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JPH05191882

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DESCRIPTION JPH05191882
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
sound pickup apparatus for adaptive noise canceller, and is applicable to, for example, an
adaptive noise canceller in a hands-free car telephone.
[0002]
2. Description of the Related Art For example, in a hands-free car telephone, a microphone having
a wide directivity is applied to increase the freedom of position of the speaker. Therefore, the
microphone captures not only the sound from the speaker (concept including voice) but also the
operating noise of the air conditioner and engine and the traveling noise from the road surface,
that is, the background noise. This degrades the call quality. Therefore, in the hands-free car
telephone, conventionally, an adaptive noise canceller that removes such background noise is
applied.
[0003]
Reference 1 "Joseph C. Liberti, Theodore S. Rappaport, and John G. Proakis," EVALUATION OF
SEVERAL ADAPTIVE ALGORITHMS FOR CANCELING ACOUSTIC NOISE INMOBILE RADIO
ENVIRONMENTS ", CH 2944-7 / 91/0000/0126, 1991 IEEE, pp 126-132 FIG. 2 shows the twomicrophone type adaptive noise canceller described in Document 1. In FIG. 2, this adaptive noise
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canceller 1 comprises a main microphone 10, a noise reference microphone 11, two analog /
digital conversion circuits 12 and 13, a delay means 14, an adaptive filter 15, a subtractor 16,
and a digital / analog conversion circuit 17 It consists of
[0004]
An acoustic signal captured by the main microphone 10 and converted into an electrical signal
(hereinafter referred to as a main acoustic signal) is converted into a digital signal by the digital /
analog conversion circuit 12 and, further, through the delay means 14, for example, an adaptive
filter After being delayed by a time corresponding to the fifteen middle taps, it is given to the
subtractor 16 as a subtractive input.
[0005]
On the other hand, an acoustic signal captured by the noise reference microphone 11 and
converted into an electrical signal (hereinafter referred to as a sub-acoustic signal) is converted
into a digital signal by the digital / analog conversion circuit 13 and is converted to, for example,
an adaptive filter 15 of FIR type. Given.
The adaptive filter 15 forms a noise component in the main acoustic signal from the input subacoustic signal and supplies it to the subtractor 16 as a subtractive input.
[0006]
Thus, the subtractor 16 obtains an acoustic signal obtained by removing the noise component
contained therein from the main acoustic signal, which is converted to an analog signal through
the digital / analog conversion circuit 17 and output.
[0007]
The above operation is performed when an acoustic signal from the speaker is given, and at this
time, the tap coefficient of the adaptive filter 15 is fixed.
The tap coefficient of the adaptive filter 15 is determined by the removal residual signal output
from the subtractor 16 in a state where there is no acoustic signal from the speaker and both the
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main microphone 10 and the noise reference microphone 11 capture background noise. It is
updated adaptively.
[0008]
FIG. 3 is a schematic perspective view showing the arrangement of the main microphone 10 and
the noise reference microphone 11. The main microphone 10 and the noise reference
microphone 11 are provided as close as possible, with the respective sound capturing surfaces
10F and 11F located on the same plane.
[0009]
In the adaptive noise canceller 1, the main microphone 10 and the noise reference microphone
11 are arranged as shown in FIG. 3 because the main microphone 10 captures the auxiliary
sound signal obtained by capturing the noise reference microphone 11. Since the noise
component contained in the main acoustic signal is formed, the noise component in the main
acoustic signal and the noise component in the auxiliary acoustic signal must have high
correlation.
[0010]
Document 1 defines a coherence function γ (ω) shown in the following equation (1) as a
representation of this correlation.
γ (ω) = Spr (ω) / (Spp (ω) Srr (ω)) 1/2 (1) where Spr (ω) is the input acoustic signal of the
main microphone 10 and the input of the noise reference microphone 11 Spp (ω) and Srr (ω)
are power spectral densities of the input acoustic signal of the main microphone 10 and the
input acoustic signal of the noise reference microphone 11, respectively. Also, ω means an
angular frequency component.
[0011]
Document 1 also describes that the expected value ψ (ω) of noise cancellation (noise elimination
amount) is given by the function of frequency ω by the following equation (2) using this
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coherence function γ (ω) doing. ψ (ω) = 1 / (1− | γ (ω) | 2) (2) When evaluated by the
equations (1) and (2) described above, practically, some kind of ultra-low from the noise source It
has been reported that the frequency signal shows high correlation even when the main
microphone 10 and the noise reference microphone 11 are separated by 20 cm or more, and
that the noise can be sufficiently canceled. On the other hand, it has been reported that even if
the distance from the main microphone 10 and the noise reference microphone 11 is about
several centimeters, the signal from the high frequency noise source has a very small correlation
and the noise can not be canceled appropriately.
[0012]
As described above, in the two-microphone type adaptive noise canceller 1, as the distance
between the two microphones 10 and 11 is made closer, the amount of noise cancellation
increases and the frequency at which the noise can be canceled is also high. It is stated that it
extends to the area.
[0013]
However, as shown in FIG. 3, in the method of placing the sound capturing surfaces 10F and 11F
of the microphones 10 and 11 on the same plane and placing the microphones 10 and 11 close
to each other, the physical properties of the microphones 10 and 11 themselves are There is a
limit to the distance that can be approached due to the size.
As a result, there is a limit to increasing the correlation of the acoustic signals captured by both
microphones 10 and 11, and there is also a limit to the frequency at which noise can be
eliminated.
[0014]
In the case of the above-described adaptive noise canceller 1 for hands-free car telephones, the
sound band of the car telephones can not be covered in practice. For example, wind noise caused
by driving a car, running noise from a road, and rotational noise of an air conditioner fan also
contain high frequency components, and such background noise is sufficiently large from the
acoustic signal from the speaker. Could not cancel.
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[0015]
Such a problem occurs not only in the case of one noise reference microphone but also in the
case of two or more noise reference microphones. Of course, as the number of microphones for
noise reference increases, the accuracy of noise cancellation is improved, but the noise can not
be canceled for high frequency components with low correlation, as described above.
[0016]
The present invention has been made in consideration of the above points, and an object of the
present invention is to provide a sound collection device for an adaptive noise canceller that can
widen a band in which noise can be canceled compared to the prior art.
[0017]
SUMMARY OF THE INVENTION In order to solve the above problems, a sound collection
apparatus for an adaptive noise canceller according to the present invention comprises a main
sound capturing means for capturing sound, and one or more noise reference sound capturing
means for capturing sound. And adaptive filter means corresponding to each noise reference
acoustic capture means for extracting noise components from the acoustic signal outputted from
each noise reference acoustic capture means; and each adaptive signal from the acoustic signal
outputted from the main acoustic capture means An adaptive noise canceller including
subtraction means for subtracting a noise component output from the filter means to obtain a
noise-canceled acoustic signal, wherein the sound capture surface of the main sound capture
means and the sound of each noise reference sound capture means A total of N sound capture
planes with the capture plane, at intervals of 360 / N degrees in the circumferential direction
around a certain point, and with respect to the above one point Characterized in that is arranged
in proximity to face a Shii distance.
[0018]
Here, it is preferable that the main sound capturing means and the noise referring sound
capturing means be mounted in the same casing having the sound intake holes to realize the
above arrangement.
[0019]
The subtraction means subtracts the noise component obtained by processing the sound signal
from the sound acquisition means for noise reference corresponding to each adaptive filter
means from the sound signal outputted from the main sound acquisition means to cancel the
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noise. In the adaptive noise canceller that outputs the acoustic signal, it is premised that the
correlation between the acoustic signal from the main acoustic capture means and the acoustic
signal from each noise reference acoustic capture means is high.
[0020]
In the present invention, in order to enhance the correlation between the acoustic signal from the
main acoustic capture means and the acoustic signal from each noise reference acoustic capture
means, the acoustic signals from the equivalent identical point sources are It was intended to
create a state equivalent to the main acoustic capture means at a distance and the noise
reference acoustic capture means for capturing.
[0021]
Therefore, a total of N sound capture planes between the sound capture plane of the main sound
capture means and the sound capture planes of each noise reference sound capture means are
spaced 360 / N degrees circumferentially around a certain point In addition, they were arranged
close to one another with an equal distance to one point.
[0022]
There are various configurations for supporting such main sound capturing means and each
noise reference sound capturing means for realizing the arrangement of a plurality of sound
capturing planes, but the relative positional accuracy and productivity of the plurality of sound
capturing planes, etc. In consideration of the above, it is preferable to realize the main sound
capturing means and the noise referring sound capturing means in the same casing having the
sound intake holes.
[0023]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a sound
collecting apparatus in which the noise reference microphone is applied to one adaptive noise
canceller will be described in detail with reference to the drawings.
The electrical configuration of the adaptive noise canceller to which this embodiment is applied
has the configuration shown in FIG. 2 described above as in the prior art, and therefore the
description thereof is omitted.
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[0024]
FIG. 1 is a perspective view showing the configuration of the sound collecting apparatus of this
embodiment, and the same reference numerals are given to the same corresponding parts as FIG.
FIG. 4 is a longitudinal sectional view of the casing in the first embodiment.
[0025]
In FIG. 1, the main microphone 10 and the noise reference microphone 11 of this embodiment
are mounted and mounted in the same casing 20.
[0026]
In the case of this embodiment, one having the same cylindrical shape is applied as the main
microphone 10 and the noise reference microphone 11.
Therefore, the casing 20 in which the microphones 10 and 11 are mounted and accommodated
has a cylindrical shape whose both end surfaces are open, and the inner peripheral surface
thereof substantially coincides with the outer peripheral surfaces of both the microphones 10
and 11.
[0027]
The inner peripheral diameter of the longitudinal central portion of the casing 20 is slightly
smaller than the inner peripheral diameter on both end sides, whereby, as shown in FIG. 4, step
portions 21a and 21b are formed on the inner peripheral surface. There is.
The main microphone 10 and the noise reference microphone 11 are inserted into the casing 20
from the side of the sound capturing surfaces 10F and 11F, and are inserted and mounted so as
to be in contact with the above-described step 21a or 21b.
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In such a wearing state, the sound capturing surfaces 10F and 11F of the two microphones 10
and 11 face each other.
In practice, the steps 21a and 21b are provided such that the distance between the sound
capturing surfaces 10F and 11F is about several mm.
[0028]
A space formed by both the sound capturing surfaces 10F and 11F and the inner peripheral
surface of the casing 20 is a casing by a plurality of elongated holes (hereinafter referred to as
acoustic intake holes) 22 drilled in the central portion of the casing 20. It is in communication
with 20 external spaces.
That is, sounds generated outside the casing 20 are taken into the casing 20 by the sound intake
holes 22 and reach the sound capturing surfaces 10 F and 11 F of the two microphones 10 and
11.
[0029]
As described above, since the sound generated outside the casing 20 is taken into the casing 20
through the sound intake hole 22 and reaches the sound capturing surfaces 10F and 11F, the
sound source position and the frequency of the sound signal Regardless, it can be captured in the
space formed by both sound capturing surfaces 10F and 11F and the inner circumferential
surface of the casing 20 (considered as a point space).
That is, conventionally, both microphones 10 and 11 could not be brought close to their physical
size or more (the limit of about 1 to 2 cm), but in the case of this embodiment, they can be
brought to about several mm, Moreover, the captured acoustic signal can be made substantially
the same over the entire frequency component.
[0030]
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Therefore, the acoustic signals output from both the microphones 10 and 11 are highly
correlated, and it is possible to perform good noise cancellation over the entire necessary band.
[0031]
FIG. 5 shows the noise cancellation characteristic when the sound collection device for adaptive
noise canceller according to this embodiment (FIG. 1) is applied, and FIG. 6 shows the sound
collection device for adaptive noise canceller according to the prior art (see FIG. 3). It shows the
noise cancellation characteristic when applied.
In FIGS. 5 and 6, curves AIN1 and AIN2 are respectively the power spectrum of noise (car air
conditioner fan noise) captured by the main microphone 10, and curves AOUT1 and AOUT2 are
output signals from the corresponding adaptive noise canceller, respectively. Power spectrum of
Therefore, the portion where the input noise curve AIN1 or AIN2 and the output noise curve
AOUT1 or AOUT2 overlap means a band in which noise cancellation can not be realized.
[0032]
As apparent from the comparison of FIGS. 5 and 6, in the case of this embodiment, good noise
cancellation can be realized over almost the entire acoustic band (300 Hz to 3 kHz) of the car
telephone unlike the prior art. I understand that
[0033]
FIG. 7 shows a cross-sectional view of a casing 30 according to a sound collecting apparatus of a
second embodiment of the present invention.
This is a cross-sectional view in the same direction as FIG.
[0034]
This second embodiment is directed to an adaptive noise canceller having two microphones 11A
and 11B as noise reference microphones. That is, although illustration is omitted, the noise
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component formed based on the sub acoustic signal from one of the noise reference
microphones 11A is removed from the main acoustic signal from the main microphone 10, and
from the acoustic signal after the removal, The present invention is directed to an adaptive noise
canceller that removes noise components formed based on the auxiliary sound signal from the
other noise reference microphone 11B.
[0035]
In FIG. 7, the casing 30 to which the main microphone 10 and the two noise reference
microphones 11A and 11B are attached has cylindrical portions 31, 32 and 33 into which the
respective microphones 10, 11A and 11B are inserted, and these cylindrical portions 31 and A
central portion 34 is formed to connect the ends 32 and 33 together.
[0036]
The cylindrical portions 31, 32 and 33 are provided such that their center lines intersect at one
point P and at an angle of 120 degrees.
In addition, protrusions 35, 36, 37 having a very small amount of protrusion are provided on the
inner peripheral surfaces of the end portions on the central portion 34 side of the cylindrical
portions 31, 32, 33, respectively. The positions of the microphones 10, 11A, and 11B are
determined by the reference numeral 37, and the relative positional relationship between the
sound capturing surfaces 10F, 11AF, and 11BF is defined. That is, the sound capturing surfaces
10F, 11AF, and 11BF are positioned close to each other at intervals of 120 degrees in the
circumferential direction around the point P and at equal distances to the point P.
[0037]
Also in this second embodiment, the sound intake hole is formed so that the sound generated
outside the casing 30 can be taken into the space formed by the sound capturing surfaces 10F,
11AF and 11BF and the inner surface of the central portion 34. 38 are provided.
[0038]
Therefore, according to the second embodiment as well, the sound generated outside the casing
30 is taken into the casing 30 through the sound inlet 38 and reaches the sound capturing
surfaces 10F, 11AF and 11BF. Regardless of the position or frequency of the acoustic signal, it
can be captured in the space (considered as a point space) formed by the acoustic capture
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surfaces 10F, 11AF and 11BF and the inner surface of the casing 30, and the acoustic capture of
each microphone 10, 11A, 11B The faces 10F, 11AF and 11BF can be brought closer than the
physical size of the microphone, and the captured acoustic signal can be approximately the same.
[0039]
Therefore, the acoustic signals output from the respective microphones 10, 11A, 11B are highly
correlated, and it is possible to perform good noise cancellation over the entire necessary band.
[0040]
In the above embodiment, although the case where the noise reference microphones are one or
two is shown, the present invention can be applied to the case where the noise reference
microphones are three or more.
[0041]
Furthermore, although the present invention is suitable for application to an adaptive noise
canceller for hands-free car phones having a lot of high frequency noises, it is of course widely
applicable to adaptive noise cancellers other than this application.
[0042]
Furthermore, the acoustic intake holes 22 and 38 provided in the casing of the above
embodiment may be acoustic holes, and it is not a requirement that they be complete through
holes.
For example, it may be a sound intake which is clothed to prevent dust and dirt from entering the
casing.
[0043]
Furthermore, the present invention is characterized by the relative positional relationship of the
sound capturing surfaces of the plurality of microphones, and if the relative positional
relationship of the sound capturing surfaces similar to the embodiment can be realized, a
plurality of microphones can be realized. The supporting structure of the microphones of this
embodiment may be different from the above embodiment.
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[0044]
As described above, according to the present invention, there are a total of N acoustic capture
planes consisting of the acoustic capture plane of the main acoustic capture means and the
acoustic capture planes of each noise reference acoustic capture means, Because it is arranged
closely in the circumferential direction centering on at intervals of 360 / N degrees and with
equal distance to a certain point, the noise cancelable band can be wider than before A noise
canceller sound pickup device can be realized.
[0045]
Brief description of the drawings
[0046]
1 is a perspective view showing a sound collection device for an adaptive noise canceller of the
first embodiment.
[0047]
2 is a block diagram showing an electrical configuration of the adaptive noise canceller.
[0048]
3 is an explanatory view of a conventional microphone mounting method.
[0049]
4 is a cross-sectional view of the microphone mounting casing of the first embodiment.
[0050]
5 is a characteristic curve diagram (part 1) for explaining the effect of the first embodiment.
[0051]
6 is a characteristic curve diagram (part 2) for explaining the effect of the first embodiment.
[0052]
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7 is a cross-sectional view of the microphone mounting casing of the second embodiment.
[0053]
Explanation of sign
[0054]
10: main microphone (main sound capturing means), 10F: sound capturing surface of main
microphone, 11: microphone for noise reference (sound capturing means for noise reference),
11F: sound capturing surface of microphone for noise reference, 20: casing, 22 ... sound intake
hole.
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