JPH01320846A - Microphone speaker system for voice conference - Google Patents

Abstract

PURPOSE:To surely prevent howling and ring tone by using an echo canceller so as to reduce a bypassed voice signal from a speaker received by 2 microphones. CONSTITUTION:When an echo canceller 6 corrects an adaptive filter 52 only if a voice from a speaker 9 only is inputted to microphones 1a, 1b, the same waveform as that of a signal via a delay circuit DL4 is generated from a bypassed voice signal 9a. Thus, the two signals are subtracted by a subtractor 51 to make it possible that the transmission signal is made nearly zero. That is, the bypassed signal from the speaker 9 toward the microphones 1a, 1b when viewing from a transmission reception circuit 7 is nearly zero.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a microphone speaker system for audio conferencing, and more particularly to a microphone speaker system for audio conferencing used in an audio conferencing system using a communication line such as a telephone line. .

[Conventional technology]

In general, an audio conference system is a system that connects two or more locations at different locations using a communication line such as a telephone line, and uses a microphone to collect the content of conference participants' statements. In this method, the conference is held by having the contents of the meeting uttered through speakers placed at the designated points. In this audio conference system, in order to prevent howling and ringing, it is necessary to reduce the signal that goes around from the speaker to the microphone. Conventional microphone speaker systems for audio conferences use acoustic coupling by phase inversion addition as shown in Figure 2. There is a method to reduce it.

In FIG. 2, the conventional microphone speaker system for audio conferencing has microphones 10a and 10b placed on concentric circles equidistant from the speaker 16, and the audio signal arriving at the transmitting/receiving circuit 14 from the receiving line 18 is passed through the amplifier 15. The sound is amplified by speaker 16. This signal is input in the same phase to the microphones 10a and IQb arranged at equal distances. A signal input to microphone 10a is amplified by amplifier 11a, and a signal input to microphone 10b is similarly amplified by amplifier 11b.

The output signal of the amplifier 11b is converted to 180° by the phase inversion circuit 12.
Reverse the phase. By adding this anti-phase signal and the normal phase signal output from the amplifier 11a in the adder 13, the output of the The upper part prevents noise and howling.

[Problem to be solved by the invention]

In the conventional audio conferencing microphone speaker system described above, the signals input to the two microphones are not input in the same phase due to a slight difference in the distance between the microphones, and the microphones' orientations and input sensitivities are slightly different. Since the signals may not necessarily be input in the same phase and the same waveform, there is a drawback that the effect of reducing the wrap-around signal from the speaker to the microphone due to the effect of anti-phase addition is reduced.

[Means to solve the problem]

The audio conferencing microphone speaker system of the present invention includes:
a delay circuit for delaying the output signal of the first microphone using a microphone and a speaker; and a delay circuit connected between the output of the second microphone and the output of the delay circuit to amplify the sound from the speaker. an echo canceller for canceling the output signal of the delay circuit of the voice sound;
are doing.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In FIG. 1, this embodiment uses a microphone la.

1b, an amplifier 2a that amplifies the audio from the microphone 1a, an amplifier 2b that amplifies the audio from the microphone 1b, and an A/D that converts the audio from the amplifier 2a into A/D.
The converter (A/D) 3a and the audio from the amplifier 2b are
An A/D converter (A/D) 3b that performs D conversion, a delay circuit (DL) 4 that delays the output signal of the A/D converter (A/D) 3a, and an A/D converter (A/D) 3a that delays the output signal of the A/D converter (A/D) 3a. D) Adaptive filter 52 and adaptive filter 5 that adaptively modify the output signal of 3b
an echo canceller 5 having a subtracter 51 that subtracts the output signal of the delay circuit (DL) 2 and the output signal of the delay circuit (DL) 4; ) 6, a transmitting/receiving circuit 7 which sends the output signal of the D/A converter (D/A) 6 to the transmitting line 20 and receives the input signal from the receiving line 21, and amplifies the input signal from the transmitting/receiving circuit 7. It has an amplifier 8 and a speaker 9 that amplifies the input signal from the amplifier 8.

Next, the operation of this embodiment will be explained.

In FIG. 1, microphones 1a, ! =lbij1.
, -5 placed on concentric circles approximately equidistant from speaker 9
~ Indicates the case.

The audio signal arriving from the receiving line 21 to the transmitting/receiving circuit 7 is
The signal is amplified by an amplifier 8 and amplified by a speaker 9. If the loudspeaker signal that is input to the microphone 1a is a wrap-around sound 9a, and the one that is input to the microphone 1b is a wrap-around sound 9b, the wrap-around sound 9a is input to the microphone la.
input from the A/D converter (A/D) via the amplifier 2a.
The digital signal 3a and the loop sound 9b are input from the microphone 1b and sent to the amplifier 2b.
After that, it becomes a digital signal by an A/D converter (A/D) 3b. The output signal of the A/D converter (A/D) 3a is delayed by a delay circuit (DL) 4 and input to an echo canceller 50 and a subtracter 51. In addition, an A/D converter (A/D) 3
The output signal of b is sent to the adaptive filter 5 of the echo canceller 5.
2 and is input to the subtracter 51. The output of the subtracter 51 is guided to an adaptive filter 52 for adaptive correction, and further sent as a transmission signal to a transmission line 20 by a transmission/reception circuit 7 via a D/A converter (D/A) 6.

-151 delay circuit (DL) 4 connects speaker 9 and microphone 1a
distance la and distance 7 between speaker 9 and microphone 1b
1! Considering that b may have a small difference such that la<lb, it is assumed that b has half the delay capacity of the adaptive filter 52 in the echo canceller 5. For example, if the delay capacity of the echo canceller 5 is 40 m5ec, the delay circuit 4 is 2
0 m5eC.

If the echo canceller 5 modifies the adaptive filter 52 only when the audio from the speaker 9 is input to the microphones 1a and 1b, the signal outputted through the adaptive filter 52 will be modified by the loop audio signal 9a. The same waveform as the signal passing through the delay circuit (DL) 4 is generated. Furthermore, by subtracting these two signals using the subtracter 51, it is possible to reduce the transmission signal to almost zero. That is, as seen from the transmitter/receiver circuit 7, the loop signals from the speaker 9 to the microphones la and lb are approximately zero.

〔Effect of the invention〕

As explained above, the present invention reduces the distance between the speaker and the microphone, which was seen in the conventional phase inversion/addition effect, by reducing the wraparound audio signals received by the two microphones from the speaker using echo cancellers. This has the effect of preventing an increase in signals from the speaker to the microphone due to differences in microphone input sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of a conventional audio conference microphone speaker system. la, Ib, 10a, 10b--Microphone, 2a. 2b, 8. lla, llb, 15--...-amplifier,
3a, 3b...A/D converter (A/D),
4...Delay circuit (DL), 5...Echo canceller, 51...Subtractor, 52...
...Adaptive filter, 6...D/A converter (D/
A), 7.14... Transmitting/receiving circuit, 9,16...
...Speaker, 20.17...Transmission line, 21.18...Reception line, 9a, 9b, 16
a, 16b...Audio signal going around from the speaker to the microphone, 13...Adder. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] In a microphone/speaker system for an audio conference using a microphone and a speaker, a first microphone, a second microphone, a speaker, and the first
a delay circuit for delaying the output signal of the second microphone; and a delay circuit connected between the output of the second microphone and the output of the delay circuit to erase the output signal of the delay circuit of the sound amplified from the speaker. What is claimed is: 1. A microphone speaker system for an audio conference, comprising: an echo canceller for reducing a signal that goes around from the speaker to the first and second microphones;