JPS61260751A - Acoustic detour signal suppressing circuit of conference talking device - Google Patents

Abstract

PURPOSE:To suppress effectively the acoustic coupling between a microphone and a speaker by using an output obtained through the comparison of a level of an output signal of an echo canceller so as to control plural variable loss circuits and plural switching circuits. CONSTITUTION:An acoustic signal generated from a speaker 14 is inputted to plural microphones 11-1-11-n by acoustic coupling. In this case, the level of the input signal fed to each microphone depends on the structure of the inside of a room or the arrangement between the microphones and the speaker. The sound detour signal is erased by echo cancellers 12-1-12-n arranged to the outputs of each microphone. The remaining output signal after the erasure of the echo canceller is detected by a control circuit 15, the level is compared by a built-in comparator and the result is given to variable loss circuits (or switching circuits) 13-1-13-n connected to the output of each echo canceller as a control signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to an acoustic loop signal suppression circuit for a conference call device applied to a remote conference communication system.

[Prior art]

Conventionally, in a remote conference system using a microphone and a speaker, it is required that no ringing or echoes occur due to acoustic coupling between the microphone and the speaker in the conference room. As methods for this purpose, an echo canceler method that uses an audio switch and an echo canceller method that does not use an audio switch have recently been widely adopted. Generally, for a relatively large number of conference participants, a corresponding plurality of microphones are installed. In order to improve the reduction in the signal-to-noise ratio that occurs in that case, a microphone is connected between the microphone and the mixing circuit, and the sending of the signal from the microphone to the mixing circuit is controlled by the level of the signal. A so-called microphone sound pressure control method is used.

In a conference call device using the above-mentioned microphone sound pressure control method, in order to suppress acoustic feedback signals, conventionally, as shown in FIG. 3. A transmitting variable loss circuit that operates in a complementary manner depending on the magnitude of the sound pressure level between the transmitting and receiving levels. A level suppression circuit consisting of a receiving variable loss circuit 4 and a control circuit 5 is inserted. According to such a configuration.

Although various improvements have been made to the audio detection circuit and operation timing due to the switching operation of the audio switch method, it is said that deterioration in sound quality is unavoidable because it requires a considerably large loss (20 to 30 dB). There were drawbacks.

Furthermore, when considering the introduction of an echo canceller method in place of the voice switch method described above, it is sufficient if the canceled echo path can be assumed to be a linear circuit, but as mentioned above, it is necessary to use multiple microphones and If an acoustic interference suppression circuit based on a control method is used, a nonlinear circuit will be included in the echo path from the receiving output to the transmitting input of the echo canceller, resulting in the problem that echo cancellation performance cannot be obtained. Ta.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned conventional problems.

An acoustic interference signal for a conference call device that can be applied to a conference communication system using multiple microphones, effectively suppressing acoustic coupling between the microphones and speakers, and allowing remote conferences to be held with good audio quality. The purpose is to provide a suppression circuit.

[Structure of the invention]

The acoustic feedback signal suppression circuit of the conference call device according to the present invention includes a plurality of echo cancellers each using output signals from a plurality of microphones as transmitting inputs, input signals from speakers as receiving inputs, and outputs of these echo cancellers. With multiple variable loss circuits or multiple switching circuits connected to each side.

An adder circuit connected to the output side of these variable loss circuits or switching circuits and adding the outputs of these variable loss circuits or switching circuits, and an echo canceller connected to the output sides of the plurality of echo cancellers. The present invention is characterized by comprising a control circuit that controls each of the plurality of variable loss circuits and the plurality of switching circuits using the output obtained by comparing the levels of the output signals.

[Embodiments of the invention]

Next, an embodiment of an acoustic interference signal suppression circuit for a conference call device according to the present invention will be described with reference to one drawing.

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention. This figure shows an echo canceller that uses a transmitting input signal as an input signal, and an input signal from the speaker 14 as a receiving input signal.

13-1 to 13-n are variable loss circuits connected to the output side of each echo canceller, and 15 detects the output signal of each echo canceller, and the output is output from the variable loss circuits 13-1 to 13-n. 16 is an adder circuit that adds the outputs of the variable loss paths 13-1 to 13-n. According to such a configuration, the acoustic signal generated from the input channel 14 is input to the plurality of microphones 11-1 to 11-n by acoustic coupling. in this case.

The magnitude of the input signal applied to each microphone is
The size varies depending on the structure of the room and the placement of each microphone and speaker. This acoustic loop signal is sent to the letter echo canceller 12 placed at each microphone output.
-1 to 12-n. The remaining output signals canceled by the echo canceller are detected by the control circuit 15, and then their levels are compared by built-in comparators.

A control circuit 15 connects variable loss circuits (or switching circuits) 13-1 to the output side of each echo canceller as a control signal.
13-n, when the output signal level of each of the echo cancellers 12-1 to 12-n exceeds a predetermined threshold, the output signal of the echo canceller in which the exceeding signal exists is Second, by comparing the output levels of each echo canceller 12-1 to 12-n, all outputs of the echo canceller having the highest signal level are passed. Method, 3rd, the appropriate side or 1st from the maximum level
Pass the output of the echo canceller in.

Fourthly, the first and second methods or the second and third methods are used together, and the output signal of the echo canceller that exceeds a predetermined threshold is Second. Alternatively, it is conceivable to control by a third method. Note that the above method is an explanation of the case where a 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 noise from increasing.

Note that the above operation is also applicable to the case where there is no reception signal to the speaker 14 and the voices of nine speakers are present, but in that case, each echo canceller is made to stop its adaptive operation.

Even when the received signal and the speaker's signal are present simultaneously, the echo canceller detects a two-way simultaneous conversation state (double talk) and the adaptive operation of the echo canceller is stopped. Even in this case, the echo signal from the received signal to the microphone is effectively suppressed by the received signal before the double talk state in the echo canceller, so that the transmitted signal is not transmitted to the other party. FIG. 2 is a block diagram showing the configuration of a second embodiment according to the present invention. This example is.

Unlike the first embodiment in which all signals are handled as analog signals, the microphones 11-1 to 11-1
11-n output signal to A/D converters 21-1 to 21-n.
After converting it into a digital signal and performing all subsequent processing with the digital signal, a D/A signal is sent to the output side of the countable circuit 24.
The signal is converted back into an analog signal through a converter 25. In this case, Niha, echo canceller 22-1
The reception inputs applied to 22-n are converted into digital signals by the second A/D conversion circuit 27. According to this example, echo cancellers 22-1 to 22-n, control circuit 26° variable loss circuits 23-1 to 23-n, and addition circuit 2
4 series of circuits can be obtained by the dizotal circuit, so the first
This embodiment is smaller and more economical.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to effectively suppress acoustic coupling between multiple microphones and speakers, and to prevent a decrease in the signal-to-noise ratio due to the use of multiple microphones. Therefore, when applied to a remote conference communication system, the naturalness of the conference can be maintained, which has a great effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a first embodiment according to the present invention, FIG. 2 is a block diagram showing the configuration of a second embodiment according to the present invention, and FIG. 3 is a conventional acoustic feedback signal suppression circuit. FIG. 2 is a block diagram showing a configuration example. In the figure, 11-1 to 11-n are microphones. 12-1 to 12-n and 22-1 to 22-n are echo cancellers, 13-1 to 13-n and 23-1 to 23-n are variable loss circuits, 14 is a speaker, and 15.26 is a control circuit. 16.24 is an adder circuit, 21-1 to 2], -n, 27 is an A/D converter, and 25 is a D/A converter.

Claims (1)

[Claims] 1. A plurality of echo cancellers each using output signals from a plurality of microphones as transmitting inputs and input signals from a speaker as receiving inputs, and a plurality of variable loss circuits each connected to the output side of these echo cancellers, or A plurality of switching circuits, a variable loss circuit, or an adding circuit connected to the output side of the switching circuit and adding the outputs of the variable loss circuit or switching circuit, and connected to the output side of the plurality of echo cancellers. and a control circuit that controls each of the plurality of variable loss circuits or the plurality of switching circuits using the output obtained by comparing the levels of the output signals of these echo cancellers. Acoustic feedback signal suppression circuit for the device.