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DESCRIPTION JPS62250760

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DESCRIPTION JPS62250760
[0001]
The present invention relates to a call system, and more particularly to preventing howling in a
simultaneous call system using a microphone and a speaker. As shown in FIG. 1, in a speech
system using a transmitting microphone such as a speakerphone and an interphone and a
receiving speaker, in general, the transmitting microphone and the receiving speaker are
operated simultaneously at the same time between the microphone and the speaker. A loop
circuit is formed by the acoustic coupling of the two, and howling occurs at a frequency at which
the gain exceeds 1 in relation to the magnitude of looping. That is, in FIG. 2, OA indicates the
transmission path of the speaker A, and includes the transmission microphone MA of the speaker
A11ll, the amplifier 1, and the reception speaker SB on the speaker B side. OB indicates a
transmission route of the speaker B, and includes a transmission microphone MB for the speaker
B, 7 amplifiers 2 and a reception speaker SA for the speaker A. In this case, the two transmission
paths OA and OB are loop-connected to form a loop circuit by the acoustic coupling of the
speaker SA-microphone MA and the speaker SB-microphone MB. In the conventional
communication system, as a measure for preventing howling, when one transmission path is in
operation, a measure is taken to limit the transmission gain so that the other transmission path is
likely to be cut off. That is, in FIG. 2, when transmitting to the speaker, the transmitting
microphone MA is activated, and at the same time the input signal to the receiving speaker SA is
blocked or the input signal level is restricted to form a loop circuit. However, a so-called pushpull talk system is generally adopted, in which the loop gain is set to less than 1 to prevent
howling. However, in this method, since both the speakers A and B can not simultaneously make
simultaneous loud-speaking calls, there is a risk of causing problems such as failure to smoothly
communicate with the interlocutors. SUMMARY OF THE INVENTION The present invention
solves the above-mentioned drawbacks of the prior art, and provides a speech system capable of
simultaneous simultaneous loud-speaking of both speakers and greatly improving the howling
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margin. (Summary of the Invention) In the present invention, a transmitting microphone and a DI
microphone close to this are provided, and the output signal of the secondary microphone
obtained by the proximity sound source present in localized values close to both microphones is
A correction is made to match the magnitude and phase with that of the output signal from the
same sound source of the transmitting microphone, and using this correction signal, only the
signal component by the same sound source contained in the output signal of the transmitting
microphone is canceled. Therefore, by using a directional microphone device having a
characteristic that lowers the sensitivity to the same sound source and arranges a speaker for
reception at the position where the above-mentioned near sound source exists, the acoustics of
the microphone for transmission and the speaker for reception are arranged. Howling of the twoway loud simultaneous communication system is prevented by sufficiently reducing the degree of
coupling.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment) Prior to the
description of the embodiment, a directional microphone device which is a basic configuration of
the present invention described in the section "Summary of the invention" will be briefly
described. As to this directional microphone device, as already described by the present applicant
and described in detail in Japanese Patent Application No. 61-30692, under the situation where
ambient noise already exists before this microphone device, Microphones with sharp directivity
characteristics such as superdirectivity have been put to practical use in order to pick up the
target sound clearly, but with these directional microphones, good results are obtained for
distant sound sources (more than 1 + ua) Although it can be obtained, proximity noise is affected
by the proximity effect unique to the microphone, and the directivity characteristic becomes
different from that of the distant sound source, and sensitivity to proximity noise will be
obtained. Compared with the output level of the microphone by the sound source, it has the
disadvantage that it is picked up at an output level of an unnoticeable magnitude. Therefore, as
shown in FIG. 3, this directional microphone device comprises a main microphone M
corresponding to a sound source for sound collection and a sub microphone M2 provided in the
vicinity of the main microphone M; A correction circuit 1 having a transmission interval WL't o to
correct the signal level and phase of the output signal of the microphone M2, an output signal of
the main microphone M, and an output signal of the sub microphone obtained through the 111
positive circuit 1 The output signal component of the main microphone M1 obtained by the noise
source adjacent to the main and λ IJ microphones is composed of the arithmetic circuit 2
(subtracting circuit in the figure) adding or subtracting Signal level and phase of the output
signal component from the law microphone M2 in the correction circuit 2 in order to eliminate
the cancellation using the output signal component of By correcting the characteristic to match
that of the output signal component of the main microphone M1 (in this case, the polarity of
both signal components may be the same because a subtraction circuit is used), the sensitivity to
the proximity noise source is significantly reduced. The In the two-way loud simultaneous voice
communication system according to the present invention, using the above directional
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microphone device, the main microphone is used as a transmitting microphone, the receiving
speaker is arranged at the position where the proximity noise source exists, and the output from
the receiving speaker The output signal component of the secondary microphone obtained by
voice matches the output signal component of the transmitting microphone obtained by the same
output voice with the signal level and phase characteristics, and is added or subtracted from the
output signal of the main microphone. The output signal component due to the same output
voice contained in the output signal of the microphone is canceled to substantially weaken the
acoustic coupling between the transmitting microphone and the receiving speaker.
Hereinafter, the present invention will be described in detail based on the illustrated
embodiments. FIG. 1 shows the basic configuration of one speaker side of the two-way loud
simultaneous voice communication system according to the present invention, and 11 is a main
microphone for transmission, the direction of maximum sensitivity of which is directed
substantially to the direction of the speaker To. 12 is an IHIJ microphone, and SP is a receiver.
The reception speaker SP is disposed at a position (within 1 + o from the reception speaker SP to
both microphones respectively) W1 in close proximity to the main + ii microphones. A correction
circuit 13 has a transfer function Y0 to correct the amplitude characteristic and the phase
characteristic of the output signal from the ill microphone. The role of the correction circuit 13 is
to match the amplitude characteristic and the phase characteristic of the output signal obtained
from the a re-microphone 12 with that of the output signal component of the main microphone
11 obtained by the output sound from the receiving speaker SP. That is, with regard to the
output signals of the main and sub microphones obtained by the output voice from the receiver
speaker SP, the amplitude characteristics are the difference in the distance between each
microphone 711.12 and the receiver speaker SP, the microphones 11. The characteristics differ
depending on the directivity characteristics, proximity effect and sensitivity differences of 12 and
the phase characteristics are the arrival times of the output voice to each microphone 11.12
caused by the difference in distance between each microphone 11.12 and the reception speaker
Each differs depending on the difference in Therefore, in order to offset the output signal
component obtained by the above-mentioned output voice contained in the output signal of the
main microphone by the output signal of the sub microphone, it is necessary to eliminate 3 + A
and match each characteristic. Therefore, in the present invention, the correction circuit 13
corrects the output signal of the microphone 11. Denoted at 14 is a subtraction circuit which
eliminates the output signal from the sub microphone 12 which has passed through the
correction circuit 13 from the output signal of the main microphone 11. As a result, the output
signal component of the main microphone obtained by the output sound from the reception
speaker SP is canceled out. In the above case, the output signal component of the main
microphone obtained by the output sound from the reception speaker SP and the output signal of
the sub microphone by the same output sound obtained through the correction circuit 13 have
been described. If the output signal has a different polarity, an adder circuit is used. The
correction characteristics of the correction circuit 13 are designed so that the output signals of
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the main and primary microphones match only when the receiver speaker SP is in the positional
relationship shown in FIG. At positions other than the fixed position of the speaker SP, for
example, for voice from a speaker, an output signal substantially determined by the sensitivity of
only the main microphone is obtained, and is output to the other speaker via the amplifier 15.
According to this communication system, the sensitivity to the output voice from the speaker for
reception may be lowered by about 20 to 25 dB in the entire communication band as compared
with the microphone sensitivity in the direction of the speaker regardless of the directivity
characteristics of the main and u11 two microphones. Since it is possible, the reproduction level
of the reception speaker can be increased by about 10 to 15 dB as compared with the case of
using only the conventional directional microphone which causes the sensitivity increase due to
the proximity effect, and a clearer two-way simultaneous call becomes possible. In the above
embodiment, although the main and sub microphones and the receiving speaker are arranged
substantially on a straight line, the present invention is not limited to this. The maximum
sensitivity of each of the main and sub microphones is within the range where correction by the
correction circuit is possible. It is possible to arbitrarily set the direction, the distance difference
between the main and sub microphones, the position of the receiving speaker, and the like.
(Effects of the Invention) In the present invention, the transmitting microphone and the auxiliary
microphone close to this are provided, and the output signal of the auxiliary microphone
obtained by the proximity sound source present at a fixed position close to both microphones is
A correction is made to match the magnitude and phase with that of the output signal from the
same sound source of the transmitting microphone, and this correction signal is used to cancel
only the output signal component from the same sound source contained in the output signal of
the transmitting microphone. Since the receiver for speech reception is arranged at the position
where the above-mentioned proximity sound source exists using the directional microphone
device as described above, and the sensitivity to the output sound from the speaker for reception
is simply reduced, it is possible to transmit substantially The degree of acoustic coupling between
the microphone and the receiving speaker is sufficiently small! It is possible to significantly
improve the howling margin in the two-way loud simultaneous communication system.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a block diagram showing a basic configuration of the simultaneous speech
communication system according to the present invention, FIG. 1 is a block diagram showing a
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conventional communication system, and FIG. 3 is a basic configuration of a directional
microphone device used in the present invention. FIG.
REFERENCE NUMERALS 11 ... ... main microphone 12 ...... sub microphone 13 ...... correction
circuit 14 ...... subtraction circuit SP ...... receiver speaker Patent Name of applicant Aiwa Co., Ltd.
Fig. 1 A Fudan
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