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JP2007151027

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DESCRIPTION JP2007151027
The present invention makes it possible to reduce acoustic echo without causing deterioration in
sound collection characteristics such as directivity. SOLUTION: Picking signals by four
microphones 12-15 arranged equidistant from a speaker 11 are made into two pairs, and each
pair is provided with an adapter 41, 42 for correcting a path difference from the speaker to the
microphone. The acoustic echo between the speaker and the microphone is reduced by
performing phase inversion and addition in each pair in the built-in adders 51 and 52. The
adapter has an adaptive filter as a main component, and performs learning operation using the
outputs of the delay units 31 and 32 as teaching materials. The phase shifter 60 subjects the
output signal of the adder to phase shift, and the adder 70 adds them. As a result, deterioration
of the directivity of the collected signal can be suppressed, and the transmission voice can be
recorded with high quality while reducing the acoustic echo. [Selected figure] Figure 1
Loudspeaker talker
[0001]
BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a
loudspeaker communication apparatus, and more particularly to a technology for realizing a
loudspeaker communication with good sound quality by reducing acoustic echo.
[0002]
In the case of adopting an integrated sound collecting and reproducing type configuration in
which the speaker and the microphone are closely arranged in the loudspeaker communication
device, the voice of the speaker is returned to the speaker side via the speaker and the
microphone of the receiver (acoustic Echo) A phenomenon occurs in which the sound is
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reproduced from the speaker on the speech side behind the speech, and if this is noticeable, it
becomes difficult to talk.
[0003]
The cause of the generation of the acoustic echo is due to the acoustic coupling between the
speaker and the microphone, and an echo canceller is used to reduce such acoustic echo.
However, the echo canceller tends to be unstable if the acoustic echo is too large, and it is
necessary to suppress the acoustic echo to some extent in the former stage.
Therefore, reduction of the acoustic echo using the sound collection signal with a plurality of
microphones conventionally has been performed.
[0004]
For example, as shown in FIG. 3, in the technique described in Patent Document 1, the
microphones 13 and 14 are connected as a pair to the noninverting input end and the inverting
input end of the phase inverting adder 1, and the microphones 12 and 15 are connected as a
pair. It is connected to the non-inversion input end and the inversion input end of the phase
inversion adder 2 and the inversion addition is performed for each pair to make the acoustic
echo from the speaker 8 to the microphones 12 to 15 total zero. Then, the adder 4 adds the
output of the phase inversion adder 1 and the output of the phase inversion adder 2 via the delay
unit 3 to suppress the deterioration of the sound collection characteristic.
[0005]
In the technique described in Patent Document 2, as shown in FIG. 4, the signal recorded by the
microphone 12 is passed through by the phase shifter 6, and the signal recorded by the
microphone 13 is 90 degrees in phase by the phase shifter 6. Shift processing is performed, the
signal recorded by the microphone 15 is passed through by the phase shifter 7 and then phase
shift processing by 180 degrees is performed by the phase inverter 8, and the signal recorded by
the microphone 14 is processed by the phase shifter 7 After the phase shift processing of 90
degrees is performed, the phase shift processing of 180 degrees is performed by the phase
inverter 9, and the outputs of the phase shifters 6 and 9 are added by the adder 10. To reduce
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acoustic echo.
[0006]
JP-A-2000-184051 (Page 3-Page 4, Fig. 1-Fig. 2) JP-A 2000-253132 (Page 2-Page 3, Fig. 1)
[0007]
In the techniques described in Patent Documents 1 and 2 described above, the reproduced signal
from the speaker is equally picked up by a plurality of microphones, the phase of the signal is
changed, and the addition process is performed to make the acoustic echo 0. ing.
In other words, it is a technology that cancels only the signal of the sound source that is
equidistant from all the microphones.
[0008]
Thus, the problem of acoustic echo is solved if the microphone and the sound source are placed
at exactly the same distance.
However, in a real environment, especially when it comes to products, it is difficult to arrange the
distance from the speaker to each microphone at the same distance completely even if the
speaker and the microphone serving as the sound source of acoustic echo are deployed in an
integrated configuration. Because of this, such prior art can not really see much improvement in
acoustic echo suppression performance.
[0009]
Therefore, it is an object of the present invention to provide a loudspeaker that reduces the
acoustic echo and prevents the deterioration of the sound collection characteristic even in a real
environment where the distances and paths from the speakers to the microphones do not match
completely, that is, when manufactured. It is in providing a calling device.
[0010]
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The loud speaker system according to the present invention comprises a speaker (11 in FIG. 1)
for reproducing a signal sent from a remote place or the like, and a speaker / reproduction
integrated device which is closely disposed with the speaker and constitutes a surrounding
device. When 2N microphones (12 to 15 in FIG. 1) for recording voice and the recording signals
of the respective microphones are N pairs, when the acoustic echo reproduced from the speaker
is generated, the acoustic echo is generated by the microphone pair Adaptive means (22, 22, 31,
32, 41, 42, 51, 52 in FIG. 1) that operate to minimize and the phase of the output signal of the
microphone pair whose acoustic echo is minimized by the adaptive means 1 and a summing
means (70 in FIG. 1) for summing the output signals of the phase shifting means.
[0011]
Specifically, the adaptation means delays the output signal of one of the microphones of the
microphone pair (31, 32 in FIG. 1), and an acoustic echo is generated when the signal level
reproduced from the speaker is larger than a predetermined value. When an acoustic echo is
generated, the output is subtracted from the output of the delay unit when the discriminator (21,
22 in FIG. 1) which is determined to be generated and the output signal of the other microphone
of the microphone pair are input. In order to minimize the difference, an adapter (41, 42 in FIG.
1) that performs learning operation using the output of the delay unit as a teaching material and
an adder (51, 52 in FIG. 1) that performs the subtraction are included.
[0012]
Further, the adaptive unit passes an input signal from the microphone, multiplies signals at a
plurality of taps in the middle of passing by the filter coefficient for each tap, and adds and
outputs the multiplication result (FIG. 1) and an update unit (4-2 in FIG. 2) that adaptively
updates the filter coefficient of the adaptive filter unit when information of acoustic echo
generation is transmitted from the discriminator.
[0013]
The phase shifting means shifts the N input signals by a constant phase at all frequencies, and
the amount of phase shift differs by 180 / N degrees for each microphone pair.
[0014]
The present invention adopts a configuration in which an adaptive device is introduced to control
the addition result of the output signals of the symmetrically arranged microphone pairs to be 0,
so that the paths between the speaker and the microphone do not necessarily coincide
completely. Even in the real environment, it is possible to reduce the acoustic echo and not to
deteriorate the sound collection characteristic, so it is possible to provide a better speech
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communication apparatus.
[0015]
The loudspeaker communication device of the present invention introduces an adapter to solve
the point where the loudspeaker and the microphone must be perfectly matched.
An adaptively operates adaptively such that an output signal is a target signal, and an adaptive
filter is a main component.
For example, when it is desired to minimize the acoustic echo as in the present invention, the
adaptive filter is operated so that the output signal is 0 when there is an acoustic echo.
[0016]
In this case, in order to minimize the acoustic echo, the adaptive filter coefficients are updated so
that the path from the speaker to the microphone is equalized.
The update is performed by learning the signal obtained by delaying the output signal of the
paired microphones by the delay unit as a learning material based on the result of addition with
the adaptive unit in the adder.
The operation is limited by the tap length of the filter, but when the paths from the speaker to
the microphone are similar to this extent, the adapter operates effectively and achieves the
purpose even if the number of filter taps is short. be able to.
[0017]
In addition, if the output signals of the respective microphone pairs are added by the adder as it
is, the sound collection characteristics regarding the sound other than the acoustic echo, for
example, the voice of the conference participant in the audio conference device will be
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deteriorated.
Specifically, although the sound from the front of the device is picked up, it may happen that the
lateral sound is not picked up.
This does not play the role of the original audio conference device.
[0018]
Therefore, the output signal of each microphone pair having an adaptor is input to the phase
shifter. The phase shifter is a device for uniformly shifting the phase of each input signal in the
entire frequency band, and the amount of shift is determined by the number N of microphone
pairs.
[0019]
Further, by disposing the phase shifter in the subsequent stage in this way, it is possible to
reduce the phase shifter to half in comparison with the conventional method, and it is also
possible to expect a reduction in the amount of calculation. By adding the output signal of this
phase shifter by an adder (70 in FIG. 1), it is possible to suppress deterioration of performance
relating to sound collection of voice, particularly directivity characteristics, and realize reduction
of acoustic echo.
[0020]
The adapter is difficult to introduce when the number of microphones is an odd number. This is
because the acoustic echo is configured to disappear when all the signals passed through the
phase shifters are added, and in such a configuration, a plurality of filters are used to minimize
one output signal. It must be updated, and the algorithm needs to be considered. But this is not
very realistic.
[0021]
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Therefore, in the present invention, the number of microphones is 2N (N is an integer of 1 or
more), and N microphone pairs are configured. An adapter is introduced in each of the
microphone pairs to minimize acoustic echo in each of the microphone pairs in advance. By this,
even if the path between the speaker and the microphone does not match completely, the
acoustic echo can be turned off, and even when the variation occurs as in the time of
commercialization, good performance with respect to acoustic echo reduction can be obtained.
Can.
[0022]
Hereinafter, embodiments of the invention will be described in detail with reference to the
drawings. FIG. 1 shows an embodiment of a speech communication system according to the
present invention. This loud speaker communication device comprises a unit 10 for integrated
reproduction and sound collection, two discriminators 21 and 22, two delay units 31 and 32, two
adaptors 41 and 42, and three adders 51 and 52. , 70 and a phase shifter 60.
[0023]
The integrated device 10 for reproducing and collecting sound has four microphones 12 to 15 at
four corners equidistant from the speaker 11 with a speaker 11 at the center for reproducing an
audio signal transmitted from a remote place through a communication line. Is a deployed device.
In the integrated device 10 for reproducing and collecting sound, the signals recorded by the
microphones 12 to 15 are transmitted to a remote place via the communication line, but at that
time, the sound reproduced from the speaker 11 goes around to the microphones 12 to 15 The
acoustic echo signal generated by
[0024]
When sound is reproduced from the speaker 11 at a large level, it can be considered that an
acoustic echo is generated. Further, when the sound is not reproduced from the speaker 11, it is
considered that the acoustic echo is not generated.
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[0025]
However, if the level of the collected signal at the microphones 12 to 15 is greater than the level
of the reproduction signal from the speaker 11, in addition to the wraparound from the speaker
11, a speaker who is around the device speaks, and the voice is also recorded simultaneously. It
is thought that
[0026]
Therefore, the discriminator 21 compares the level of the reproduction signal from the speaker
11 with the level of the sound pickup signal at the microphones 12 and 15.
As a result, when the former is large, it is determined that an acoustic echo signal is generated
(referred to as "acoustic echo generation section"), and the adapter 41 is made to function.
Similarly, the discriminator 22 compares the level of the reproduction signal from the speaker 11
with the level of the sound pickup signal at the microphones 13 and 14. As a result, when the
former is large, it is determined as an acoustic echo generation section, and the adapter 42 is
functioned.
[0027]
The delay unit 31 delays the input signal from the microphone 12 and its output is added to the
output of the adapter 41 at the adder 51, but adds an arbitrary delay amount to enable the
operation of the adapter 41. It is a thing. Similarly, the delay 22 delays the input signal from the
microphone 13 and its output is summed with the output of the adapter 42 at the adder 52, but
any delay to enable the operation of the adapter 42. Add quantity. These delay amounts may be
small values (about 2 msec).
[0028]
The adapter 41 operates so that the input signal from the microphone 15 is canceled by the
output from the delay unit 21 and the adder 51 and is minimized at the point A which is the
output of the adder 51. Since the delay unit 31 delays the input signal from the microphone 12
as described above, the adapter 51 eventually minimizes the acoustic echo signal at the point A.
For this purpose, the adapter 51 learns the output of the delay unit 31 as a teaching material.
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[0029]
Similarly, the adapter 42 operates such that the input signal from the microphone 14 is canceled
at the output from the delay 32 and at the adder 52 and is minimized at the point B which is the
output of the adder 52. Since the delay unit 32 delays the input signal from the microphone 13
as described above, the adapter 52 eventually minimizes the acoustic echo signal at the point B.
For this purpose, the adapter 52 learns the output of the delay unit 32 as a teaching material.
[0030]
FIG. 2 shows the details of the adapter 41. The adapter 42 also has the same configuration. The
adapter 41 is composed of an adaptive filter unit 41-1 and an updating unit 41-2. The adaptive
filter unit 41-1 passes the input signal from the microphone 15, multiplies the signals at the
plurality of taps in the middle of passing by the filter coefficients for each tap, adds the
multiplication results, and outputs the result to the adder 51.
[0031]
The update unit 41-2 adaptively updates the filter coefficient of the adaptive filter unit 41-1
when the information on the acoustic echo generation interval is transmitted from the
discriminator 21. This update is performed using the LMS algorithm and learning identification
method of a general adaptive algorithm, using the signal e of point A which is the output of the
adder 51 as an input. For details of the adaptive filter update, see, for example, Toshiro Oga,
Yoshio Yamazaki, Yutaka Kanada, Acoustic system and digital processing (pp. 136-142,
Institute of Electronics, Information and Communication Engineers, Corona Co.).
[0032]
Now, assuming that the input signal to the adaptive filter unit 41-1 is x and the filter coefficient
of the adaptive filter unit is h, the update equation by the LMS algorithm in the update unit 41-2
in FIG. 2 is as follows. h̲ (t) [k] = h̲ (t-1) [k] + 2μ (e [t] x [tk]) where t represents the current
time, and k is the tap of the filter coefficient Represents Also, μ is an update coefficient, and
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0.0000001 or the like is used.
[0033]
When the filter coefficients are updated by this update equation, the signal e becomes minimum.
However, depending on the value of the signal e, the filter update may be disturbed and diverged
unless the update coefficient μ is made sufficiently small.
[0034]
Since this adaptive filter update operates only in the acoustic echo generation section, which is
obtained by the above-mentioned acoustic echo generation determination unit, the signal e here
is the amount by which the generated acoustic echo signal is output to the phase shifter 60 itself.
. That this signal e is minimized is equivalent to the acoustic echo signal being minimized.
[0035]
As described above, the acoustic echo signal is minimized by the adaptation units 41 and 42.
However, when the output signal at the point A and the output signal at the point B are simply
added in the adder 70, the general integrated speech communication apparatus Typical sound
collection characteristics are degraded. Specifically, directivity characteristics occur in the
recorded signal of the entire loudspeaker communication device, and when it is desired to pick
up voices from all directions as in the conference device, this becomes a new problem.
[0036]
Therefore, in the present embodiment, the phase shift of the output signal of point A
corresponding to the microphone 12 15 pairs using the adaptor 41 and the output signal of the
point B corresponding to the microphones 13 14 pair using the adaptor 42 Enter 60 In this
embodiment, although there are two inputs to the phase shifter 60, the phase amount is shifted
by 180/2 degrees with respect to these two signals.
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[0037]
Then, the addition of the two signals passed through the phase shifter 60 by the adder 70
realizes voice collection without creating an extreme directivity characteristic. The output y of
the adder 70 is a communication signal to a remote place, there is no acoustic echo component,
and it becomes a picked up voice with a good pick-up characteristic, and a realistic voice
conference can be realized.
[0038]
As mentioned above, although one Example of this invention was described, this invention is not
limited to this Example, It can change in the range which does not deviate from the summary.
[0039]
FIG. 1 is a block diagram showing an embodiment of a loudspeaker apparatus according to the
present invention. FIG. 1 is a block diagram showing details of an adapter in FIG. 1 a first prior
art block showing a first prior art block showing a second prior art
Explanation of sign
[0040]
10 Reproduction and sound collection integrated device 11 speaker 12-15 microphone 21, 22
discriminator 31, 32 delay device 41, 42 adaptation device 51, 52, 70 adder 60 phase shifter 411 adaptive filter unit 41-2 update unit
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