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DESCRIPTION JP2004080464

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DESCRIPTION JP2004080464
An automatic wind noise reduction circuit and an automatic wind noise reduction method
capable of improving the performance and freedom of system design in response to multichanneling of audio signals. SOLUTION: An addition signal of audio signals for audio channels
other than the audio channel selected to be different from one another is obtained by the
operators 26, 27, 28, and the audio selected by the operators 29, 30, 31 is obtained. The
addition signal from the corresponding computing unit 26, 27, 28 is subtracted from the audio
signal of the channel. The subtraction signals from the arithmetic units 29, 30, 31 are bandlimited to the frequency band of the wind noise signal by the LPFs 21, 23, 25, and the
subtraction signals from the band-limited arithmetic units 29, 30, 31 are leveled. After level
control by the variable amplifiers 32, 33, 34, they are subtracted from the audio signal of the
corresponding audio channel. [Selected figure] Figure 1
Automatic wind noise reduction circuit and automatic wind noise reduction method
The present invention relates to an automatic wind noise reduction circuit for reducing wind
noise of an audio signal to be processed and an automatic wind noise reduction, for example, in
an apparatus for processing an audio signal such as a digital video camera. On the way. 2.
Description of the Related Art In a camera-integrated VTR such as a digital video camera, sound
is collected using a plurality of built-in microphones disposed at an arbitrary interval, and L is
transmitted through a directivity operation circuit. It is generally recorded on a recording
medium as a stereo audio signal of two channels (left channel) and R (right channel).
Furthermore, in outdoor photography using a camera integrated type VTR, in most cases, wind
noise due to wind noise is collected together with an audio signal, and it has been extremely
unpleasant in the past. However, in Japanese Patent Application Laid-Open Nos. 11-69480 and
2001-186585, only the wind sound signal is used as a circuit in the mixed signal of the sound
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signal collected through the microphone and the wind sound signal. A wind noise reduction
circuit that automatically reduces noise has been proposed, and a method for reducing offensive
wind noise has been provided. By the way, in the method disclosed in the above-mentioned
Japanese Patent Laid-Open Publication No. 11-69480 Patent Publication and Japanese Patent
Laid-Open Publication No. 2001-186585 Patent Publication, the audio signal is composed of L
and R. Because the wind noise reduction circuit is configured on the premise that it is recorded
as a two-channel stereo audio signal, it is not possible to cope with the recording of audio signals
of three or more channels. That is, even when three or more microphone capsules (microphones)
are used, wind noise reduction processing is always performed as audio signals of two channels
via a directivity calculation circuit such as stereo sound field processing. Therefore, in the
conventional wind noise reduction circuit, the restriction operation of inserting in the latter stage
of the directivity operation circuit such as the above-mentioned stereo sound field processing
occurs in most cases, and the directivity operation circuit of performance improvement and
system design freedom improvement. It was not possible to enjoy the merit of inserting the wind
noise reduction circuit in the previous stage of. Further, looking at the recording format of the
current consumer DV (digital video), multi-channel recording up to 4 channels is possible, and
the recent MPEG / AAC (Advanced Audio Coding) method, Dolby Digital method, DTS It is
expected in the future to provide a camera integrated type VTR that adopts multi-channel
recording such as the Digital Theater System method, and it is desired to provide an automatic
wind noise reduction circuit corresponding to multi-channel recording of audio signals. .
In view of the above, the present invention is an automatic wind noise reduction that can
eliminate the above-mentioned problems, respond to multi-channeling of audio signals, and
improve performance and system design freedom. It is an object to provide a circuit and an
automatic wind noise reduction method. SUMMARY OF THE INVENTION In order to solve the
above problems, the automatic wind noise reduction circuit of the invention according to claim 1
comprises N (N is a positive number of 2 or more) audio channels, and First addition means for
adding all audio signals of N-1 audio channels other than one audio channel selected from the N
audio channels, and the selection not added in the first addition means First subtracting means
for subtracting the addition signal from the first adding means from the audio signal of one audio
channel to be selected; N in the previous stage of the first adding means and the first subtracting
means A first component for extracting a band component of a wind sound signal for an output
signal from the first subtraction means, for each of audio signals of a number of audio channels
or in a stage subsequent to the first subtraction means. Output means, first gain control means
for controlling the gain of the output signal from the first subtraction means band-limited by the
first extraction means, and an audio signal of the selected one audio channel And second
subtracting means for subtracting a signal whose gain is controlled by the first gain control
means; and an output signal of the second subtracting means as an audio output of the selected
one audio channel It is characterized by According to the automatic wind noise reduction circuit
of the first aspect of the present invention, the first addition means obtains an addition signal of
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audio signals for audio channels other than the audio channel selected in advance. The addition
signal from the first addition means is subtracted from the audio signal of the selected audio
channel by the 1 subtraction means to obtain a subtraction signal. The subtraction signal is a
signal of a band component of the wind noise signal at a stage before the first addition means
and the first subtraction means, or at a stage after the first subtraction means. The bandwidth is
limited by the extraction means of The gain of the subtraction signal from the first subtraction
means adapted to band-limit is controlled by the first gain restriction means, and the gaincontrolled subtraction signal is an audio signal of the selected audio channel (band-limited And
the sound signal after subtraction is used as the output signal of the selected audio channel.
Thus, only the wind sound signal is canceled from the sound signal of the selected sound channel
including the wind sound signal, and the sound signal in which the wind sound signal is
effectively reduced can be obtained. . Further, by providing the automatic wind noise reduction
circuit having the above-described configuration in a target audio channel among audio channels
having a plurality of channels, the wind noise signal can be effectively reduced from the audio
signal of the audio channel. . The automatic wind noise reduction circuit of the invention
according to claim 2 is the automatic wind noise reduction circuit according to claim 1,
comprising: the first addition means; and the first subtraction means The first extraction unit, the
first gain control unit, and the second subtraction unit corresponding to the N audio channels for
N channels, and the selected one audio channel Are characterized in that they do not overlap in
each system. According to the automatic wind noise reduction circuit of the second aspect of the
present invention, the automatic wind noise reduction circuit is provided for each of the N audio
channels, and It is made possible to reduce wind noise from each audio signal. That is, since the
sound signal for each sound channel can be processed to reduce the wind sound signal, it is
possible to cope with not only two stereo channels but also multi-channels of three or more
channels. Be done. [0015] The automatic wind noise reduction circuit of the invention according
to claim 3 is the automatic wind noise reduction circuit according to claim 1 or 2, wherein the
audio signals of the N audio channels are included. Third subtraction means for obtaining a
difference voice signal between arbitrary voice signals; second extraction means for extracting a
band component of a wind sound signal from the difference voice signal from the third
subtraction means; A detection unit which is supplied with an extraction signal from the
extraction unit 2 and generates a level detection signal of the wind sound signal; and, based on
the level detection signal from the detection unit, the first gain control unit It is characterized in
that the gain is variably controlled. According to the automatic wind noise reduction circuit
according to the third aspect of the present invention, it is possible to calculate the difference
between the voice signals of arbitrary voice signals among the voice signals of N voice channels
according to the level of the actual wind noise signal. A level detection signal is obtained, and
based on the level detection signal, the gain in the first gain control means is controlled.
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Thus, the level of the subtraction signal from the first subtraction circuit for canceling the wind
sound signal can be controlled in accordance with the actual level of the wind sound signal
included in the sound signal. The wind noise signal included in the signal can be effectively
canceled corresponding to the level. The automatic wind noise reduction circuit of the invention
according to claim 4 is the automatic wind noise reduction circuit according to claim 2 or claim
3, wherein the second subtraction means for the N systems A second adding means for adding all
output signals from each of the above, a third extracting means for receiving a signal from the
second adding means and extracting a band component of a wind sound signal, the third A
second gain control means for controlling the gain of the output signal from the extraction
means; and an output signal of the second gain control means from an output signal from each of
the N subtractions of the N systems. And the fourth subtraction means for N series to be
subtracted, and the output signal from each of the Nth series of fourth subtraction means is used
as the audio output of the N audio channels. . According to the automatic wind noise reduction
circuit of the fourth aspect of the invention, the output signals from the N second subtraction
means are added by the second addition means, and the second extraction means , And the gain
is controlled by the second gain control means. This gain-controlled signal is subtracted from
each of the output signals of the N second subtraction means in the fourth subtraction means,
corresponding to the N audio channels in which the residual component of the wind sound signal
is also canceled. N audio signals are obtained. [0020] Thus, the wind sound signal component
remaining in the sound signal in which the wind sound signal is reduced can be further
effectively reduced, and the sound signal in which the wind sound signal is not noticeable can be
output. The automatic wind noise reduction circuit of the invention according to claim 5 is the
automatic wind noise reduction circuit according to claim 4, wherein the second gain is detected
by the level detection signal from the detection means. An automatic wind noise reduction circuit
characterized by variably controlling a gain of a control means. According to the automatic wind
noise reduction circuit of the fifth aspect of the present invention, in the second gain limiting
means, the gain of the input signal is controlled based on the level detection signal from the
detection means. Be done. Thus, the level of the signal used to cancel the wind sound signal can
be controlled according to the level of the actual wind sound signal included in the audio signal,
so that the wind sound signal remaining in the audio signal can be Being able to cancel
effectively.
BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an automatic wind noise
reduction circuit and an automatic wind noise reduction method according to the present
invention will be described below with reference to the drawings. First, in order to simplify the
entire description, the frequency characteristics of the wind sound signal in a general video
camera (camera integrated VTR) and an example of a conventional L / R 2-channel wind sound
reduction circuit will be described. [Regarding Frequency Characteristics of Wind Sound Signal]
FIG. 4 is a diagram showing an example of frequency characteristics of a wind sound signal
collected by a general video camera. As shown in FIG. 4, the wind sound signal increases in level
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at 1 / F characteristics (F is frequency) as the frequency decreases from about 1 kHz. However,
due to the characteristics of the microphone unit used and the coupling capacitor of the analog
circuit that processes the audio signal, the level decreases at extremely low frequencies, so it has
a peak around about 200 Hz. In addition, since the wind sound signal is caused by the vortex-like
air flow generated in the vicinity of the microphones, the wind sound signals from the respective
microphones are random signals which are not correlated with the sound signal. [Regarding TwoChannel Wind Noise Reduction Circuit] Next, a conventional L / R two-channel wind noise
reduction circuit for reducing a wind noise signal having the characteristics as described above
will be described. FIG. 5 is a block diagram for explaining a conventional L / R 2 channel wind
noise reduction circuit. Audio signals of Rch (right channel) and Lch (left channel) including wind
noise signals collected by the microphones 101 and 102 are converted to ADC (Analog to Digital
Converter) 105 via the amplifiers 103 and 104, respectively. , 106, where it is analog-to-digital
converted into a digital signal. The Rch-side audio signal converted to a digital signal in the ADC
105 is supplied to the delay unit 107 and the − (minus) terminal of the computing unit 109, and
the Lch-side audio signal converted to a digital signal in the ADC 106 is The delay unit 108 and
the plus (+) terminal of the computing unit 109 are supplied. The computing unit 109 computes
a difference component (LR) signal between the Rch side audio signal and the Lch side audio
signal, and supplies this to LPF (Low-Pass Filter) 110 and 121. Here, as described above, since
the wind sound signal has no correlation between the L / R channels, the difference component
(L-R) signal passes only the wind sound band shown in FIG. 4 in the LPF 110. By doing this, most
wind noise signals can be extracted.
Further, in the LPF 121, when the extremely low frequency is further passed, it is possible to
extract only the wind sound signal which hardly includes the audio signal. Then, the output from
the LPF 121 is amplified by the amplifier 122, and the wind noise signal is level detected by the
DET (detection processing unit) 123. The level detection output from the DET 123 is supplied to
the coefficient generation unit 124. The coefficient generation unit 124 shapes the level
detection output from the DET 123 to generate a wind sound level detection signal as a control
coefficient to the next stage, and supplies this to the level variable amplifiers 111 and 118.
Further, the output from the above-described LPF 110 is level controlled in the level variable
amplifier 111 by the wind sound level detection signal from the coefficient generation unit 124.
At this time, the level variable amplifier 111 is controlled so that the output is large when the
wind noise is large, that is, the level of the wind noise level detection signal is large. Conversely,
when there is no wind noise, the level of the wind noise level detection signal Is controlled to be
zero and the output to be zero. Then, as shown in FIG. 5, the output signal from the level variable
amplifier 111 is added to the delayed signal from the delay unit 107 in the operation unit 112,
and the delay from the delay unit 108 is performed in the operation unit 113. Is subtracted from
the received signal. The meaning of the operations in these computing units 112 and 113 will be
described. First, let the Lch audio signal be Ls, the Lch wind sound signal be Lw, the Rch audio
signal be Rs, the Rch wind sound signal be Rw, and when the wind sound is at a maximum, the
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output / input ratio of the level variable amplifier 111 Is set to 0.5 times, the output Ra of the
computing unit 112 and the output La of the computing unit 113 are expressed by the equations
(1) and (2), respectively. Ra = (Rs + Rw) + 0.5 (Lw-Rw) = Rs + 0.5 (Lw + Rw) (1) Formula La = (Ls +
Lw)-0.5 (Lw-Rw) = Ls + 0.5 (Lw + Rw) ) (2). That is, when the wind sound signals Rw and Lw are
large, both the wind sound signals are monaural signals with the (Lw + Rw) component, and
when the wind sound signals Rw and Lw are zero, the respective audio signals Rs and Ls are
output. Ru. The wind noise signal can be greatly reduced by the addition because there is no
correlation between the channels compared to the audio signal. Further, the delay units 107 and
108 compensate for the delay due to the LPF 110 on the main line side, and the signal timing in
the arithmetic units 112 and 113 is matched to further improve the reduction effect.
Further, the outputs of the computing units 112 and 113 are input to the delay units 115 and
116, respectively, and are also input to the computing unit 114 to be added to each other, and
the output is supplied to the LPF 117. The LPF 117 is set to a band for extracting a wind noise
band, as in the LPF 110. The output of the LPF 117 is level controlled in the level variable
amplifier 118 by the wind noise level detection signal from the coefficient generation unit 123
described above, and the output is high when the wind noise is large, that is, the wind noise level
detection signal is large. It is controlled to be large, and conversely, when there is no wind noise,
the level of the wind sound level detection signal is controlled to be zero and the output to be
zero. The output of the level variable amplifier 118 is subtracted from the signal passed through
the delay unit 115 in the computing unit 119 and is subtracted from the signal passed through
the delaying unit 116 in the computing unit 120. The meaning of the operations in these
computing units 119 and 120 will be described. First, using the equations (1) and (2) described
above and setting the output / input ratio of the level variable amplifier 118 to 0.5 when the
wind noise is maximum, the output Rb of the operator 119 and the operator The outputs Lb of
120 are respectively expressed by equations (3) and (4). Rb = Rs + 0.5 (Lw + Rw) -0.5 (Lw + Rw) =
Rs (3) Formula Lb = Ls + 0.5 (Lw + Rw) -0.5 (Lw + Rw) = Ls (4) formula. Therefore, the wind
sound signals Rw and Lw are canceled to obtain only the audio signals Rs and Ls. Further, the
delay units 115 and 116 described above compensate the delay due to the LPF 117 on the main
line side, and the signal timing of the arithmetic units 119 and 120 is matched to further
improve the reduction effect. Therefore, the output signals of the computing units 119 and 120
become audio signals with reduced wind and sound signals as described above, and are input to
recording system signal processing in the case of a video camera, and are output together with
video signals from the video signal system. It will be recorded on a recording medium. [About
Multi-Channel Automatic Wind Noise Reduction Circuit and Automatic Wind Noise Reduction
Method] As described above, in the case of the conventional L / R 2 channel wind noise reduction
circuit, an effect is achieved according to the level of the wind noise signal. Although it is possible
to reduce wind noise, if the sound channel is assumed to be L / R2 channel, the wind sound must
be changed to two even if the sound channel is a multi channel with three or more channels. The
reduction processing can not be performed, and the degree of freedom in performance and
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system design can not be improved.
In the automatic wind noise reduction circuit and the automatic wind noise reduction method
according to the present invention described below, even in the case of a multichannel of three
or more channels, each signal is not converted into L / R2 channel audio signals. It is possible to
effectively reduce only the wind sound signal from the synthesized signal composed of the sound
signal of the channel and the wind sound signal. In the following, the case of three audio signal
channels will be described as an example. FIG. 1 is a block diagram for explaining an automatic
wind noise reduction circuit 1 to which an automatic wind noise reduction circuit corresponding
to a multi-channel according to the present invention and an automatic wind noise reduction
method are applied. As shown in FIG. 1, the automatic wind noise reduction circuit 1 of this
embodiment is capable of processing three audio signals picked up by the three microphones 10,
11, 12 independently. It is a thing. The audio signal of Rch (right channel) collected by the
microphone 11, the audio signal of Cch (center channel) collected by the microphone 10, and the
Lch (left channel) collected by the microphone 12 Each audio signal is supplied to the
corresponding ADC 16, 17, 18 through the corresponding amplifier 13, 14, 15. Each of the ADCs
16, 17, 18 converts the analog audio signal from each of the corresponding amplifier 13, 14, 15
into a digital signal. The Rch digital audio signal R from the ADC 16 is supplied to the delay unit
20, the LPF 21 and the negative terminal of the computing unit 19, and the Cch digital audio
signal C from the ADC 17 is connected to the delay unit 22. The Lch digital audio signal L
supplied from the ADC 18 is supplied to the delay unit 24, the LPF 25, and the positive terminal
of the computing unit 19. Arithmetic unit 19 subtracts the digital audio signal R of Rch supplied
to the negative side terminal from the digital audio signal L of Lch supplied to the positive side
terminal, and outputs the result as the output signal (LR) The signal is supplied to the LPF 121,
and the wind noise level detection signal is generated through the amplifier 122, the DET 123,
and the coefficient generation unit 124. The method of generating the wind noise level detection
signal is the same as that of the two channel wind noise reduction circuit shown in FIG. Further,
the Rch digital audio signal (wind noise signal of Rch) Rw limited to the wind noise band shown
in FIG. 4 in the LPF 21 is the + side terminal of the computing device 30 and one plus of the
computing device 26. The Cch digital audio signal (Cch wind sound signal) Cw, which is supplied
to the side terminal and one positive side terminal of the calculator 27 and limited to the wind
sound band shown in FIG. The Lch digital audio signal (Lch) supplied to the + side terminal, the
other + side terminal of the computing unit 26, and one + side terminal of the computing unit 28
and limited to the wind and sound band shown in FIG. The wind sound signal Lw is input to the +
side terminal of the computing unit 29, the other + side terminal of the computing unit 28, and
the other + side terminal of the computing unit 27.
Further, the (Rw + Cw) signal which is an addition signal of the Rch wind sound signal Rw from
the arithmetic unit 26 and the wind sound signal Cw of Cch is supplied to the negative side
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terminal of the arithmetic unit 29. It is subtracted from the wind noise signal Lw of Lch supplied
to the + side terminal, and is supplied to the level variable amplifier 34 as a (Lw-Rw-Cw) signal.
Similarly, the (Rw + Lw) signal which is the addition signal of the Rch wind sound signal Rw from
the arithmetic unit 27 and the Lch wind sound signal Lw is input to the negative side terminal of
the arithmetic unit 31, and the arithmetic unit 31 It is subtracted from the wind noise signal Cw
of Cch supplied to the + side terminal of the Vch and supplied to the level variable amplifier 33
as a (Cw-Rw-Lw) signal. Further, the (Lw + Cw) signal which is the addition signal of the Lch wind
sound signal Lw from the arithmetic unit 28 and the wind sound signal Cw of the Cch is input to
the negative side terminal of the arithmetic unit 30. It is subtracted from the wind noise signal
Rw of Rch supplied to the + side terminal, and is supplied to the level variable amplifier 32 as a
(Rw-Lw-Cw) signal. Each of the level variable amplifiers 32, 33, 34 is level controlled by the
above-described wind noise level detection signal from the coefficient generation unit 124, and
the wind noise is large, that is, the wind noise level detection signal has a large level. When the
wind noise level is not controlled, the level of the wind noise level detection signal is controlled to
be zero and the power is controlled to be zero. Furthermore, the output signals from the level
variable amplifiers 32, 33, 34 are input to the negative terminals of the computing units 35, 36,
37, respectively, and the positive terminals from the corresponding delay units 20, 22, 24
respectively. Is subtracted from each of the digital audio signals R, C, and L supplied to the
circuit, and the output signal is output as an Rch signal, a Cch signal, and an Lch signal from the
corresponding terminals 40, 41, 42, and a wind sound level detection signal Is output from the
terminal 43 as a detection output. The operation of the automatic wind noise reduction circuit 1
of this embodiment shown in FIG. 1 will now be described. Here, the Lch audio signal is Ls, the
wind sound signal is Lw, the Rch audio signal is Rs, the wind sound signal is Rw, the Cch audio
signal is Cs, the wind sound signal is Cw, and the wind sound is maximum. Set the output / input
ratio of the level variable amplifiers 32, 33, 34 to 0.5, and output signals of Rch signal, Cch
signal, Lch signal output from the output terminals 40, 41, 42. Assuming that each is represented
by Ra, Ca, and La, each of them is represented by the following formulas (5), (6), and (7).
Ra = (Rs + Rw)-0.5 (Rw-Lw-Cw) = Rs + 0.5 (Rw + Lw + Cw) (5) Formula Ca = (Cs + Cw)-0.5 (Cw-RwLw) = Cs + 0.5 (Rw + Lw + Cw) (6) Formula La = (Ls + Lw)-0.5 (Lw-Rw-Cw) = Ls + 0.5 (Rw + Lw +
Cw) (7) Formula. That is, when the wind noise is large, any wind noise signal in each output is a
(Rw + Lw + Cw) component, which is a monaural signal obtained by adding the wind noise
signals of all the channels. Wind sound signals having no correlation between channels can be
greatly reduced by adding them. Also, when there is no wind noise, Rw, Cw, and Lw become zero,
and the respective audio signals Rs, Cs, and Ls are output. Further, the delay units 20, 22 and 24
respectively compensate the delay due to the LPFs 21, 23 and 25 on the main line side, and the
signal timings in the arithmetic units 35, 36 and 37 are matched, It is reducing the effect.
Further, the LPFs 21, 23, 25 can extract most of the wind sound signals by using the wind sound
band shown in FIG. 4 as a pass band, and the LPF 121 can transmit only extremely low frequency
signals, and only wind sound signals hardly include audio signals. Is extracted. Although the
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(L−R) signal is used by the computing unit 19 to generate the wind and sound level detection
signal in FIG. 1, the present invention is not limited to this. A (CR) signal or an (LC) signal may be
used, and the maximum value may be selected from among the combination of these difference
components. As described above, the automatic wind noise reduction circuit shown in FIG. 1 is
provided with an automatic wind noise reduction circuit for each audio channel. That is, as also
shown in FIG. 1, for Rch, an arithmetic unit 28 (first addition means), an arithmetic unit 30 (first
subtraction means), a level variable amplifier 32 (first gain control means) , An automatic wind
noise reduction circuit including an arithmetic unit 35 (second subtraction means), and for Cch,
an arithmetic unit 27 (first addition means), an arithmetic unit 31 (first subtraction means), An
automatic wind noise reduction circuit including a level variable amplifier 33 (first gain control
means) and an arithmetic unit 36 (second subtraction means) is provided. Further, for Lch,
arithmetic unit 26 (first addition means), arithmetic unit 29 (first subtraction means), level
variable amplifier 34 (first gain control means), arithmetic unit 37 ( The automatic wind noise
reduction circuit comprising the second subtraction means is provided.
Further, each of the LPFs 21, 23, 25 corresponds to a first extracting unit. Thus, by providing an
automatic wind noise reduction circuit for each audio channel, the wind noise signal is reduced
for the audio of each audio channel, regardless of the number of audio channels. I am able to do
that. The present invention is not limited to the case where an automatic wind noise reduction
circuit is provided for each of a plurality of audio channels. For example, an automatic wind noise
reduction circuit may be provided only for Lch (left channel) and Rch (right channel). An
automatic wind noise reduction circuit may be provided for the selected audio channel. As
described above, by providing the automatic wind noise reduction circuit only in the voice
channel where it is easy to pick up the wind noise signal, it is possible to construct an
inexpensive voice signal processing system in which the wind noise signal is reduced. Be able to
do it. However, in the case of the automatic wind noise reduction circuit 1 shown in FIG. 1, the
wind noise signal remains, as can be understood from the above-mentioned equations (5), (6) and
(7). Therefore, by providing an automatic wind noise reduction circuit for residual wind noise
reduction at the subsequent stage of the automatic wind noise reduction circuit 1 shown in FIG.
1, it is possible to further reduce the remaining wind noise signal. FIG. 2 is a block diagram for
explaining the automatic wind noise reduction circuit 2 provided at the subsequent stage of the
automatic wind noise reduction circuit 1 shown in FIG. 1 for further reducing the residual wind
noise signal. . That is, the automatic wind noise reduction circuit 2 shown in FIG. 2 receives the
supply of the output signal from the automatic wind noise reduction circuit 1 shown in FIG. 1,
and further reduces the wind noise signal remaining in the supplied audio signal. It is for. The
terminals connected from the automatic wind noise reduction circuit 1 shown in FIG. 1 to the
automatic wind noise reduction circuit 2 shown in FIG. 2 have the same reference numerals as
the automatic wind noise reduction circuit 1 shown in FIG. To explain. As shown in FIG. 2, the
Rch digital audio signal from the automatic wind noise reduction circuit 1 shown in FIG. 1
supplied through the terminal 40 has one positive side terminal of the computing unit 50 and a
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delay unit 54. Are supplied to the positive terminal of the computing unit 57. Further, the digital
audio signal of Cch supplied from the automatic wind noise reduction circuit 1 shown in FIG. 1
supplied through the terminal 41 has the + terminal of the computing unit 50 and the + of the
computing unit 58 through the delay unit 55. It is supplied to the side terminal. Similarly, the Lch
digital audio signal supplied from the automatic wind noise reduction circuit 1 shown in FIG. 1
supplied through the terminal 42 is calculated via one of the plus terminals of the calculator 51
and the delay unit 56. The voltage is supplied to the positive terminal of the switch 59.
The addition output from the arithmetic unit 50 is supplied to the other + side terminal of the
arithmetic unit 51, and the addition output from the arithmetic unit 51 is supplied to the level
variable amplifier 53 through the LPF 52. The level variable amplifier 53 is controlled by the
wind noise level detection signal from the terminal 43 in the same manner as the level variable
amplifiers 32, 33, 34 of the automatic wind noise reduction circuit 1 shown in FIG. The output of
the level variable amplifier 53 is supplied to the negative terminal of each of the computing units
57, 58, 59, and the digital audio signal of Rch at the positive terminal, the digital audio signal of
Cch, the digital audio of Lch. The signals are respectively subtracted and output as Rch output,
Cch output and Lch output from the terminals 60, 61 and 62, respectively. The operation of the
automatic wind noise reduction circuit 2 shown in FIG. 2 will now be described. Using each of the
equations (5), (6) and (7) described above, when the wind noise is maximum, the output / input
ratio of the level variable 53 is set to 0.5, and the terminals 60, 61 , Rch output, Cch output and
Lch output are Rb, Cb and Lb, respectively, the Rch output Rb, Cch output Cb and Lch output Lb
are represented by the following equations (8) and (9) , (10) Rb = Rs + 0.5 (Rw + Lw + Cw)-0.5
(Rw + Lw + Cw) = Rs (8) Formula Cb = Cs + 0.5 (Rw + Lw + Cw)-0.5 (Rw + Lw + Cw) = Cs (9)
Formula Lb = Ls + 0.5 (Rw + Lw + Cw) -0.5 (Rw + Lw + Cw) = Ls (10) Therefore, the remaining
wind sound signals Rw, Lw, Cw are all canceled to obtain only the audio signals Rs, Cs, Ls.
Further, the delay units 54, 55, 56 compensate for the delay due to the LPF 52 on the main line
side, and the signal timing of the arithmetic units 57, 58, 59 is matched to further improve the
reduction effect. As described above, the Rch output, the Cch output, and the Lch output output
from the terminals 60, 61, 62 become an audio signal that does not include the wind sound
signal because the wind sound signal is canceled and if it is a video camera The signal is input to
recording system signal processing, and is recorded on a recording medium such as a tape
together with the video signal from the video signal system. Then, as described above, by making
the automatic wind noise reduction circuit compatible with three or more channels, wind noise
reduction processing can be easily performed at the front stage of the directivity calculation
circuit, It is possible to improve the performance and the freedom of system design.
Of course, it goes without saying that it can also handle two channels. In FIG. 2, the arithmetic
units 50 and 51 correspond to the second addition means, the LPF 52 corresponds to the third
extraction means, and the level variable amplifier 53 corresponds to the second gain control
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means. The computing units 57, 58, 59 correspond to the fourth subtracting means. Next, an
example of the multi-channeling of the audio signal processing system using the automatic wind
noise reduction circuit and the automatic wind noise reduction method according to the present
invention will be described. FIG. 3 is a diagram for explaining an example of multi-channelization
of the audio signal processing system in the case of having three microphones. In this example,
as shown in FIG. 3A, when three nondirectional microphones ML, MC, and MR are disposed, the
front right direction (hereinafter referred to as the FR direction). And the front center direction
(hereinafter referred to as the FC direction). And the front left direction (hereinafter referred to
as the FL direction). ), Rear left direction (hereinafter referred to as RL direction), and rear center
(hereinafter referred to as RC direction). And voices from the rear right (hereinafter referred to as
RR direction) are examples of multi-channeling having directivity. Each of the three microphones
ML, MC, and MR in this example has a nondirectional characteristic, and the direction of the
microphone sound receiving surface is not particularly limited, and forms a triangle as shown in
FIG. 3A. Will be placed. Assuming that the output signals from the respective microphones ML,
MC and MR are L, R and C, the signals in each pointing direction synthesized at this time are
expressed by the following equations. Front left direction (FL): L-α (C-φ) (11) Formula front
central direction (FC): (L + R) / 2-α (C-φ) (12) Front right direction (FR): R-α (C-φ) (13) Rear
left direction (RL): C-α (R-φ) (14) Rear central direction (RC ): C-α ((L + R) / 2-φ) (15) Rear
right direction (RR): C-α (L-φ) (16) Here, α is a predetermined multiplication The coefficient,
φ, is a predetermined time delay. These directivity patterns exhibit primary sound pressure
gradient (cardioid) characteristics in each direction. As described above, α represents a
multiplication coefficient for flattening the frequency characteristic, and φ represents a time
delay component corresponding to the physical distance between the arranged microphones.
Therefore, by applying the multi-channel automatic wind noise reduction circuit according to the
present invention to the output signals from the microphones ML, MR and MC, the wind
direction calculation process shown in FIG. 3B and also described above is performed. A
multichanneled audio signal having each directivity with reduced sound is obtained.
Further, it is also possible to calculate only the FL direction and the FR direction in FIG. 3 to
obtain Lch output and Rch output of stereo two-channel signal respectively. In this case, in the
latter stage of directivity calculation processing The conventional two-channel automatic wind
noise reduction processing of FIG. 5 can be inserted, but by inserting it in the front stage of the
directivity calculation processing as shown in FIG. Generally, directivity calculation processing is
processing for emphasizing the phase shift of the signals from the microphones. Therefore, for
wind sound signals having no correlation with the signals from the microphones, directivity
calculation processing is performed. If you let through, the level gets worse. Therefore, this
deterioration can be prevented by inserting the multi-channel automatic wind noise reduction
processing circuit according to the present invention at the front stage of the directivity
calculation processing. In the above-described embodiment, an example has been described in
which the automatic wind noise reduction processing is performed on the audio signals of three
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channels. However, the processing is also possible in the case of four or more channels. That is,
when there are N (N is an integer of 2 or more) audio channels, one audio channel is selected
from the N audio channels so as not to overlap, and this selected audio channel is selected. The
audio signals of the other audio channels are added to obtain N added signals, and the
corresponding added signal is subtracted from the audio signal of the selected audio channel to
obtain N subtracted signals, The band is limited so that the subtraction signal is in the wind noise
signal band. Then, by performing level adjustment (gain control) and subtracting the
corresponding subtraction signal of the N subtraction signals which are to be band-limited from
the speech signals of the N speech channels, The wind noise signal included in the audio signal of
each of the N audio channels can be reduced. Furthermore, as described above, from each of the
sound signals of the N sound channels in which the wind sound signal is reduced, the sound
signal of the sound signal of the N sound channels in which the wind sound signal is reduced is
added to the wind sound. Canceling the wind sound signal remaining in the target audio signal by
band limiting the signal to the frequency band of the signal and subtracting the level adjusted
signal, and obtaining only the target audio signal not including the wind sound signal Can.
Further, the level adjustment is not limited to that performed in accordance with the signal level
of the wind noise signal included in the audio signal, and may be fixedly performed in accordance
with the average level of the wind noise signal, Also, level adjustment may be performed
according to the selected stage according to the level for each predetermined stage, such as
strong, medium, or weak.
Further, in the embodiment described above, the band limitation of the audio signal of each audio
channel is performed at the stage before the computing units 26 and 39, the computing units 27
and 31, and the computing units 28 and 29. The present invention is not limited to this, and the
output signals of the computing units 29, 30, 31 may be band limited. Further, in the
embodiment described above, an example has been described in which the automatic wind noise
reduction processing is performed on the sound signal collected by the microphone, but the
present invention is not limited to this. Also at the time of reproduction of an audio signal from a
multi-channel recorded recording medium, automatic wind noise reduction processing is possible
as in the case shown in FIGS. As described above, according to the automatic wind noise
reduction circuit and the automatic wind noise reduction method of the present invention,
automatic wind noise reduction processing is performed on audio signals of three or more
channels. Therefore, there is a degree of freedom regardless of where to insert the automatic
wind noise reduction processing, and it is possible to cope with future multi-channeling. Further,
as the wind noise reduction processing can be divided into two stages as shown in FIGS. 1 and 2,
the circuit scale can be selected according to the necessity of the system. In addition, wind noise
reduction processing can be performed before the wind noise signal level is deteriorated by
performing wind noise reduction processing at the front stage of directivity computation
processing such as stereo processing processing, and the dynamic range of the signal at the rear
stage can be secured. It will be easier and system design easier. BRIEF DESCRIPTION OF THE
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DRAWINGS FIG. 1 is a diagram for describing an embodiment of an automatic wind noise
reduction circuit and an automatic wind noise reduction method according to the present
invention. FIG. 2 is a diagram for explaining an embodiment of an automatic wind noise
reduction circuit and an automatic wind noise reduction method according to the present
invention; FIG. 3 is a view for explaining an example of a multi-channel of an audio signal system
by arranging three nondirectional microphones; FIG. 4 is a diagram for explaining frequency
characteristics of a wind sound signal collected by a microphone mounted on a video camera.
FIG. 5 is a diagram for explaining an example of a conventional two-channel automatic wind
noise reduction circuit. [Description of the code] 1, 2 ... Automatic wind noise reduction circuit,
10, 11, 12 ... Microphone, 13, 14, 15 ... Amplifier, 16, 17, 18 ... ADC (analog / digital converter),
19 ... Arithmetic unit (For subtraction), 20, 22, 24 ... delay device, 21, 23, 25 ... LPF, 26, 27, 28 ...
arithmetic unit (for addition), 29, 30, 31 ... arithmetic unit (for subtraction), 32, 33, 34: Level
variable amplifier, 35, 36, 37: Arithmetic unit (for subtraction), 40: Rch terminal, 41: Cch
terminal, 42: Lch terminal, 43: Detection terminal, 50, 51: Arithmetic unit (for addition) , 52 ...
LPF, 53 ... level variable amplifier, 54, 55, 56 ... delay unit, 57, 58, 59 ... computing unit (for
subtraction), 60 ... Rch terminal, 61 ... Cch terminal, 62 ... Lch terminal, 121 ... LPF, 122 ...
amplifier, 123 ... Detector, 124 ... coefficient generator
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