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JPH0514989

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DESCRIPTION JPH0514989
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
audio signal processing apparatus for processing audio signals.
[0002]
2. Description of the Related Art Conventionally, as an apparatus for processing an audio signal,
an audio signal is formed by converting audio into an electrical signal by a microphone or the
like, and the formed audio signal is recorded on a recording medium by a tape recorder or the
like. There is a signal recording device.
[0003]
In the above-described audio signal recording apparatus, the frequency characteristic of an audio
signal amplifier circuit for amplifying an audio signal generated from a microphone is often
substantially constant. In this case, when the wind or the like hits the microphone, the audio to
be recorded In order to prevent the influence of the wind by mounting a wind screen or the like
on the microphone, the sound of the wind was mixed in as noise and the voice signal was
deteriorated.
[0004]
Also, since noise generated by the above-mentioned wind noise is a low frequency signal in terms
of frequency, in recent years, a switch for switching frequency characteristics to an audio signal
amplifier circuit can be used so that low frequency components can be removed from the audio
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1
signal. In the case where there is wind, the operator operates the changeover switch to operate
the audio signal amplifier circuit so as to remove the low frequency components of the audio
signal, thereby preventing the influence of the wind.
[0005]
However, in the case of the above-mentioned conventional apparatus, there is a problem that the
apparatus becomes large in size when the influence of the wind is prevented by the wind screen.
[0006]
When the operator operates the change-over switch to remove the low-frequency component of
the audio signal by operating the audio signal amplifier circuit to prevent the influence of the
wind, the operator can detect the presence or absence of the wind. Judging, it is very difficult to
operate the changeover switch and there is a possibility of erroneous operation.
[0007]
That is, in order to determine how much the effect of wind sound is on the operator, it is
necessary to constantly monitor the sound collected by the microphone, which is inconvenient
for the operator.
[0008]
In addition, when the changeover switch is operated without monitoring the sound, recording is
performed, for example, if the low-frequency component of the audio signal is not removed
without operating the changeover switch although the wind hits the microphone. The level of
wind sound is higher than the level of the voice, and the AGC (Auto Gain Controller) function in
the voice signal amplification circuit lowers the level of the entire voice collected by the
microphone by the wind noise. In addition, although the wind is not hit to the microphone, if the
change switch is operated to remove the low frequency components of the audio signal, the low
frequency of the sound collected by the microphone is kept. Because the frequency components
are always removed, the sound quality of the audio being recorded Become impaired is it.
[0009]
The present invention solves the above-mentioned problems, and provides an audio signal
processing apparatus capable of easily processing audio without being affected by noise such as
wind with a simple configuration without increasing the size of the apparatus. To aim.
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2
[0010]
An audio signal processing apparatus according to the present invention receives a first audio
signal, changes the frequency characteristics of the input first audio signal, and outputs the first
frequency characteristic variable. Means, a second frequency characteristic varying means for
inputting a second audio signal, changing a frequency characteristic of the input second audio
signal, and outputting the second audio signal, and the first audio signal and the second audio
signal input. Control means for controlling the characteristics of the first and second frequency
characteristic variable means in accordance with the level of the low frequency component of the
difference signal with the voice signal of A signal is input, the frequency characteristic of the
input first audio signal is changed, and the first frequency characteristic variable means for
outputting and the second audio signal are input, and the frequency of the input second audio
signal is input. Second frequency characteristic changing means for changing characteristics and
outputting The first and second frequency characteristics are variable according to the level of
the low frequency component of the difference signal between the first voice signal and the
second voice signal and the level of the middle frequency component of the sum signal. And
control means for controlling the characteristics of the means.
[0011]
According to the above-described configuration, it is possible to easily process voice without
being affected by noise such as wind with a simple configuration without increasing the size of
the device.
[0012]
The present invention will now be described by way of examples of the present invention.
[0013]
FIG. 1 is a view showing a schematic configuration of an audio signal recording apparatus to
which the present invention is applied as a first embodiment of the present invention.
[0014]
In FIG. 1, reference numerals 1 and 2 denote microphones which convert sound into an electric
signal (i.e., sound signal) and output the same; 1 is a left microphone and 2 is a right microphone.
[0015]
Reference numerals 3 and 4 denote variable filters for changing the frequency characteristics of
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audio signals respectively output from the microphones 1 and 2. Reference numeral 17 denotes
voltage control amplifiers 5 and 6, detection circuits 7 and 8, time constant circuit 10, and
comparison circuit 11. An AGC (Auto Gain Control) circuit configured to amplify the audio signal
output from the variable filters 3 and 4 according to the level, and 12, an audio signal whose
level is controlled by the AGC circuit 17 is A recording unit for recording on a recording medium
such as tape, 13 is a subtractor for forming a difference signal of audio signals output from the
microphones 1 and 2, and 14 is a low band of the difference signal output from the subtractor
13. A band pass filter (BPF) for extracting frequency components, 15 amplifies low frequency
components of the difference signal extracted in the BPF 14 Amplifier 16 detects a low
frequency component of the difference signal amplified by the amplifier 15 and outputs a low
frequency detection signal. A frequency 9 detects the low frequency detection signal output from
the detection circuit 16. When the frequency characteristics of the audio signal are changed by
the variable filters 3 and 4 whose variable characteristics are controlled, an attack recovery time
is set to prevent the change in the frequency characteristics of the audio signal from being
disturbed by hearing. Time constant circuit.
[0016]
In FIG. 1, voices collected by the microphones 1 and 2 are converted into electric signals (ie,
voice signals) and supplied to the variable filters 3 and 4 and the subtractor 13.
[0017]
The subtractor 13 forms a difference signal of the audio signals supplied from the microphones 1
and 2, and the BPF 14 extracts the low frequency component of the difference signal and
supplies it to the amplifier 15.
[0018]
Then, the low frequency component of the difference signal amplified by the amplifier 15 is
supplied to the detection circuit 16, the level of the low frequency component of the difference
signal is detected by the detection circuit 16, and the time constant circuit 9 is detected as a low
frequency detection signal. Supplied.
[0019]
FIG. 2 is a diagram showing the frequency spectrum distribution of the audio signal outputted
from the microphones 1 and 2. In the figure, A indicates the frequency spectrum distribution of
the voice to be recorded (hereinafter referred to as general voice), and W indicates It shows the
frequency spectrum distribution of voice (hereinafter referred to as wind noise) indicating wind.
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[0020]
As shown in FIG. 2, the frequency spectrum of general speech is distributed around 1 KHz except
in special cases, and the frequency spectrum of wind noise is distributed in a low frequency band
of 200 Hz or less.
[0021]
FIG. 4 is a diagram showing a polar pattern of 1 KHz when the microphones 1 and 2 are
configured as a one-point stereo microphone.
[0022]
As shown, the microphone 1 for the left side has directivity in the left front direction, and the
microphone 2 for the right side has directivity in the right front direction.
[0023]
Further, FIG. 5 is a diagram showing a polar pattern of a frequency lower than the condition in
FIG. 4 of the one-point stereo microphone, for example, 30 Hz, and as shown, compared to the
case of 1 KHz shown in FIG. Sex becomes duller, becomes closer to the directivity of a
monophonic microphone, and the correlativity of the audio signal outputted from each of the
microphones 1 and 2 becomes high.
[0024]
As can be seen from the above-described frequency spectrum distribution of voice and wind
noise, and the directional characteristics of the microphone, in the case of low frequency general
voice, the correlation between the voice signals respectively output from the microphones 1 and
2 is high. When the low frequency component is extracted by the BPF 14 from the difference
signal of the audio signals output from the microphones 1 and 2 output from the subtractor 13
of FIG. 1, the level of the signal extracted by the BPF 14 decreases. In the case of low frequency
wind noise generated by the wind hitting a microphone, the audio signals respectively output
from the two microphones 1 and 2 have low correlation, so the subtractor 13 and the BPF 14
extract The level of the low frequency component of the difference signal increases.
[0025]
Therefore, in the present embodiment, as shown in FIG. 1, the difference signal of the audio
signals outputted from the microphones 1 and 2 is formed by the subtractor 13, and the formed
difference signal is shown in FIG. The audio signal output from the microphones 1 and 2 is
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supplied according to the level of the low-pass detection signal obtained by amplifying the signal
output from the BPF 14 having the For example, as shown in a of FIG. 8, the attenuation of the
low frequency is changed, or the cutoff frequency of low is changed as shown in b of FIG. By
doing so, it is possible to control the gain of the low frequency component of the audio signal in
response to low frequency wind noise without much reaction to low frequency general voice, so
only wind noise The influence of It is possible to perform.
[0026]
As described above, the low frequency detection signal output from the detection circuit 16 is
supplied to the time constant circuit 9, where the low frequency detection signal supplied from
the detection circuit 16 is integrated by a capacitor or the like, When the level of the integrated
signal exceeds a predetermined threshold value, the pass characteristic of the variable filters 3
and 4 is continuously changed in the direction to attenuate the low frequency components
according to the level of the integrated signal, and The variable filters 3 and 4 attenuate the wind
noise signal component mixed in the voice signal so that the user can not audibly hear it.
[0027]
Then, the audio signal whose wind noise signal component is attenuated in the variable filters 3
and 4 is level-limited by the AGC circuit 17 so as not to exceed a predetermined level, and then
recorded in the recording medium such as magnetic tape in the recording unit 12 Ru.
[0028]
The AGC circuit 17 is composed of voltage control amplifiers 5 and 6, detection circuits 7 and 8,
a comparator 11 and a time constant circuit 10 as shown in FIG. 1, and supplied from the
variable filters 3 and 4. An audio signal is amplified by the voltage control amplifiers 5 and 6 and
supplied to the recording unit 12, and the audio signals output from the voltage control
amplifiers 5 and 6 are detected by detection in the detection circuits 7 and 8. The signal is
supplied to the comparison circuit 11.
[0029]
The comparison circuit 11 compares the levels of the detection signals supplied from the
detection circuits 7 and 8 respectively, and detects the larger detection signal as the control
signal of the voltage control amplifiers 5 and 6 via the time constant circuit 10. The control
amplifiers 5 and 6 are supplied.
[0030]
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Then, when the level of the detection signal to be supplied exceeds a predetermined level, the
voltage control amplifiers 5 and 6 decrease the gain for the input audio signal according to the
level, and the voltage control amplifiers 5 and 6 receive An audio signal whose level is limited so
as not to exceed a predetermined level is output and supplied to the recording unit 12.
[0031]
The time constant circuit 10 has a detection signal output from the comparison circuit 11 with a
predetermined time constant so that the voltage control amplifiers 5 and 6 limit the level of the
audio signal so as not to be aurally inaudible. The voltage control amplifiers 5 and 6 are supplied.
[0032]
As described above, in the present embodiment, the frequency of the variable filter for
attenuating the low frequency component in the audio signal according to the level of the low
frequency component of the difference signal of the audio signal respectively output from the
two microphones. By changing the characteristics, it is possible to attenuate the low frequency
components of the audio signal by reacting sensitively to low frequency wind noise without much
reaction to low frequency general speech As shown in FIG. 1, it is possible to make the wind
noise signal component mixed in the signal aurally inconspicuous, and even if AGC is applied
before recording on the recording medium as shown in FIG. It becomes possible to prevent the
level of the general speech signal from being attenuated.
[0033]
FIG. 6 is a view showing a schematic configuration of an audio signal recording apparatus to
which the present invention is applied as a second embodiment of the present invention.
[0034]
The same reference numerals as in the first embodiment shown in FIG. 1 denote the same parts,
and a detailed description thereof will be omitted.
[0035]
In FIG. 6, reference numeral 18 denotes an adder for forming a sum signal of audio signals
output from the microphones 1 and 2, and 19 an intermediate frequency component of the sum
signal output from the adder 18. BPF 20 is an amplifier for amplifying the mid-frequency
component of the sum signal extracted in the BPF 19, 21 is for detecting mid-frequency
components of the sum signal amplified in the amplifier 20, and a mid-range detection signal is
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output A detection circuit 22 compares the middle band detection signal output from the
detection circuit 21 with the low band detection signal output from the detection circuit 16, and
outputs a signal corresponding to the comparison result, The signal output from the comparison
circuit 22 is supplied to the variable filters 3 and 4 through the time constant circuit 9.
[0036]
In the first embodiment, the detection of the mixed state of the wind noise signal component in
the audio signal output from the microphones 1 and 2 is performed by the level of the low
frequency component of the difference signal of the audio signal output from the microphones 1
and 2 respectively. In the second embodiment, two microphones 1 and 2 are used to reliably
prevent low frequency general audio signals from being erroneously detected as wind noise
signal components. The difference signal of the audio signal to be output is formed by the
subtractor 13 and the sum signal is formed by the adder 18, and from the formed difference
signal, the BPF 14 having a low pass frequency band shown by B in FIG. The low-frequency
component is extracted from the formed sum signal by the BPF 19 having a mid-pass frequency
band shown by C in FIG. 7 and the low-frequency component of the difference signal and the
sum signal are extracted. The high frequency components are amplified by the amplifiers 15 and
20 respectively and then detected by the detection circuits 16 and 21. The comparison circuit 22
detects the level of the low band detection signal of the difference signal and the level of the mid
band detection signal of the sum signal. By comparing and supplying a signal according to the
comparison result to the variable filters 2 and 3 through the time constant circuit 9, for example,
the comparison circuit 22 lowers the difference signal from the level of the mid-range detection
signal of the sum signal. When it is detected that the level of the detection signal is greater than
the predetermined level, the frequency characteristics of the variable filters 3 and 4 are changed
so as to attenuate the low frequency components in the audio signal.
[0037]
Also, when the level of the mid-range detection signal of the sum signal is large, even if the lowpass detection signal of the difference signal due to wind noise indicates a certain level, it is
determined that the level itself of the general audio signal is large. Since the frequency
characteristics of the filters 3 and 4 are not changed, the general audio signal can be recorded
without being affected by wind noise.
[0038]
In the second embodiment described above, the low frequency component of the difference
signal of the audio signal respectively output from the two microphones 1 and 2 and the mid
frequency component of the sum signal are extracted, and the detection signals of both
frequency components are extracted. Although the frequency characteristic of the variable filter
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for attenuating the low frequency components in the audio signal is controlled according to the
level difference, the detection signal of the low frequency components of the difference signal
and the middle high region of the sum signal are controlled. Comparison of the respective levels
of the difference in level with the detection signal of the frequency component, or the detection
signal of the low frequency component of the difference signal, the detection signal of the middle
frequency component of the sum signal, and the detection signal of the high frequency
component of the sum signal Depending on the result, the frequency characteristics of the
variable filter may be controlled.
[0039]
As described above, according to the level of the low frequency component of the difference
signal of the audio signal respectively output from the two microphones, the frequency
characteristic of the variable filter for attenuating the low frequency component in the audio
signal is changed. By configuring in the same manner, the wind noise signal component mixed in
the audio signal can be audibly inconspicuous.
[0040]
Furthermore, in the second embodiment, the level of the low-frequency component of the
difference signal of the audio signal respectively output from the two microphones is compared
with the level of the mid-frequency component of the sum signal. When the level of the lower
frequency component is larger than the predetermined level, the frequency characteristic of the
variable filter for attenuating the low frequency component in the audio signal is changed to
change the wind in the audio signal. When the noise component is automatically reduced, it is
possible to prevent the occurrence of a malfunction due to low frequency general speech.
[0041]
In each of the above-described embodiments, the frequency of the variable filter that attenuates
the low frequency component in the audio signal according to the level of the low frequency
component of the difference signal of the audio signal respectively output from the two
microphones. The characteristic of the low frequency component of the difference signal is
compared with the level of the low frequency component of the sum signal and the level of the
low frequency component of the sum signal is compared with the level of the low frequency
component of the sum signal. If the above is large, the wind noise component in the audio signal
is automatically reduced by changing the frequency characteristic of the variable filter that
attenuates the low frequency component in the audio signal. Instead of attenuating the low
frequency components in the audio signal, the medium high frequency components of the audio
signal are lifted by an equalizing circuit or the like, and the high frequency components of the
audio signal are low frequencies. The component may be configured so as to be relatively
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attenuated state.
[0042]
As described above, according to the present invention, an audio signal can be easily processed
with a simple configuration without being affected by noise such as wind and the like, according
to the present invention. It becomes possible to provide a processing device.
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