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JPH1118186

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DESCRIPTION JPH1118186
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
primary pressure gradient microphone having two types of unidirectional characteristics using a
plurality of nondirectional microphone units, which is excellent in the ability to reduce noise
components, and is small in size The present invention relates to a technology that contributes to
the conversion, for example, to a technology that is effective when applied to a primary pressure
gradient microphone for vehicles.
[0002]
The prior application by the present applicant (Japanese Patent Application No. 62-147476,
Japanese Utility Model Application No. 64-52393) is a single application using two
omnidirectional microphone units having substantially the same performance. A primary
pressure gradient microphone is disclosed that achieves unidirectionality. This primary pressure
gradient microphone is in principle substantially the same as the configuration of FIG. 2, and two
nondirectional microphone units M1 and M2 are arranged at an interval of distance d, and the
output of the microphone unit M2 is delayed. The circuit 2 is configured to delay by τ2 (τ2:
delay amount converted to distance), and to take out the difference between the delayed output
ed2 and the output e1 of the microphone unit M1.
[0003]
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1
Assuming that a sound comes from the direction of the angle θ with respect to the axial
direction of the two microphone units M1 and M2 in the microphone configured in this way, the
output Vm of the microphone is Vm (k, θ) = e1−ed2 It is given by: 2 · e1 · sin {k (τ 2 + d · cos
θ) / 2}. However, k = 2π / λ (λ: wavelength of sound), and the sound arriving at the
microphone unit is a sine sound wave (sound wave of sine waveform). From the above equation,
by setting τ 2 appropriately smaller than d, the directivity characteristics as shown in FIG. 3 can
be obtained.
[0004]
Here, in order to facilitate understanding, the principle of the primary pressure gradient
microphone will be described qualitatively with reference to FIG. The case of τ2 = d, θ = 0 is
taken as an example. The observation point corresponding to the output e1 (a) by the
microphone unit M1 for the sound coming from the Sa direction is Pe1 (a), and the observation
point corresponding to the delay output ed2 (a) on the microphone unit M2 side is apparently
Ped2 (a) It is. The observation point according to the output e1 (b) by the microphone unit M1
for the sound coming from the opposite direction Sb is Pe1 (b), and the observation point
according to the delay output ed2 (b) on the microphone unit M2 side is apparently Ped2 (b). As
apparent from the figure, since the observation points Pe1 (b) and Ped2 (b) are at the same
position, e1 (b) = ed2 (b). Therefore, the output Vm of the microphone is Vm (k, θ) = e1 (a) + e1
(b) -ed2 (a) -ed2 (b) = e1 (a) -ed2 (a). It will be easily understood that this provides one-way
directivity.
[0005]
However, the above primary pressure gradient microphone has only a single directional
characteristic to the front side. Therefore, in an environment where noise is emitted from all
directions (four-way) (such as an environment where noise sources can not be fixed in a specific
direction), such as a vehicle interior while driving, a factory or an airport, the purpose of a
specific direction Even if only the sound from the sound source is input, the noise can not be
blocked.
[0006]
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2
Therefore, although the present inventor is not known, as illustrated in FIG. 13, two types of
directivity with the two primary pressure gradient microphones 10-1 and 10-2 directed in
opposite directions to each other. Considered a microphone configured to have. The first
microphone 10-1 is directed to a specific target sound source, and its single directivity
characteristic picks up the sound of the target sound source and the surrounding noise. The
second microphone 10-2, directed in the opposite direction to the first microphone 10-1, will
pick up noise exclusively due to its unidirectional nature. By taking the difference between the
output of the first microphone 10-1 and the output of the second microphone 10-2, it is possible
to reduce the noise coming from all directions and obtain the target sound.
[0007]
As a result of further study of the above technology, the inventor has clarified the following
points. Firstly, it is physically impossible to arrange the two primary pressure gradient
microphones at the same position, and because of the directivity characteristics as exemplified in
FIG. It has been clarified by the inventor that it is difficult to expect high precision noise
cancellation. Second, it was clarified that in order to meet the demand for miniaturization, it is
necessary to realize a primary pressure gradient microphone having two types of directivity
characteristics using fewer than four nondirectional microphone units. The
[0008]
The present invention has been made in view of the above circumstances, and an object thereof
is to provide a primary pressure gradient microphone which is excellent in noise cancellation
effect and can obtain two types of directivity using four or less nondirectional microphone units.
To provide.
[0009]
Another object of the present invention is to provide a primary pressure gradient microphone
capable of acquiring sound from a target sound source in a specific direction with good S / N
under an environment where noise is emitted from all directions.
[0010]
The above and other objects and novel features of the present invention will become apparent
from the description of the present specification and the accompanying drawings.
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3
[0011]
SUMMARY OF THE INVENTION The best primary pressure gradient microphone according to the
present invention, as illustrated in FIG. 1, uses two nondirectional microphone units to realize
two types of directivity characteristics. First delaying means (1) for delaying the output of the
first omnidirectional microphone unit (M1, M2) and the first omnidirectional microphone unit
(M1, M2) disposed at a predetermined interval; And second delay means (2) for delaying the
output of the second nondirectional microphone unit, and the difference between the output of
the first nondirectional microphone unit and the output of the second delay means , And a
second addition means (4) for outputting the difference between the output of the second
nondirectional microphone unit and the output of the first delay means. Become.
[0012]
Assuming that the first nondirectional microphone unit (M1) is the front of the microphone, the
signal system for obtaining the output of the first addition means (3) is the two microphone units
(M1, M2). The signal system for obtaining the output of the second addition means (4) functions
as a main microphone (see FIGS. 2 and 3) having directivity characteristics on the front side, and
the two microphone units (M1). , M2) function as a reference microphone (see FIGS. 4 and 5)
having directional characteristics on the back side.
In an environment where noise is emitted from all sides and the noise source can not be
identified, the main microphone facing the target sound source picks up only the target sound
and the noise, and the reference microphone picks up the noise only.
The noise component can be canceled by calculating the difference between the output signal
component of the main microphone and the output signal component of the reference
microphone.
At this time, since the main microphone and the reference microphone are configured using
mutually identical microphone units (M1, M2), it can be considered that both microphones are
physically arranged at the same position.
In other words, the noise components picked up by both microphones can be regarded as
substantially the same. Therefore, only the target sound component can be acquired with high S /
N.
03-05-2019
4
[0013]
Substantially the same functions as described above can be realized using three nondirectional
microphone units. That is, as illustrated in FIG. 8, the third omnidirectional microphone unit (M3)
is disposed close to the second omnidirectional microphone unit, the main microphone is the
same as above, and the reference microphone is the first delay. The difference between the
output of the means (1) and the output of the third microphone unit is obtained by the second
addition means. According to this, it is possible to realize a primary pressure gradient
microphone having two types of directivity characteristics by the three nondirectional
microphone units. Although the arrangement of the main microphone and the reference
microphone can not be regarded as completely identical, they can be arranged closely without
placing a distance between the second microphone unit and the third microphone unit, so that a
good noise cancellation effect can be obtained. Can.
[0014]
Substantially the same functions as described above can be realized by using four nondirectional
microphone units. That is, as illustrated in FIG. 9, the third and fourth nondirectional microphone
units are placed at a predetermined distance in the cross direction with respect to the
arrangement direction of the first and second nondirectional microphone units (see FIG. M3 and
M4) are arranged, and the difference between the output of the delay means for delaying the
output of the second nondirectional microphone unit and the output of the first nondirectional
microphone unit is formed by the first addition means A difference between an output of the
third nondirectional microphone unit and an output of the fourth nondirectional microphone unit
is formed by a second addition unit. Although the number of microphone units is four, the main
microphone and the reference microphone can be logically regarded as being located at the
center of four radially arranged microphone units, and an excellent noise cancellation effect Can
be realized.
[0015]
Furthermore, in the case of using four nondirectional microphone units, as illustrated in FIG. 12,
the main microphone and the reference microphone configured by two nondirectional
microphone units are respectively different nondirectional It comprises by a microphone unit
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5
(M1-M4). That is, the main microphone is configured using the first and second nondirectional
microphone units (M1 and M2), and the reference microphone is configured using the third and
fourth nondirectional microphone units (M3 and M4) Do. The main microphone has directional
characteristics on the front side, and the reference microphone has directional characteristics on
the rear side. At this time, the arrangement of the third and fourth omnidirectional microphone
units is the same as the arrangement of the first and second omnidirectional microphone units,
and the first and second omnidirectional microphone units are the third. And a fourth
omnidirectional microphone unit. Therefore, the difference in the sound field between the noise
picked up by the main microphone and the noise picked up by the reference microphone is
minimized, and the target sound can be acquired with a relatively good S / N.
[0016]
The process of canceling noise using the outputs of the first and second addition means can be
performed by an analog method, but in the case of adopting a digital method, the first addition
means A first A / D converting means (5) for converting the output of the second to a digital
signal, a second A / D converting means (6) for converting the output of the second adding
means to a digital signal, It may further include digital signal processing means for canceling
noise components contained in both the output of the A / D conversion means of 1 and the
output of the second A / D conversion means.
[0017]
The digital signal processing means comprises adaptive filter means (7) receiving the output of
the second A / D conversion means (6), the output of the adaptive filter means and the output of
the first A / D conversion means And digital addition means (8) for calculating the difference
between
[0018]
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a primary
pressure gradient microphone according to the present invention.
In the microphone shown in the figure, two nondirectional microphone units M1 and M2 having
substantially the same performance are arranged at an interval of a distance d, and the output e1
of the microphone unit M1 is τ1 (τ1: The delay amount (delay amount converted to distance) is
delayed, and the output e2 of the microphone unit M2 is delayed by the delay circuit 2 by τ2
(τ2: delay amount converted to distance).
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Then, the inverting addition circuit 3 that calculates the difference between the output e1 of the
microphone unit M1 and the output ed2 of the delay circuit 2, and the difference between the
output e2 of the microphone unit M2 and the output ed1 of the delay circuit 1 An inverting
addition circuit 4 is provided. The inverting addition circuits 3 and 4 can be composed of, for
example, an operational amplifier, a feedback resistor, and an input resistor. The noninverting
input (+) is e1 and e2, and the inverting inputs (-) are ed2 and ed1.
[0019]
The microphone is stored in a casing (not shown) so that the microphone unit M1 is disposed on
the front. A ceramic type or an electret type microphone unit may be adopted as the microphone
units M1 and M2.
[0020]
At this time, the microphone has the main microphone of FIG. 2 having the signal path for
obtaining the main signal Vm from the inverting addition circuit 3 and the signal path for
obtaining the reference signal Vr from the inverting addition circuit 4. It can be grasped as two
types of primary pressure gradient microphones with a reference microphone.
[0021]
The main microphone has directivity characteristics on the front side, and has directivity
characteristics for picking up target sound and noise from the front side.
The main signal Vm is given by Vm (k, θ) = e1−ed2 = 2 · e1 · sin {k (τ2 + d · cos θ) / 2}.
[0022]
The main microphone that can be grasped as shown in FIG. 2 has directional characteristics with
respect to the front side, and has the directional characteristics illustrated in FIG. It will be
understood from the contents described qualitatively already based on FIG. 6 that such
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7
directional characteristics are obtained.
[0023]
The reference microphone has directional characteristics on the back side, does not pick up
target sound and noise from the front side, and has directional characteristics to pick up noise
from the back side. The reference signal Vr is given by Vr (k, θ) = e2−ed1 = −2 · e1 · sin {k (τ1
+ d · cos θ) / 2}. However, in the above two equations, k = 2π / λ (λ: wavelength of sound), the
characteristics of the two nondirectional microphone units M1 and M2 are substantially the
same, and the incoming sound wave is a sine wave I assume.
[0024]
The reference microphone shown in FIG. 4 has directivity characteristics to the back side as
illustrated in FIG. It will be qualitatively described based on FIG. 7 that such directional
characteristics can be obtained. That is, in FIG. 7, in order to facilitate understanding, the case of
τ1 = d and θ = 0 is taken as an example. The observation point corresponding to the delay
output ed1 (a) on the microphone unit M1 side with respect to the sound coming from the Sa
direction is apparently Ped1 (a), and the observation point corresponding to the output e2 (a) of
the microphone unit M2 is Pe2 (a) It is. The observation point according to the delay output ed1
(b) of the microphone unit M1 for the sound coming from the opposite direction Sb is apparently
Ped1 (b), and the observation point according to the output e2 (b) of the microphone unit M2 is
Pe2 ( b). As apparent from the figure, since the observation points Ped1 (a) and Pe2 (a) are at the
same position, ed1 (a) = e2 (a). Therefore, the output Vr of the reference microphone is E (k, θ) =
e2 (b) + e2 (a) -ed1 (a) -ed1 (b) = e2 (b) -ed1 (b), and One-way directivity can be obtained.
[0025]
As described above, since the main microphone and the reference microphone having different
directional characteristics are realized by using two nondirectional microphone units M1 and M2
in common, the main microphone and the reference microphone having different directional
characteristics are physically Equivalent to being placed at the same position. Thus, the
microphone of FIG. 1 will pick up the sound of different components of the same sound field. On
the other hand, when the main microphone and the reference microphone are separately
configured using two nondirectional microphone units as illustrated in FIG. 13, both
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8
microphones are physically as shown in FIG. 14. Placed in different positions. Thus, both
microphones will pick up the sound of different components of different sound fields separated
by a fixed distance. In the configuration of FIG. 13, there is an unignorable difference in the
components of the sound picked up by the microphones 10-1 and 10-2 which are disposed apart
from each other in an environment where noise is emitted from four directions. In the case of
FIG. 1, since the main microphone and the reference microphone are in completely the same
sound field, the noise components picked up by both microphones can be regarded as
substantially the same even in an environment where noise is emitted from four directions.
[0026]
FIG. 10 shows an example of a polar pattern representing directivity obtained by combining the
directivity of each of the main microphone and the reference microphone. In this example, τ2 =
d / 3, and τ1 = d. As apparent from this polar pattern, the primary pressure gradient
microphone consisting of the main microphone and the reference microphone realizes two types
of directivity characteristics of the front side and the rear side by the two microphone units M1
and M2.
[0027]
An output Vm of the inverting addition circuit 3 is converted into a digital signal Dm by an A / D
converter 5, and an output Vr of the inverting addition circuit 4 is converted into a digital signal
Dr by an A / D converter 6. The main signal data Dr output from the A / D converter 6 is supplied
to an adaptive filter 7 such as a transversal filter, and the filter output of the adaptive filter 7 and
the main signal data Dm output from the A / D converter 5 The difference is calculated by the
digital adder 8.
[0028]
The adaptive filter 7 is a filter that adaptively changes the characteristics of the input signal with
respect to changes over time. That is, the input signal Dr is multiplied by the tap coefficient, the
value thereof is added in units of plural taps, an output operation for obtaining a filter output,
and the difference between the signal from the target system to which the filter output should be
made to respond and the filter output The filter characteristic is changed in real time by
performing the tap coefficient update operation of updating the tap coefficient based on the
03-05-2019
9
error signal obtained as and sequentially rewriting the tap coefficient by the update operation.
The error signal is used as the output of the digital adder 8 at the time of training sequence
timing to determine the filter response characteristic. The training sequence timing is the timing
when the microphone units M1 and M2 do not pick up the target voice. Therefore, in the training
sequence timing, the filter response characteristic of the adaptive filter 7 is determined so as to
cancel the noise component respectively contained in the main signal data Dm and the reference
signal data Dr. The training sequence is sequentially performed at an appropriate timing in order
to follow the state in which the noise generation state of the sound field changes every moment.
[0029]
As described above, the response characteristic of the adaptive filter 7 is sequentially
determined, whereby the noise component included in the main signal Vm is canceled by the
noise component included in the reference signal Vr by the subtraction by the digital adder 8. .
The output of the digital adder 8 is converted to an analog signal by the D / A converter 9. From
the D / A converter 9, it is possible to acquire a signal mainly composed of the target voice
component. As a result of trial manufacture of the circuit of FIG. 1 having the directivity
characteristic of FIG. 10 and testing, it is compared with a conventional primary pressure
gradient microphone in which single directivity is obtained by two omnidirectional microphone
units, S / N could be improved by about 10 dB.
[0030]
The adaptive filter 7 and the digital adder 8 can be configured by a digital signal processor (DSP).
Further, a low pass filter for removing high frequency components can be disposed at a stage
prior to the A / D converters 5 and 6.
[0031]
FIG. 8 shows an example in which three nondirectional microphone units are used to construct a
primary pressure gradient microphone equivalent to the above. That is, the third nondirectional
microphone unit M3 is disposed close to the nondirectional microphone unit M2. In FIG. 8, the
reference signal Vr is generated by obtaining the difference between the output of the third
microphone unit M3 and the output of the delay circuit 1 by the inverting addition circuit 4. The
main signal Vm is generated as in FIG. In the case of this example, one nondirectional
03-05-2019
10
microphone unit M3 is required more than in FIG. Also, the main microphone and the reference
microphone will not be physically located at the exact same position. However, since the
microphone units M2 and M3 can be disposed close to each other, the microphones M2 and M3
have a noise cancellation effect superior to the configuration in which the directional
characteristics are reversed and two sets of primary pressure gradient microphones are spaced
apart as illustrated in FIG. The number of units can also be reduced by one.
[0032]
FIG. 9 shows an example in which four nondirectional microphone units are used to form a
microphone equivalent to the above. That is, four nondirectional microphone units M1 to M4 are
radially arranged on the same circumference at intervals of 90 °. The main signal Vm is the
same as the configuration of the main microphone in FIG. The reference microphone forming the
reference signal Vr is configured to obtain the difference between the microphone units M3 and
M4 by the inverting adder 4. The axes of the microphone units M3 and M4 constituting the
reference microphone are at right angles to the axes of the microphone units M1 and M2
constituting the main microphone. Therefore, its directivity is as shown in FIG. 11, and the
reference microphone does not have directivity for the target sound wave from the front.
Therefore, a microphone having two types of directivity characteristics substantially the same as
in FIG. 1 is realized. In the case of this example, two nondirectional microphone units M3 and M4
are required more than in FIG. However, since the microphone units M1 to M4 are radially
arranged at 90 ° intervals on the same circumference, it can be considered that the main
microphone and the reference microphone are physically arranged at the same position. This is
superior to the configuration in which two sets of primary pressure gradient microphones shown
in FIG.
[0033]
Furthermore, in the case of using four nondirectional microphone units, as illustrated in FIG. 12,
the main microphone and the reference microphone configured by two nondirectional
microphone units are respectively different nondirectional The microphone units M1 to M4 can
be configured. The main microphone is composed of nondirectional microphone units M1 and
M2, a delay circuit 2 and an inverting addition circuit 3. The reference microphone comprises
nondirectional microphone units M 3 and M 4, a delay circuit 1 and an inverting addition circuit
4. The main microphone has directional characteristics on the front side as illustrated in FIG. 3,
and the reference microphone has directional characteristics on the rear side as illustrated in FIG.
The primary pressure gradient microphone shown in FIG. 12 is accommodated in one casing.
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[0034]
The arrangement of the nondirectional microphone units M3 and M4 constituting the reference
microphone is the same as the arrangement of the nondirectional microphone units M1 and M2
constituting the main microphone, and the microphone units M1 and M2 are adjacent to the
microphone units M3 and M4. It is arranged. That is, the distance Ls between the axes of the
microphone units M1 and M2 in FIG. 13 and the axes of the microphone units M3 and M4 is
much smaller than that in the configuration of FIG. In this respect, it is apparent that the
microphone of FIG. 12 is different from the configuration in which two separate primary
pressure gradient microphones 10-1 and 10-2 are disposed in opposite directions to each other
as shown in FIG. Therefore, the difference in the sound field between the noise picked up by the
main microphone and the noise picked up by the reference microphone is minimized, and the
target sound can be acquired with a relatively good S / N as compared with the microphone of
FIG.
[0035]
Although the invention made by the inventors of the present invention has been specifically
described based on the embodiments, it is needless to say that the present invention is not
limited thereto, and various modifications can be made without departing from the scope of the
invention. For example, the primary pressure gradient microphone according to the present
invention can also be understood as a configuration up to the addition means such as the
inverting addition circuit. Further, the relationship between τ 1, τ 2 and d is not limited to that
of FIG.
[0036]
The present invention can be widely applied to effective application of noise cancellation to input
sound waves in an environment where noise comes from all directions, such as hands-free
telephones and voice input microphones of car navigation systems. it can.
[0037]
The effects obtained by the typical ones of the inventions disclosed in the present application will
be briefly described as follows.
03-05-2019
12
[0038]
That is, a primary pressure gradient microphone having two directional characteristics can be
realized by two or three omnidirectional microphone units.
Therefore, the cost of the primary pressure gradient microphone can be reduced, and the
microphone can be miniaturized.
[0039]
Two microphones with different directional characteristics (main microphone, see by using a
primary pressure gradient microphone by using two omnidirectional microphone units or by
arranging four omnidirectional microphone units radially Since it can be regarded as a
configuration in which the microphones) are physically arranged at the same position, in other
words, since two microphones (main microphones and reference microphones) having different
directivity characteristics can be arranged in the same sound field, excellent noise You can get a
cancellation effect.
[0040]
When three nondirectional microphone units are used, in a strict sense, it can not be regarded as
a configuration in which two microphones (main microphones and reference microphones)
having different directional characteristics are physically arranged at the same position.
However, since the second microphone unit and the third microphone unit can be disposed close
to each other without leaving a space, it is possible to obtain a noise cancellation effect superior
to the conventional one, and further, the number of nondirectional microphone units is one. The
number can be reduced.
[0041]
Also, even when two microphones (main microphone and reference microphone) having different
directivity characteristics are formed by different nondirectional microphone units, the
nondirectional microphone unit constituting the main microphone and the non-directive
microphone constituting the reference microphone are also included. By arranging the
directional microphone unit adjacently, a relatively excellent noise cancellation effect can be
obtained.
03-05-2019
13
[0042]
As described above, it is possible to realize a primary pressure gradient microphone capable of
acquiring sound from a target sound source in a specific direction with a good S / N under an
environment where noise is emitted from all directions.
[0043]
Brief description of the drawings
[0044]
12 is a circuit diagram of a primary pressure gradient microphone according to the present
invention in which two types of directivity characteristics are realized using the nondirectional
microphone units.
[0045]
2 is a configuration explanatory view of the main microphone.
[0046]
3 is an explanatory view showing the directivity characteristics of the main microphone.
[0047]
It is structure explanatory drawing of FIG. 4 reference microphone.
[0048]
5 is an explanatory view showing a directional characteristic of the reference microphone.
[0049]
6 is an explanatory view for qualitatively understanding the directivity of the main microphone.
[0050]
7 is an explanatory view for qualitatively understanding the directivity by the reference
microphone.
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14
[0051]
FIG. 83 is a circuit diagram of a primary pressure gradient microphone using the nondirectional
microphone units.
[0052]
FIG. 94 is a circuit diagram of a primary pressure gradient microphone using nondirectional
microphone units.
[0053]
10 is an explanatory view showing the overall directivity characteristics of the primary pressure
gradient microphone of FIG.
[0054]
11 is an explanatory view showing the directional characteristics of the primary pressure
gradient microphone.
[0055]
FIG. 124 is a circuit diagram of another primary pressure gradient microphone using
nondirectional microphone units.
[0056]
FIG. 13 is a schematic explanatory view of microphones in which two types of directivity
characteristics are realized by separately arranging two sets of primary pressure gradient
microphones incorporated in a casing.
[0057]
14 is an explanatory view showing the directional characteristics of the primary pressure
gradient microphone.
[0058]
Explanation of sign
[0059]
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M1, M2, M3, M4 Nondirectional microphone unit 1, 2 Delay circuit 3, 4 Inversion addition circuit
5, 6 A / D converter 7 Adaptive filter 8 Digital adder 9 D / A converter
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