continuously output the low frequency time average power at the time of
the last processing. , Previous gain adjustments are maintained. That is, the adjustment of the
gain based on the acoustic signal when S340 is Yes is maintained.
[0024]
When the user breathes directly into the microphone when speaking, or when the wind hits the
microphone while using it outdoors, a large level of noise may be mixed between the
microphones without correlation. According to the level difference correction apparatus 300, the
gain adjustment is performed only when the spectral shapes of the sound signals are similar.
Therefore, an acoustic signal when a large level noise without correlation is mixed is not used for
gain adjustment. Therefore, stable level difference correction can be realized.
[0025]
A configuration example of the level difference correction device of the fourth embodiment is
shown in FIG. 7, and an example of a processing flow of the level difference correction device of
the fourth embodiment is shown in FIG. The level difference correction apparatus 400 includes,
in addition to the gain adjustment means 150, a steady signal detection means 250 and a
spectral shape similarity calculation means 350. The gain adjustment means 150 is the same as
the level difference correction device 100 of the first embodiment, the steady signal detection
means 250 is the same as the second embodiment, and the spectral shape similarity calculation
means 350 is the same as the third embodiment. The steady signal detection unit 250 includes
an acoustic time average power calculation unit 210, a noise power estimation unit 220, a steady
signal threshold setting unit 230, and a steady signal threshold comparison unit 240. The
spectral shape similarity calculation unit 350 includes frequency conversion units 310 1 to 310
N, spectrum calculation units 320 1 to 320 N, a correlation calculation unit 330, and a
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correlation threshold comparison unit 340. The processes (S110 to S140, S210 to S240, and
S310 to S340) of the respective configurations are the same as in the first to third embodiments,
and thus the description thereof will be omitted.
[0026]
Then, the level difference correction device 400 indicates that the steady signal detection result
indicates that the acoustic time average power is less than the steady signal threshold (S240 is
Yes), and that the cross correlation value exceeds the correlation threshold. Based on the acoustic
signal when the correlation result indicates (when S340 is Yes), the gain adjusting units 1401 to
140 N adjust the gain of each acoustic signal (S150). FIG. 8 shows a flow in which step S340 is
also executed when step S240 is YES, and the process proceeds to step S150 when step S340 is
YES. However, step S340 may be performed first, and in the case of Yes the process may proceed
to step S240.
[0027]
According to the level difference correction apparatus 400, all the effects shown in the first to
third embodiments can be obtained. In other words, when there is a difference in frequency
characteristics due to the mounting method of the microphones, when distance attenuation
occurs between the microphones by speaking close to the microphones, etc., even when a large
level of noise without correlation is mixed, Stable level difference correction can be realized.
[0028]
[Program, Recording Medium] The various processes described above are not only executed
chronologically according to the description, but also may be executed in parallel or individually
depending on the processing capability of the apparatus executing the process or the necessity. It
goes without saying that other modifications can be made as appropriate without departing from
the spirit of the present invention.
[0029]
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Further, when the above configuration is realized by a computer, the processing content of the
function that each device should have is described by a program. The above processing function
is realized on the computer by executing this program on the computer.
[0030]
The program describing the processing content can be recorded in a computer readable
recording medium. As the computer readable recording medium, any medium such as a magnetic
recording device, an optical disc, a magneto-optical recording medium, a semiconductor memory,
etc. may be used.
[0031]
Further, this program is distributed, for example, by selling, transferring, lending, etc. a portable
recording medium such as a DVD, a CD-ROM or the like in which the program is recorded.
Furthermore, this program may be stored in a storage device of a server computer, and the
program may be distributed by transferring the program from the server computer to another
computer via a network.
[0032]
For example, a computer that executes such a program first temporarily stores a program
recorded on a portable recording medium or a program transferred from a server computer in its
own storage device. Then, at the time of execution of the process, the computer reads the
program stored in its own recording medium and executes the process according to the read
program. Further, as another execution form of this program, the computer may read the
program directly from the portable recording medium and execute processing according to the
program, and further, the program is transferred from the server computer to this computer
Each time, processing according to the received program may be executed sequentially. In
addition, a configuration in which the above-described processing is executed by a so-called ASP
(Application Service Provider) type service that realizes processing functions only by executing
instructions and acquiring results from the server computer without transferring the program to
the computer It may be Note that the program in the present embodiment includes information
provided for processing by a computer that conforms to the program (such as data that is not a
direct command to the computer but has a property that defines the processing of the computer).
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[0033]
Further, in this embodiment, although the present apparatus is configured by executing a
predetermined program on a computer, at least a part of the processing contents may be realized
as hardware.
[0034]
100, 200, 300, 400, 900 Level difference correction device 110 Low pass filter 120 Low
frequency time average power calculation unit 130 Power ratio calculation unit 135 Reference
power calculation unit 140 Gain adjustment unit 150 Gain adjustment means 210 Acoustic time
average power calculation unit 220 Noise power estimation unit 230 stationary signal threshold
setting unit 240 stationary signal threshold comparison unit 250 stationary signal detection unit
310 frequency conversion unit 320 spectrum calculation unit 330 correlation calculation unit
340 correlation threshold comparison unit 350 spectral shape similarity calculation unit 920
time average power calculation Part 930 Power Ratio Calculator 935 Average Value Calculator
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