JPH0611158B2 - Acoustic sneak signal suppression circuit for conference call equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an acoustic wraparound signal suppression circuit for a conference call device applied to a remote conference communication system.

[Prior art]

Conventionally, in a remote conference system that uses a microphone and a speaker, it is required that howling and echo are not generated due to acoustic coupling between the microphone and the speaker in the conference room. As a method therefor, an echo suppressor method using a voice switch and an echo canceller method not using a voice switch have been widely adopted recently. Generally, for a relatively large number of conference participants, a plurality of microphones corresponding to the conference participants are installed. In order to improve the deterioration of the signal-to-noise ratio that occurs in that case, the transmission from the microphone to the mixing circuit is controlled by the level of the signal by connecting between the microphone and the mixing circuit. A so-called microphone sound pressure control method is used.

In the conference call device using the microphone sound pressure control system, in order to suppress the sound wraparound signal, conventionally, as shown in FIG. 3, the output side of the voice mixing circuit 2 and the input side of the speaker 6 are connected. A level suppression circuit composed of a transmission variable loss circuit 3, a reception variable loss circuit 4, and a control circuit 5 which complementarily operate depending on the magnitude of the sound pressure levels of the transmission level and the reception level is inserted between them. According to such a configuration, various modifications have been made to the voice detection circuit and the operation timing by the switching operation of the voice switch system, but since a considerably large loss (20 to 30 dB) is required, There was a drawback that deterioration of sound quality was unavoidable.

Further, when considering introduction of an echo canceller method instead of the voice switch method, it is sufficient if the cancel echo path can be used in a state in which it can be assumed as a linear circuit. When the acoustic wraparound suppression circuit by the control method is used, a non-linear circuit is included in the echo path from the reception output of the echo canceller to the transmission input, and there is a problem that the echo cancellation performance cannot be obtained.

[Object of the Invention]

An object of the present invention is to solve the above-mentioned conventional problems and to apply it to a conference communication system using a plurality of microphones to effectively suppress acoustic coupling between a microphone and a speaker and to provide remote communication with good voice quality. An object of the present invention is to provide an acoustic sneak signal suppressing circuit for a conference call device capable of holding a conference.

[Structure of Invention]

The acoustic sneak signal suppressor circuit of the conference call device according to the present invention has a plurality of echo cancellers each having an output signal of a plurality of microphones as a voice input and a speaker input signal as a voice input, and outputs of these echo cancellers. A plurality of variable loss circuits, or a plurality of switching circuits connected to the respective sides, and an addition that is connected to the output side of these variable loss circuits or these switching circuits and adds the outputs of these variable loss circuits or these switching circuits A circuit and an output side of the plurality of echo cancellers, and each of the plurality of variable loss circuits or the plurality of switching circuits is controlled by an output obtained by comparing the levels of output signals of the echo cancellers. And a control circuit.

Example of Invention

Next, an acoustic sneak signal suppressing circuit of a conference call device according to the present invention will be described with reference to the drawings with reference to embodiments.

FIG. 1 is a block diagram showing the configuration of the first embodiment according to the present invention. In this figure, 1-1 to 1
-N is a microphone, and 12-1 to 12-n are echo cancellers that use the outputs of the microphones 11-1 to 11-n as the transmission input signals and the input signal of the speaker 14 as the reception input signal. 13-1 to 13-n are variable loss circuits respectively connected to the output sides of the echo cancellers, and 15 detects the output signal of each echo canceller, and outputs from the variable loss circuits 13-1 to 13-n. Is a control circuit for controlling whether or not to derive, and 16 is an adder circuit for adding the outputs of the variable loss circuits 13-1 to 13-n. With such a configuration, the acoustic signal generated from the speaker 14 is transmitted to the plurality of microphones 11-1 to 11-n.
Input by acoustic coupling. In this case, the magnitude of the input signal applied to each microphone varies depending on the indoor structure and the arrangement of each microphone and speaker. The acoustic wraparound signals are echo cancellers 12-1 to 12- arranged at the respective microphone outputs.
erased by n. The remaining output signals erased by the echo cancellers are detected by the control circuit 15 and then level-compared by the built-in comparators, and the variable loss circuits (or the variable loss circuits (or Open / close circuit) 13-1 to 13-n.

Variable loss circuit (or switching circuit) 13 by control circuit 15
As a method of controlling -1 to 13-n, firstly, when the output signal level of each echo canceller 12-1 to 12-n exceeds a predetermined threshold value, the echo in which the excess signal exists A method of passing the output signal of the canceller so as to add it to the subsequent adder circuit 16, and secondly, by comparing the output levels of the echo cancellers 12-1 to 12-n,
A method of passing the output of the echo canceller having the highest signal level, a third method of passing the outputs of the echo canceller of several levels from the maximum level and adding them, and a fourth, the above first It is conceivable to control the output signal of the echo canceller exceeding the predetermined threshold value by the second or third method by using the above method and the second method, or by using the second and the third method together. The above method describes the case where the switching circuit is applied to 13-1 to 13-n, but a variable loss circuit is used instead of the switching circuit to give an appropriate loss to the inferior echo canceller output. This makes it possible to prevent an increase in noise.

The above operation is suitable even when there is no received signal to the speaker 14 and the voice of the speaker exists, but at that time, each echo canceller stops the adaptive operation. Even if the received signal and the speaker's signal are present at the same time,
The echo canceller detects the two-way simultaneous call state (double talk), and the adaptive operation of the echo canceller is stopped. Even in this case, the sneak signal of the reception signal to the microphone is effectively suppressed in the echo canceller by the reception signal before the double-talk state, so that the sneak signal is not transmitted to the other party.

FIG. 2 is a block diagram showing the configuration of the second embodiment according to the present invention. In this example, unlike in the first embodiment, all signals are handled as analog signals, and the output signals of the microphones 11-1 to 11-n are converted into A / D converters 21-1 to 21-n. The digital signal is converted into a digital signal by means of, and all the subsequent processing is performed with a digital signal, and then the analog signal is returned to the output side of the countable circuit 24 through the D / A converter 25. In this case, the reception inputs applied to the echo cancellers 22-1 to 22-n are converted into digital signals by the second A / D conversion circuit 27. According to this example, a series of circuits of the echo cancellers 22-1 to 22-n, the control circuit 26, the variable loss circuits 23-1 to 23-n, and the adder circuit 24 can be obtained by a digital circuit. It is smaller and more economical than the example.

〔The invention's effect〕

As is clear from the above description, according to the present invention, it is possible to effectively suppress the acoustic coupling between the plurality of microphones and the speaker and prevent the deterioration of the signal-to-noise ratio due to the use of the plurality of microphones. Therefore, it is possible to maintain the naturalness of the conference by applying it to the teleconferencing communication system, and the obtained effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment according to the present invention, FIG. 2 is a block diagram showing a configuration of a second embodiment according to the present invention, and FIG. 3 is a conventional acoustic sneak signal suppressing circuit. 3 is a block diagram showing a configuration example of FIG. In the figure, 11-1 to 11-n are microphones, and 12
-1 to 12-n, 22-1 to 22-n are echo cancellers, 13-1 to 13-n, 23-1 to 23-n are variable loss circuits, 14 is a speaker, 15 and 26 are control circuits, 1
6, 24 are adder circuits, 21-1 to 21-n, 27 are A /
D converter, 25 is a D / A converter.

Claims (1)

[Claims] 1. A plurality of echo cancellers, each of which has an output signal of a plurality of microphones as a speech input and an input signal of a speaker as a reception input, and a plurality of variable losses respectively connected to output sides of these echo cancellers. Circuit, or a plurality of switching circuits, these variable loss circuits, or an addition circuit connected to the output side of these switching circuits and adding the outputs of these variable loss circuits or switching circuits, and the outputs of the plurality of echo cancellers And a control circuit connected to the side and controlling each of the plurality of variable loss circuits or the plurality of switching circuits by an output obtained by comparing the levels of output signals of these echo cancellers. An audio sneak signal suppression circuit for conference call equipment.