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JP2000184051

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DESCRIPTION JP2000184051
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
audio conference apparatus provided with a microphone and a speaker, and a sound collection
method.
[0002]
2. Description of the Related Art An example of a conventional audio conference apparatus
equipped with a microphone and a speaker is shown in FIG.
[0003]
As shown in FIG. 3, the microphones A− and B− are connected to the inverting input terminal of
the phase inverting adder 1.
The microphones C + and D + are connected to the noninverting input terminal of the phase
inverting adder 1. An output signal from the phase inversion adder 1 is supplied to the
transmission / reception circuit 5 and is output from the transmission / reception circuit 5 as a
transmission signal 6 to a telephone line or a dedicated line (not shown). Further, a reception
signal 7 from a telephone line or a dedicated line (not shown) is supplied to the speaker 8
through the transmission / reception circuit 5. Further, as shown in FIG. 4, the microphone A− is
disposed to face the microphone C + centering on the speaker 8, and the microphone B− is
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disposed to face the microphone D + centering on the speaker 8.
[0004]
By the way, in the above-mentioned conventional audio conference apparatus, since they are
arranged as shown in FIG. 4, audio from the directions of 90 degrees and 270 degrees is input in
the same phase. As a result, there is a problem that the phase inversion adder 1 cancels out, and
the sound collection sensitivity in the directions of 90 degrees and 270 degrees is lowered as
shown in "combined microphone directivity characteristic" of FIG. .
[0005]
Further, as shown in FIG. 3, the signal 9 to be circulated by the acoustic coupling from the
speaker 8 is captured in the same phase into the microphones A-, B-, C + and D +, which causes a
problem of howling and noise.
[0006]
Incidentally, in the technique disclosed in Japanese Patent Application Laid-Open No. 64-29154,
howling is prevented by the echo cancellation circuit, but a training signal is used to cancel the
loop signal by the echo cancellation circuit. Since it is necessary to set the parameters of the echo
cancellation circuit, there is a problem that the setting operation of the parameters becomes
complicated.
[0007]
The present invention has been made to solve such conventional problems, and it is an object of
the present invention to provide an audio conference apparatus and a sound collection method
that can reduce acoustic coupling and improve sound collection characteristics. Do.
[0008]
SUMMARY OF THE INVENTION In order to achieve the above object, according to a first aspect
of the present invention, there is provided an audio conference apparatus having a speaker and a
center of the speaker as a symmetry center, at a distance L from the symmetry center. First and
second microphones disposed at two points symmetrical with respect to the center of symmetry,
and a third microphone disposed at a distance L from the center of symmetry and at the other
two points symmetrical with respect to the center of symmetry And fourth microphone, first
addition means for adding the signal from the first microphone and the signal from the second
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microphone, the signal from the third microphone and the fourth microphone , And delay means
for delaying the signal from the second addition means by a predetermined time, and the signal
from the delay means and the signal from the first addition means to add 3 of the adding means,
and a city.
[0009]
In this case, the first addition means is a phase inversion adder that inverts and adds the phase of
the signal from the first microphone or the second microphone, and the second addition means is
the first addition means It can be configured by a phase inverting adder that inverts and adds the
phase of the signal from the third microphone or the fourth microphone.
[0010]
Further, the third adding means can be configured to be supplied to the communication line via
the transmitting and receiving circuit.
Further, the signal received from the communication line can be supplied to the speaker via the
transmission / reception circuit.
[0011]
In the sound collection method according to the second aspect of the present invention, for the
same purpose as above, the center of the speaker is the symmetry center, the distance L from the
symmetry center, and two first points symmetrical about the symmetry center. And a second step
of arranging the third microphone and the second microphone, and arranging a third
microphone and a fourth microphone at another two points symmetrical to the center of
symmetry at a distance L from the center of symmetry A third step of adding a signal from the
first microphone and a signal from the second microphone; and adding a signal from the third
microphone and a signal from the fourth microphone The fourth step, the fifth step of delaying
the signal added in the fourth step by a predetermined time, and the signal delayed in the fifth
step and the signal added in the third step And a sixth step of adding.
[0012]
In this case, in the third step, the phases of the signals from the first microphone or the second
microphone are inverted and added, and in the fourth step, the third microphone or the fourth
microphone Can be configured to invert and add the phase of the signal from.
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[0013]
Further, it may be configured to further include the step of sending out the signal generated by
the addition in the sixth step to the communication line via the transmission / reception circuit.
Further, the method may further include the step of supplying the signal taken from the
communication line to the speaker via the transmission / reception circuit.
[0014]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A voice conference apparatus
according to the present invention will be described in detail with reference to the accompanying
drawings.
In the drawings described below, the same reference numerals as in FIG. 3 denote the same parts.
[0015]
FIG. 1 is a block diagram showing the configuration of the audio conference apparatus according
to the embodiment of the present invention, and FIG. 2 is a diagram for explaining the operation
of the audio conference apparatus shown in FIG.
[0016]
In FIG. 1, the audio conference apparatus includes microphones A−, A +, B− and B +, phase
inversion adders 1 and 2, a delay unit 3, an adder 4, a transmission / reception circuit 5 and a
speaker 8.
[0017]
As shown in FIG. 2, the microphones A− and A + are located at two points symmetrical to each
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other with the center of the speaker 8 as the center of symmetry, the distance L from the center
of symmetry, and the centers of symmetry.
Also, the microphones B− and B + are located at the other two points that are at a distance L
from the center of symmetry and are symmetrical with respect to the center of symmetry.
[0018]
The microphone A− is connected to the inverting input terminal of the phase inverting adder 1.
The microphone A + is connected to the noninverting input terminal of the phase inverting adder
1.
The output of the phase inversion adder 1 is supplied to the adder 4.
[0019]
The microphone B− is connected to the inverting input terminal of the phase inverting adder 2.
The microphone B + is connected to the noninverting input terminal of the phase inverting adder
2.
The output of the phase inversion adder 2 is supplied to the adder 4 via the delay unit 3.
[0020]
The output of the adder 4 is output as a transmission signal 6 via a transmission / reception
circuit 5 to a telephone line or a dedicated line (not shown).
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A received signal 7 from a telephone line or a dedicated line (not shown) is supplied to the
speaker 8 through the transmission / reception circuit 5.
[0021]
Next, the sound collection method in the audio conference apparatus configured as described
above will be described.
[0022]
First, an audio signal generated by collecting the sound by the microphones A− and A + is
supplied to the adder 4 through the phase inverting adder 1.
Further, an audio signal generated by collecting the sound by the microphones B− and B + is
supplied to the adder 4 via the phase inverting adder 2 and the delay unit 3.
[0023]
Here, as shown in FIG. 2, the microphones A− and A + are located at two points symmetrical to
each other with the center of the speaker 8 as the center of symmetry and at a distance L from
the center of symmetry. -And B + are located at a distance L from the center of symmetry and are
arranged at other two points symmetrical with respect to the center of symmetry. Therefore, the
loop signals 9 from the speaker 8 to the microphones A-, A +, B- and B + are all input to the phase
inverting adders 1 and 2 in the same phase. Thereby, the in-phase detour signal 9 is canceled in
each of the phase inverting adders 1 and 2.
[0024]
Further, among the signals input to the adder 4, the audio signals from the microphones B− and
B + are delayed from the audio signals from the microphones A− and A + by a predetermined
time. Therefore, in the adder 4, the sound signals from the microphones A− and A + and the
sound signals from the microphones B− and B + are added without being canceled, so that the
sound collection sensitivities in the directions of 90 degrees and 270 degrees are good.
Maintained.
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[0025]
Here, the delay amount of the delay unit 3 is a small amount, and is selected so as not to affect
the frequency characteristic of the microphone sound collection as a voice call. The amount of
delay by the delay device 3 is preferably, for example, about 875 μsec.
[0026]
As described above, in the audio conference apparatus according to the present embodiment, the
audio signals from the microphones A− and A + are added by the phase inverting adder 1, and
the audio signals from the microphones B− and B + are phase inverted adders. Since the addition
is performed by 2, the invert signal 9 input in the same phase can be canceled by each of the
phase inverting adders 1 and 2, and acoustic coupling can be reduced.
[0027]
Further, when adding the audio signals by the adder 4, the audio signals from the microphones
B- and B + are delayed by the delay unit 3 for a predetermined time, so that the audio signals
from the microphones A- and A + and the microphones B- and B + Since the sound signals from
the above are added without being offset, the sound collection sensitivities in the directions of 90
degrees and 270 degrees can be maintained well, and the microphone directivity characteristic of
all-surround sound collection can be realized.
[0028]
As described above in detail, according to the present invention, it is possible to provide an audio
conference apparatus and a sound collection method capable of reducing acoustic coupling and
improving sound collection characteristics.
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