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DESCRIPTION JP2014187556

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DESCRIPTION JP2014187556
Abstract: [Problem] An object of the present invention is to provide a signal processing apparatus
capable of automatically reducing noise caused by blowing noise generated when inputting a
microphone or the like and noise outside in a simple configuration. SOLUTION: A signal
processing apparatus for reducing low frequency noise components from an input acoustic
signal, filter means for attenuating frequency components lower than a set cutoff frequency with
respect to the input acoustic signal, and a predetermined time Calculation means for acquiring
the spectrum of the input acoustic signal and calculating the average of the spectrum values for
each of a plurality of predetermined target frequencies, and the cutoff frequency obtained based
on the average of the spectrum values of the respective target frequencies And setting means for
setting the cutoff frequency of the filter means. [Selected figure] Figure 5
Signal processor
[0001]
The present invention relates to a technology for automatically reducing low-range spray noise
generated when a microphone or the like inputs a voice or the like, noise due to wind outdoors,
and the like.
[0002]
In a mixer, an audio interface or the like (hereinafter referred to as “device”), when a person's
voice is picked up using a voice input device, low frequency noise due to blowing of breath or the
like may be introduced.
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Also, when collecting sound with a microphone outdoors, low frequency noise may be introduced
due to the wind hitting the microphone.
[0003]
In order to suppress such noise, a simple method is to use a pop guard (a sponge-like cover
attached around a microphone) or the like to physically reduce the noise and the like by
spraying. There is also a method of providing a high pass filter (hereinafter referred to as "HPF")
on the processing path of the input signal on the device side and cutting low frequency noise as
needed. The cutoff frequency of the HPF has been manually set to, for example, 40 Hz, 60 Hz,. In
this case, the setting is often around 80 Hz or 100 Hz indoors, and the setting has been changed
according to the weather conditions (especially wind power) when outdoor.
[0004]
Patent Document 1 below includes a first microphone provided with shielding means for
shielding from the influence of external air flow and a second microphone not provided with
shielding means in order to acquire an audio signal with little wind noise. An audio signal of a
band lower than the resonance frequency of the shielding means is extracted from an audio
signal of the first microphone, and an audio signal of a band of a second frequency higher than
the frequency is extracted from an audio signal of the second microphone There is disclosed a
technique for acquiring a speech signal synthesized from them.
[0005]
JP, 2011-147103, A
[0006]
In the method using the pop guard described above, it is necessary to always prepare the pop
guard as a dedicated hardware, which is troublesome.
According to the method of cutting low frequency noise by HPF, pop guards and the like are not
necessary, but the cutoff frequency of HPF needs to be determined and set to an optimal value
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according to the situation.
Further, in the technique of Patent Document 1, two microphones are required, and the hardware
is complicated.
[0007]
An object of the present invention is to provide a signal processing apparatus capable of
automatically reducing, for example, noise caused by blowing noise generated when a voice or
the like is input to a microphone or wind outside in a simple configuration.
[0008]
In order to achieve the above object, the invention according to claim 1 is a signal processing
device for reducing a low frequency noise component from an input acoustic signal, which is
lower than a set cutoff frequency with respect to the input acoustic signal. Filter means for
attenuating frequency components, calculation means for acquiring the spectrum of an input
acoustic signal at predetermined time intervals, and calculating an average of spectrum values
for each of a plurality of predetermined target frequencies, and spectrum values of the respective
target frequencies And a setting unit configured to set a cutoff frequency obtained based on an
average of the above as the cutoff frequency of the filter unit.
[0009]
In the signal processing apparatus according to a second aspect of the present invention, in the
signal processing apparatus according to the first aspect, the setting means sets a difference
between the maximum value and the minimum value among the averages of the spectrum values
for each target frequency In the above case, the minimum value is set in the filter means as the
cutoff frequency.
[0010]
The invention according to claim 3 is the signal processing apparatus according to claim 1,
wherein the setting means does not have a minimum value smaller than a predetermined
minimum specified value among averages of spectrum values for each target frequency. And, in
the case where it is not larger than a predetermined maximum specified value, the minimum
value is set as the cut-off frequency in the filter means.
[0011]
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The invention according to claim 4 relates to the signal processing apparatus according to claim
1, wherein the setting means obtains a value serving as an index indicating the degree of
variation of the average of the spectrum values for each of the target frequencies, and the degree
of variation Is larger than a predetermined value, the minimum value is set as the cut-off
frequency in the filter means.
[0012]
According to the present invention, it is possible to automatically reduce, by a simple
configuration, spray noise generated when inputting a voice or the like into a microphone, noise
due to wind outdoors, and the like.
In particular, since low frequency noise can be reduced by using the HPF of the input channel
conventionally provided by a mixer or the like, dedicated hardware is not necessary, and it can be
realized only by preparing predetermined software. .
Also, since the HPF cutoff frequency is automatically set in real time, it is not necessary to worry
about the time change of the sound collection environment.
Also, in order to cut the low band, the region close to the fundamental frequency is cut.
Therefore, there is also an effect of howling prevention.
[0013]
Hardware configuration of mixer according to one embodiment of the present invention is a
block diagram showing a functional configuration of the mixer according to the embodiment
block diagram showing a schematic configuration of an input channel spectrum diagram of the
input signal spectrum frequency cutoff frequency setting and determination means Flow chart
showing another embodiment of the flow chart judging means
[0014]
Hereinafter, embodiments of the present invention will be described using the drawings.
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[0015]
FIG. 1 is a block diagram showing a hardware configuration of a mixer according to an
embodiment to which the signal processing apparatus of the present invention is applied.
A central processing unit (CPU) 101 is a processing unit that controls the overall operation of the
mixer.
The read only memory (ROM) 102 is a non-volatile memory storing various programs executed
by the CPU 101 and various data.
A random access memory (RAM) 103 is a volatile memory used for a load area or a work area of
a program executed by the CPU 101. The display unit 105 is a display for displaying various
information provided on the operation panel of the mixer. The operators 107 are various
operators provided on the operation panel for the user to operate. The communication I / O 109
is an input / output unit for connecting to various external devices. A display interface (IF) 104, a
detection IF 106, and a communication IF 108 are interfaces for connecting the display unit 105,
the operation element 107, and the communication I / O 109 to the communication bus 121,
respectively.
[0016]
A signal processing unit (DSP) 110 executes various microprograms based on an instruction of
the CPU 101 to perform various signal processing on the input digital sound signal, and outputs
the processed sound signal. An AD conversion unit 112, a DA conversion unit 113, and a digital
signal input / output unit (DD unit) 114 are connected to the DSP 110 via an audio bus 122. The
AD conversion unit 112 realizes a plurality of series of analog-to-digital conversion functions of
converting an analog audio signal input by a microphone or the like into a digital audio signal
and outputting the digital audio signal to the DSP 110 via the audio bus 122. The DA conversion
unit 113 realizes a plurality of series of digital analog conversion functions of converting digital
audio signals output from the DSP 110 into analog audio signals and outputting the analog audio
signals to audio devices such as amplifiers and speakers. The digital signal input / output unit
114 implements a plurality of digital input / output functions of inputting a digital signal from an
external device and passing it to the DSP 110 or outputting a digital audio signal output from the
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DSP 110 to an external device. EFX 111 is a signal processor (DSP) for performing an effect
giving process of the input digital sound signal.
[0017]
FIG. 2 is a block diagram showing a functional configuration of the mixer of the present
embodiment. A plurality of arrows entering the input patch 201 indicate a plurality of series of
input signals input by the AD conversion unit 112 or the DD unit 114 of FIG. 1. The input patch
201 patches (arbitrarily connects) input signals of these input ports to a plurality of input
channels 202. Each of the plurality of input channels 202 performs various signal processing on
the input signal based on the set parameters. The signals of these input channels 202 are sent
out to M MIX buses or Cue buses 203 (the bus configuration is optional), with the sending levels
set independently.
[0018]
Each of these buses 203 mixes the signals input from the input ch 202. The mixed signals are
output to the output ch 204 respectively. Each output ch 204 performs various signal processing
on the input signal based on the set parameters. The output of the output ch 204 is input to the
output patch 205. The output patch 205 patches (arbitrarily connects) signals output from the
output ch 204 to a plurality of output ports. A plurality of arrows extending from the output
patch 205 indicate a plurality of series of output signals output via the DA conversion unit 313
or the DD unit 314.
[0019]
The processing from the input patch 201 to the output patch 205 is mainly realized by the DSP
110 of FIG. 1 executing a predetermined microprogram. The micro program is sent from the CPU
101 to the DSP 110 for setting. The CPU 101 also sends to the DSP 110 and sets coefficient data
used when the DSP 110 executes the microprogram.
[0020]
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FIG. 3 is a functional block diagram showing a schematic configuration of one ch of the input ch
202 interposed between the input patch 209 and the bus 203. As shown in FIG. The attenuator
(Att) 301 and the head amplifier (H / A) 302 perform level control at the beginning of the input
signal. A high pass filter (HPF) 303 and an equalizer (EQ) 304 adjust frequency characteristics.
The gate (Gate) 305 is a noise gate that closes so that noise does not remain when the signal
level is lowered. The compressor (Comp) 306 performs automatic gain adjustment. The delay
(Delay) 307 is a delay circuit for performing phase alignment. A level (Level) 308 is a level
adjustment unit that adjusts the transmission level of the signal. Pan (Pan) 309 controls left and
right localization (pan) in the case of outputting a signal in stereo.
[0021]
In the mixer of this embodiment, the input signal input to the microphone is assigned to any of
the input channels 202 and subjected to signal processing as shown in FIG. In this case, the HPF
303 is conventionally provided to adjust the frequency characteristic, but in the present
embodiment, when the HPF (filter means) 303 is used to input voice or the like into a
microphone, Reduce low frequency noise such as generated spray noise and wind noise outdoors.
The user can designate enabling / disabling of the low frequency noise reduction function for any
input channel. In the input channel in which the function is effectively set, the cutoff frequency of
the HPF 303 is automatically set according to the principle and operation described below to
reduce the above-mentioned low frequency noise.
[0022]
FIG. 4 is a spectrum diagram for explaining the principle of how to determine the cutoff
frequency of the HPF 303. The horizontal axis shows the frequency of the input signal, and the
vertical axis shows the signal strength for each frequency. The dotted line graph 401 shows the
current value of the spectrum obtained by FFT (Fast Fourier Transform) processing at a certain
point in time of the input signal of the human voice input by microphone. In the present
embodiment, the current value of the spectrum of the input signal is acquired at predetermined
time intervals. To that end, the mixer of this embodiment is provided with analysis software
including an FFT, and operates the software with the DSP 110 to acquire the current value of the
spectrum of the input signal of the designated input channel.
[0023]
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From the current value of the spectrum of the input signal acquired at each predetermined time,
spectral values of predetermined several frequencies are acquired and held for each time. Here, it
is assumed that the spectral values of the target frequencies of 40 Hz, 60 Hz, 80 Hz, 100 Hz, and
120 Hz are retained, and the latest n values (n is an integer of 2 or more) Obtain and hold the
spectrum value of For example, S1 to Sn indicated by numbering 403 on the 100 Hz axis in FIG.
4 are the spectrum values at which Sn was acquired most recently, the spectrum values at which
Sn-1 was acquired one time ago,. S1 shows the spectrum value acquired n-1 times ago.
[0024]
Next, the average (S1 + S2 +... + Sn) / n of the n spectral values is determined for each of the
target frequencies described above. The white circles in FIG. 4 (for example, the white circles
404) indicate the average of the latest n spectrum values of each target frequency. Reference
numeral 402 indicates the maximum value (history) of the n spectra obtained at each
predetermined time. Here, it is assumed that the point where the spectral average value is higher
(40 Hz or 120 Hz in FIG. 4) indicated by a white circle is that the frequency is either noise or a
voice component. On the other hand, it can be determined that the point (80 Hz in FIG. 4) with
the lowest spectral average value indicated by the white circle is the boundary point between the
noise part and the basic part of the voice. Therefore, the frequency at which the spectrum
average value is minimum is set as the cutoff frequency of the HPF 303. As described above, for
low frequency noise caused by spraying, etc., the frequency of the spectral point with the lowest
relative level is considered to be the boundary between noise and voice, so set that frequency in
the HPF 303 as the optimal cutoff frequency. This can reduce low frequency noise.
[0025]
Although FIG. 4 exemplifies a case in which the average value of n times of white circles is the
minimum value at an intermediate position (80 Hz) of the above target frequencies, for example,
the average value takes the minimum value at the minimum frequency 40 Hz. In the case where
the frequency increases to the upper right as the frequency increases, the frequency 40 Hz at
which the average value becomes the minimum value is set as the cutoff frequency of the HPF
303. In this case, in fact, there is a possibility that the cutoff frequency should be larger, but the
setting is made in consideration of safety without reducing the audio part. The default value may
be set as the minimum frequency (for example, 20 Hz or 40 Hz), and the minimum frequency
may be set as the cutoff of the HPF first, and then it may be reset when the measurement
proceeds and an appropriate value is obtained. . In addition, when the noise floor is extremely
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high (for example, when the surrounding noise is very large) due to the recording environment
etc., it becomes difficult to distinguish the spraying noise from the noise other than that, and the
above n times of averages There is a possibility that the frequency position where the value
becomes the minimum may vary, in which case the HPF may not be applied or the above default
value may be used as it is.
[0026]
As the calculation result of the spectrum average value at each of the target frequencies
described above, the larger the value of n, the more accurate the determination can be made, but
at the same time the calculation load becomes larger. Practically, for example, in the case of
music, it is assumed that n = 100 spectrum values are acquired within a time (about 15 seconds,
for example) of one chorus phrase. Also, if the user has disabled the HPF setting, that will be
prioritized and disabled. If the user has enabled HPF settings and the measurement is complete,
the optimal value is selected. In the measurement incomplete state, it is assumed that a default
value is selected.
[0027]
Once the cutoff frequency of the HPF is set according to the above principle, the cutoff frequency
does not have to be changed, but the cutoff frequency may be set again if various environments
change. In addition, when the environment changes in real time, the cutoff frequency may be set
again at predetermined time intervals.
[0028]
FIG. 5A is a setting flow of the cut-off frequency in the mixer of this embodiment. This process is
executed for an input channel designated to reduce low frequency noise by the user, and in
particular, processing for acquiring spectrum values at predetermined time intervals for an input
signal input to the input channel is performed. It is assumed that the latest n spectral values of
each target frequency have been acquired at least n times.
[0029]
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In step 501, an average value of spectrum values for the past n times is determined for each
target frequency. The target frequency is, for example, 40 Hz, 60 Hz, 80 Hz, 100 Hz, and 120 Hz
as described above, and is selected in advance. Here, m frequencies of f1, f2, ..., fm are used. The
calculation formula of the average value may be calculated, for example, as Ave (f1) = (S1 + S2 +...
+ Sn) / n for f1. Step 501 corresponds to calculation means for calculating an average of
spectrum values. Next, in steps 502 and 503, the minimum value min (Ave (f1), Ave (f2), ..., Ave
(fm)) and the maximum value max (Ave (f1) of the average value of the spectrum of each of m
target frequencies. , Ave (f2), ..., Ave (fm)) are calculated. At step 504, the cutoff frequency of the
HPF 303 is determined and set by the determination means. Step 504 corresponds to setting
means of the cutoff frequency.
[0030]
FIG. 5 (b) shows the procedure of the determination means of step 504. In step 511, it is
determined whether the difference obtained by subtracting the minimum value obtained in step
502 from the maximum value obtained in step 503 is smaller than a specified value. The
prescribed value is a predetermined value. If “maximum value−minimum value <prescribed
value”, it is determined that there is no difference that can be regarded as significant between
the maximum value and the minimum value, and in step 512, the default frequency (for example,
20 Hz or 40 Hz) Set as the cutoff frequency of the HPF 303. If not “maximum value−minimum
value <prescribed value”, it is determined that the position of the minimum value is the
boundary between voice and low frequency noise, and in step 513, the frequency of the
minimum value is set as the cutoff frequency of the HPF 303.
[0031]
FIG. 6 (a) shows another example of the determination means of step 504. FIG. At step 601, the
value of the minimum value obtained at step 502 is determined. If "minimum value <minimum
specification value" or "maximum specification value <minimum value" with respect to
predetermined minimum specification value and maximum specification value, the minimum
value is "too small" or "too large", so the voice And the low frequency noise, and can not be
viewed as a significant boundary, and in step 602, the default frequency is set as the cutoff
frequency of the HPF 303. If “minimum specification value <= minimum value <= maximum
specification value”, it is determined that the minimum value can be regarded as a significant
boundary between voice and low frequency noise, and in step 603, the frequency of the
minimum value Is set as the cutoff frequency of the HPF 303.
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[0032]
FIG. 6B shows still another example of the determination means of step 504. In step 611, the
variance var (Ave (f1), Ave (f2), ..., Ave (fm)) of the average value of the spectrum of the target
frequency is calculated. In step 612, it is determined whether or not “variance value
<prescribed value”. This prescribed value is a predetermined value. If “dispersion value
<prescribed value”, it means that the average value of the spectrum of the target frequency is
not dispersed so much, and it is determined that the minimum value can not be regarded as a
significant boundary between voice and low frequency noise. Then, in step 613, the default
frequency is set as the cutoff frequency of the HPF 303. If “dispersion value <prescribed
value” is not satisfied, it is determined that the average value of the spectrum of the target
frequency is dispersed to some extent, and the minimum value can be regarded as a significant
boundary between voice and low frequency noise. The frequency of the minimum value is set as
the cutoff frequency of the HPF 303. A standard deviation or the like may be used instead of the
variance.
[0033]
101: central processing unit (CPU) 102: read only memory (ROM) 103: random access memory
(RAM) 105: display unit 107: operator 109: communication I / O 110: signal processing unit
DSP) 112 AD conversion unit 113 DA conversion unit 114 digital signal input / output unit (DD
unit) 303 HPF 401 current value of spectrum 404 average value of n times.
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