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JPH07240991

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DESCRIPTION JPH07240991
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
microphone device capable of obtaining superdirectivity.
[0002]
2. Description of the Related Art Conventionally, in order to reduce unnecessary noise such as
background sound and to pick up only a desired sound, a microphone having directivity such as
unidirectionality is often used. In addition, it is also considered to apply an adaptive noise
canceler (ANC) to eliminate unnecessary noise and the like so that only desired voice can be
obtained.
[0003]
A microphone device to which this adaptive noise canceller is applied (hereinafter referred to as
an adaptive processing microphone device). ) Will be described with reference to FIG. The main
input signal input through the main input terminal 51 is supplied to the adder circuit 53 through
the delay circuit 52. Further, the reference noise signal n1 input through the reference input
terminal 54 is supplied to the addition circuit 53 through the adaptive filter circuit 55, and is
subtracted from the signal from the delay circuit 52. The subtraction output of the addition
circuit 53 is fed back to the adaptive filter circuit 55 and is derived to the output terminal 56.
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[0004]
The main input signal is a signal obtained by adding the desired signal S and the noise signal n0
uncorrelated thereto. On the other hand, the reference input noise signal n1 has no correlation
with the desired signal S, but has a correlation with the noise signal n0.
[0005]
The adaptive filter circuit 55 filters the reference input noise signal n1 and outputs a signal y
that approximates the noise signal n0. This signal y is subtracted from the main input signal in
the adder circuit 53. Therefore, the signal derived from the output terminal 56 approximates to
the desired signal S. The delay circuit 52 is inserted to compensate for the time delay required
for the adaptive processing operation in the adaptive filter circuit 55, the propagation time of the
filter, and other delays. Here, the main input signal supplied to the main input terminal 51 is
picked up by the main input microphone 57. The reference input noise signal n0 supplied to the
reference input terminal 54 is picked up by the reference input microphone 58.
[0006]
In this way, the adaptive processing microphone device can obtain sharp directivity, a signal very
close to the desired voice can be obtained as an output, and a good sound collection quality
substantially equal to or better than a superdirective microphone can be obtained. The present
invention can be realized not as a large-sized device but as a small-sized device.
[0007]
By the way, even if the above-mentioned adaptive processing microphone device is designed to
have flat sound pressure-frequency characteristics in a free sound field such as outdoors, this
microphone is used. It is known that when sound is collected in a room with a sounding sound
field (reverberation sound field or diffuse sound field), the bass range such as the surrounding
sound or noise is picked up as if it is expanded and it is difficult to hear ing.
[0008]
In this way, the sound field to be used is diffusive, there are many reverberations, and the
background noise level, which is the total noise of the system that exists regardless of the
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presence or absence of the transmission signal, is equal to or greater than the desired input
speech level. In this case, as a property of the adaptive processing microphone device, the
rejection rate of unnecessary noise and the like is limited, and it is difficult to obtain a good
sound collection quality.
[0009]
In particular, in an environment where background noise is incident, the adaptive processing
microphone device may operate to amplify background noise itself.
In addition, the directional characteristics of the output may be significantly impaired due to the
influence of background noise.
[0010]
That is, depending on various conditions of the real environment such as background noise, the
adaptive processing microphone device may interfere with its original operation and as a result,
directivity may be broken or background noise may be amplified. .
[0011]
The present invention has been made in view of the above circumstances, and it is an object of
the present invention to obtain a large reduction amount for the background noise even in the
environment where the background noise is incident, the diffuse sound field or the reverberation
sound field. It is an object of the present invention to provide a microphone device having high
sound collection quality, capable of obtaining a large amount of reduction for noise from
directions other than the desired direction.
[0012]
A microphone device according to the present invention subtracts an adaptive processing signal
obtained by adaptively processing an audio signal from a reference input microphone from a
main input microphone, and outputs the power of the subtraction output. Adaptive microphone
means for performing adaptive processing so as to minimize the above, directional microphone
means having fixed directivity, level detection means for detecting the levels of the output signals
of the adaptive microphone means and the directional microphone means The adaptive means
having a smaller output signal level according to the comparison result of the comparison means
for comparing the levels of the output signal of the adaptive microphone means and the
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directional microphone means detected by the level detection means; Switching means for
switching and outputting the output of the microphone means or the directional microphone
means To solve the above problem by.
[0013]
In this case, the directional microphone means may have a fixed directional characteristic by the
mixed output of the main input and the reference input.
[0014]
The switching means may select and output the output of the adaptive microphone means or the
directional microphone means according to the background noise detection output and the level
detection comparison output.
[0015]
The background noise detection output is detected by the background noise detection means.
Background noise is noise whose waveform is random, regardless of the presence or absence of a
transmission signal which is particularly noticeable in a reverberant sound field or a diffuse
sound field.
The background noise detection means detects background noise in the reverberant sound field
or the diffuse sound field using the property that the frequency characteristic changes in the case
of a non-directional microphone and in the case of a directional microphone. There is.
That is, in the case of a nondirectional microphone, the frequency characteristics hardly change
with the free sound field even in a reverberant sound field or a diffuse sound field, but in the case
of a directional microphone, in a reverberant sound field or a diffuse sound field It utilizes the
characteristic that the sound field sensitivity is high in the low range.
[0016]
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Further, the level detection means cuts out each output signal corresponding to each directional
characteristic of the adaptive microphone means and the directional microphone means with a
window of a fixed length as needed, and calculates the energy total in the cut-out section. It is
also good.
In this case, as windows used, there are various windows such as directional windows, Hanning
windows, Hamming windows and the like.
Then, the comparison means compares the total energy of the cut-out section, and the selection
means selects one of the output signals having the smallest output signal level according to the
comparison result of the comparison means. Do.
[0017]
The comparing means compares the levels of the output signals of the adaptive microphone
means and the directional microphone means detected by the level detecting means in the cutout section of a fixed length, and the selecting means outputs the smaller one according to the
result of the comparison. Since one of the output signals having the signal level is selected and
output, it is possible to output a voice in which noise from the direction excluding the desired
direction is most reduced, for each cutout section of the predetermined length.
In addition, even in an environment where background noise is incident, a large amount of
reduction can be obtained for the background noise, and a large amount of reduction can be
obtained for noise from directions other than the desired direction. And superdirectivity can be
obtained in a very compact configuration.
[0018]
Embodiments of the microphone device according to the present invention will be described
below with reference to the drawings.
First, as shown in FIG. 1, in the first embodiment, a main input microphone M1 for picking up a
desired voice, a reference input microphone M2 for picking up voice in a direction to be removed
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as noise, and Adaptive processing signal obtained by adaptively processing the sound signal from
the microphone M3 having the basic directivity and the microphone for reference input M2 is
subtracted from the microphone M1 for main input to minimize the power of the subtraction
output An adaptive processing unit 1 for performing adaptive processing, an energy calculating
unit 6 for calculating energy of an output from a microphone M3 having a fixed directivity and
the filter processing output of the adaptive processing unit 1, and the energy calculating unit 6
According to the result of the energy comparison in the comparator 3 which compares the
calculated energy and this comparator 3, the output with the smaller energy is selected, and only
the output signal is selected. A microphone device comprising and a changeover switch unit 4
outputs from the force terminal 5.
[0019]
Here, the main input microphone M1 and the reference input microphone M2 have the same
main axis. Also, the main axes of the microphones M3 having fixed directivity are the same as
those of the main axis.
[0020]
The adaptive processing unit 1 includes an adaptive filter circuit 8 to which the audio signal from
the reference input microphone M2 is supplied, and a subtraction circuit 7 that subtracts the
output signal of the adaptive filter circuit 8 from the desired audio signal of the main input
microphone M1. have. An output signal of the subtraction circuit 7 is fed back to the adaptive
filter circuit 8 and is also supplied to the changeover switch 4 and the energy calculating unit 6.
[0021]
In the microphone device of the first embodiment, the main input microphone M1 is an
omnidirectional microphone capable of collecting sound with almost uniform sensitivity to
sounds in all directions. The reference input microphone M2 is a unidirectional microphone
having sensitivity in the back direction, which is an angle of 180 °, when the direction of arrival
of the desired audio signal is an angle of 0 °.
[0022]
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The adaptive filter circuit 8 is controlled such that the reference input speech approximates the
speech as noise contained in the main input speech, as described later. By this, assuming that the
desired voice in the voice collected by the main input microphone M1 and the noise are
uncorrelated, in the subtraction circuit 7, the noise signal collected by the reference input
microphone M2 is the main input The speech signal from the microphone M1 is subtracted and
removed, and only the desired signal is obtained from the subtraction circuit 7.
[0023]
That is, this configuration is configured by applying an adaptive noise canceller to which the
output signal of the main input microphone M1 is supplied as the main input and the output
signal of the reference input microphone M2 is supplied as the noise as the reference input.
There is. Hereinafter, the adaptive processing unit 1 to which the adaptive noise canceller is
applied is referred to as an adaptive microphone unit 1.
[0024]
In this case, the main input voice from the main input microphone M1 is a desired voice signal S
from the front direction of the arrow AR and a voice signal from the back direction considered to
be uncorrelated with this as shown in FIG. The noise n0 is added. On the other hand, the
reference input audio signal n1 from the reference input microphone M2 has no correlation with
the desired audio signal, but has a correlation with the noise n0. The adaptive filter circuit 8
filters the reference input speech signal n1 to output a signal y, and the adaptive algorithm
works to minimize the subtraction error e which is the output of the subtraction circuit 7.
[0025]
Now, the desired input signal S, the noise signal n0, the reference input speech signal n1 and the
output signal y are statistically stationary. Further, assuming that the average value of these
signals is 0, the residual output e becomes e = S + n0−y (1). The expectation value E [e2] of the
square of the residual output e in the equation (1) is E [e2] = E because the desired input signal S
has no correlation with the noise signal n0 and the output signal y. [S2] + E [(n0-y) 2 + 2 E [S (n0y)] = E [S2] + E [(n0-y) 2] (2). Assuming that the adaptive filter circuit 8 converges, the adaptive
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filter circuit 8 updates the adaptive filter coefficients such that E [e2] is minimized. At this time,
since E [S2] is not affected, the minimum value Emin [e2] is Emin [e2] = E [S2] + Emin [(n0−y) 2]
(3)
[0026]
Here, the fact that E [e2] is minimized is that E [(n0-y) 2] is minimized. Thus, the filter output y is
the best least squares estimate of the noise signal n0. When E [(n0-y) 2] is minimized, E [(e-S) 2]
is also minimized. これは、e−S=n0−yであるためである。 That is, adjusting the filter to
minimize the total output power is equivalent to the residual output e being the best least
squares estimate of the desired signal S.
[0027]
Although the residual output e generally has some noise remaining in the desired signal S, the
output noise is given by n 0 −y, so minimizing E [(n−y) 2] is an output of It is equivalent to
maximizing the signal to noise ratio.
[0028]
Next, a specific example of the adaptive filter circuit 8 is shown in FIG.
In this embodiment, as shown in FIG. 3, an FIR filter type adaptive linear combiner 60 is used.
The adaptive linear combiner 60 includes a plurality of delay circuits 611, 612,... 61m (m is an
integer) each having a delay time Z-1 of unit sampling time, a reference input noise signal n1,
and each delay circuit. .. 62m and the outputs of the weighting circuits 620, 621, 622,... 62m for
multiplying the output signals of 611, 612. And an adder circuit 63. The output signal y of the
adding circuit 63 is supplied to the subtracting circuit 7 of FIG. 1 through the output terminal 64.
[0029]
The weighting factors supplied to the weighting circuits 620, 621, 622,... 62m are, for example,
residual signals e supplied from the subtraction circuit 7 shown in FIG. 1 through the input
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terminal 66 in the LMS arithmetic circuit 65 comprising a microcomputer. And the reference
input audio signal n1. The algorithm executed by this LMS arithmetic circuit 65 is as follows.
[0030]
Now, as also shown in FIG. 3, the input vector Xk at time k is Xk = [x0k, x1k, x2k ... xmk] T (4),
the output is yk, and the weighting coefficient is wjk (j Assuming that = 0, 1, 2 ... m), the
relationship between input and output is
[0032]
【0032】となる。
[0033]
Then, if the weighting vector Wk at time k is defined as Wk = [w0k, w1k, w2k ... wmk] T (6), the
input / output relationship shown in the above equation (5) is yk = XkT · Wk (7)
Assuming that the desired response is dk, its differential output (residual output) ek is ek =
dk−yk = dk−XkT · Wk (8)
[0034]
In the LMS (least mean square) method, updating of the weight vector is performed according to
the equation Wk + 1 = Wk + 2μ · ek · Xk (9).
Here, μ is a gain factor (step gain) that determines the speed and stability of adaptation.
[0035]
Thus, the subtraction circuit 7 obtains an audio signal mainly composed of the desired audio
signal from which noise, in this example, the audio signal from the back direction has been
removed.
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[0036]
Thus, the adaptive filter circuit 8 operates to minimize the output power by updating the weight
vector in the manner described above.
[0037]
By the way, in order to reduce the noise in the main input using the reference input by the
adaptive processing as described above, it is necessary for the desired voice and the reference
noise to be uncorrelated, as described above.
For this reason, conventionally, with this type of adaptive noise canceller, the reference input
microphones should be designed with soundproofing, placed as close as possible to the noise
source, and not for the main input, so as not to pick up the desired voice as the reference input.
Measures such as keeping away from the microphone are being taken.
However, this makes the system large and difficult to move.
[0038]
On the other hand, in the microphone device of the first embodiment, the desired voice and noise
are distinguished by the arrival direction of voice. The main input microphone M1 is
omnidirectional so as to have a directional characteristic that can pick up voice from the desired
voice arrival direction, and the reference input microphone M2 has no sensitivity in the desired
voice arrival direction, or It is considered to be unidirectional with low sensitivity directivity
characteristics, and the desired voice in the voice collected by the main input microphone M1
and the noise collected by the reference input microphone M2 are uncorrelated To be
[0039]
Next, the microphone M3 having a fixed directivity is a microphone having a fixed directivity
relatively close to superdirective characteristics. In the first place, what is required of the fixed
directional microphone is a so-called sharp directivity characteristic that the sensitivity in the
other direction is better as the sensitivity is lower in the forward direction (desired direction). In
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this first embodiment, as the microphone M3 having this fixed directivity, for example, a hypercardioid microphone or a sharp directional microphone of a super-cardioid microphone is used.
Hereinafter, this microphone M3 is referred to as a sharp directional microphone M3.
[0040]
The output signals of the sharp directional microphone M 3 and the adaptive microphone unit 1
are supplied to the energy calculating unit 6 and the changeover switch unit 4. Hereinafter, the
energy calculation unit 6, the changeover switch unit 4, and the comparison unit 3 will be
described.
[0041]
The energy calculation unit 6, which is a level detection unit, cuts out the output signals of the
sharp directional microphone M3 and the adaptive microphone unit 1 at any time with a window
having a fixed length, and calculates the sum of the energy in the cut section ing. The sum of the
energy is the sum of all square values of each sample of data in the cutout section. As windows
used in this case, various windows such as square windows, Hanning windows, Hamming
windows, etc. can be used. The window length is a very short time, for example, about 42 msec.
[0042]
The comparator 3 compares the powers of the output signals of the sharp directional
microphone M3 and the adaptive microphone unit 1 calculated by the energy calculation unit 6
in the cutout window section of a fixed length, and the output signal of the smaller energy is
which Information is supplied to the changeover switch 4.
[0043]
In response to the information supplied from the comparator 3, the changeover switch unit 4
outputs an output signal having a smaller energy from the output terminal 5 in the cutout
window section.
[0044]
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Here, the reason why the changeover switch unit 4 selects the output signal having small energy
is that the output signal having small energy contains no noise component.
As the noise signal, in addition to the background noise, there is a background noise regardless
of the presence or absence of the transmission signal which is remarkably observed in the diffuse
sound field or the reverberation sound field.
This background noise is uncorrelated in consideration of the case where the waveform is
random and, for example, sound is collected in two directions. Therefore, if it is intended to
reduce the overall noise only by the adaptive microphone unit 1, background noise with a
random waveform will be added by the subtraction circuit 7. Therefore, in this first embodiment,
the energy levels of the output signals are compared, and the output signal with the smaller
energy level (the output signal of the adaptive microphone unit 1 or the microphone M3) is
output.
[0045]
Therefore, the microphone device according to the first embodiment can output, for each cut-out
section of the predetermined length, a voice in which noise and background noise from the
direction excluding the desired direction are most reduced. For this reason, in this first
embodiment, although the configuration is small, even if the directional characteristics of the
output of the adaptive microphone unit 1 are significantly impaired or the background noise is
amplified due to the influence of the background noise or the like, A signal with sharp directivity
can be temporarily output from the directional microphone, and superdirectivity can be obtained.
[0046]
Next, a second embodiment will be described with reference to FIG. Like the configuration of the
first embodiment shown in FIG. 1, the second embodiment comprises an adaptive microphone
unit 1, an energy calculating unit 6, a comparator 3, and a changeover switch 4. , And the sharp
directional microphone M3 shown in FIG. 1 is not provided. A directional microphone unit 9 is
provided instead of the sharp directional microphone M3.
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[0047]
The directional microphone unit 9 mixes the main input from the main input microphone M1
and the reference input from the reference input microphone M2 to obtain an output signal
similar to that output by the sharp directional microphone M3. ing. That is, the subtraction
circuit 11 subtracts the reference input amplified by the amplifier 10 from the main input.
[0048]
The reference input picked up by the reference input microphone M2 is a noise signal from the
back direction at an angle of 180 ° with respect to the desired voice signal arrival direction. For
example, when a value obtained by multiplying the noise signal by -1.5 in the amplifier 10 is
subtracted from the desired voice signal as the main input, an output signal of polar pattern as
shown in FIG. 5 can be obtained. The polar pattern as shown in FIG. 5 represents sharp
directivity, and the directional microphone unit 9 of the second embodiment has an output
equivalent to that of the sharp directional microphone 3 used in the first embodiment. It turns
out that you can get it.
[0049]
The output signals of the directional microphone unit 9 and the adaptive microphone unit 1 are
supplied to the energy calculation unit 6 and the changeover switch 4.
[0050]
The energy calculating unit 6 cuts out the output signals of the directional microphone unit 9
and the adaptive microphone unit 1 at any time with a window having a fixed length, and
calculates the sum of the energy in the cutout section.
The sum of the energy is the sum of all square values of each sample of data in the cutout
section. As the window used in this case, various windows such as a square window, a Hanning
window, and a Hamming window can be used as in the first embodiment.
[0051]
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The comparator 3 compares the powers of the output signals of the directional microphone unit
9 and the adaptive microphone unit 1 calculated by the energy calculation unit 6 in the cutout
window section of a fixed length, and the output signal of the smaller energy is which
Information is supplied to the changeover switch 4.
[0052]
In response to the information supplied from the comparator 3, the changeover switch unit 4
outputs an output signal having a smaller energy from the output terminal 5 in the cutout
window section.
[0053]
The effect at the time of background noise incidence in the second embodiment will be described
below with reference to FIG.
In FIG. 6, when female voice comes from the desired direction, while another female voice and
male voice come from the side and the back as noise voice, respectively, the background noise of
the same level as each voice. Is a diagram showing the effect in the situation where
A on the horizontal axis indicates the case of only the adaptive microphone unit 1, and B
indicates the effect of the second embodiment. A triangle point connected by a straight line SN
indicates the amount of noise reduction from the direction excluding the desired voice arrival
direction. Also, the black points connected by the straight line SB indicate the reduction amount
of background noise. With regard to the reduction of the noise voice, although the adaptive
microphone unit 1 alone can obtain a considerable reduction amount, the reduction of the
background noise is not reduced but is increased. Compared to this, in the second embodiment,
the background noise can be significantly reduced, and the reduction amount of the noise sound
also exceeds that in the case of the adaptive microphone unit 1 alone.
[0054]
Therefore, the microphone device according to the second embodiment can output, for each cutout section of the predetermined length, a voice in which noise and background noise from the
direction excluding the desired direction are most reduced. Therefore, although the second
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embodiment has a further smaller configuration, the directional characteristics of the output of
the adaptive microphone unit 1 may be significantly impaired or the background noise may be
amplified due to the influence of the background noise or the like. A signal having sharp
directivity can be temporarily output from the directivity micron unit 9, and superdirectivity can
be obtained.
[0055]
Next, a third embodiment will be described with reference to FIG. In the third embodiment, the
adaptive microphone unit 1, the directional microphone unit 9, the energy calculating unit 6, the
comparator 3, and the changeover switch 4 are the same as the configuration of the second
embodiment shown in FIG. And further comprises a comparator 12 which serves to detect the
background noise level.
[0056]
The comparator 12 compares the main input from the main input microphone M1 with the
reference input from the reference input microphone M2, and detects the background noise level
from the comparison result. That is, the comparator 12 is a background noise detection means.
Background noise is noise whose waveform is random, regardless of the presence or absence of a
transmission signal which is particularly noticeable in a reverberant sound field or a diffuse
sound field. The frequency characteristics in the reverberant sound field or diffuse sound field of
the main input microphone M1 which is a nondirectional microphone hardly change with that in
the free sound field, but the reverberation sound of the reference input microphone M2 which is
a directional microphone The frequency response in the field or diffuse sound field is high in the
bass range. By utilizing such a property, the comparator 12 detects background noise.
Specifically, when it is detected in the comparator 12 that the level of the output signal supplied
from the reference input microphone M2 is high, the comparator 12 indicates that the
changeover switch 4 is an environment where there is much background noise. Supply.
[0057]
Then, the changeover switch 4 having received the background noise high level information
adjusts the switching to the output signal selection from the directional microphone unit 9.
[0058]
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On the other hand, when the comparator 12 does not detect a high level background noise, the
changeover switch 4 selectively outputs the output signal from the adaptive microphone unit 1.
[0059]
Here, the operation of the energy calculating unit 6, the comparator 3, and the changeover
switch 4 will not be described.
The configuration around the changeover switch 4 can also be a specific example as shown in
FIG.
That is, in FIG. 8, the state detection unit 24 determines the detection signal from the comparator
12 and the detection signal from the comparator 3 to control the switching of the changeover
switch 4. However, when there is much background noise, the state detector 24 gives priority to
the comparison result of the comparator 12 even if the energy of the output of the adaptive
microphone unit 1 is smaller than that of the directional microphone unit 9. Do the action.
[0060]
A specific example of the inside of the changeover switch 4 used in the third embodiment is
shown in FIG. As shown in FIG. 9, when the background noise level is high, the switch SW2
controlled by the detection result of the comparator 12 can be prioritized, so the output of the
directional microphone unit 9 is output from the output terminal 5 can do.
[0061]
Further, the changeover switch 4 may be a specific example as shown in FIG. Also in this case,
priority is given to switching of the switch SW2.
[0062]
From the above, in this third embodiment, although the configuration is small, the directivity
characteristic of the output of the adaptive microphone unit 1 is significantly impaired due to the
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influence of the background noise or the background noise is amplified. It is possible to
temporarily output a signal having sharp directivity from the sexing micro part 9 and obtain
superdirectivity.
[0063]
The microphone device according to the present invention is not limited to the first to third
embodiments. For example, the comparator not only compares the sum of the energy of the
output signal, but also the amplitude of the output signal, The peak values may be compared.
Further, the level detection means may detect the level of each output signal instantaneously.
[0064]
Further, the microphone device described above is applicable not only to be used as a sound
pickup microphone device of a camera integrated type VTR, but also applicable to all microphone
devices such as a professional video camera and a measurement microphone device.
[0065]
The microphone apparatus according to the present invention subtracts the adaptive processing
signal obtained by adaptively processing the audio signal from the reference input microphone
from the main input microphone to minimize the power of the subtraction output. Adaptive
microphone means for performing adaptive processing, directional microphone means having
fixed directivity, level detection means for detecting the levels of the output signals of the
adaptive microphone means and the directional microphone means, and the level detection The
adaptive microphone means or the adaptive microphone means having the smaller output signal
level according to the comparison result of the comparison means comparing the level of the
output signal of the adaptive microphone means detected by the means and the directional
microphone means Because it has switching means for switching the output of the directional
microphone means and outputting it, The most reduced audio noise from directions other than
the direction can be outputted for each cut section of the fixed length.
In addition, even in an environment where background noise is incident, a large amount of
reduction can be obtained for the background noise, and a large amount of reduction can be
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obtained for noise from directions other than the desired direction. And superdirectivity can be
obtained in a very compact configuration.
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