JPS61260752A - Acoustic detour signal suppressing circuit of conference talking device - Google Patents

Abstract

PURPOSE:To suppress generation of howling and echo by using a control signal obtained from the result of mutual comparison of output signal levels of microphones and the result of comparison between a reception signal level and a prescribed threshold value so as to control respectively the insertion loss of plural variable loss circuits. CONSTITUTION:Input sound pressure levels fed to microphones 1-1-1-n are compared by a control circuit 16 to control the variable loss circuit of a talker with the largest sound volume into the state without loss and to control the other variable loss circuits into the state with loss. Simultaneously, the control circuit 16 detects the voice level of the reception input and when the level exceeds a prescribed threshold value, the loss of all the variable loss circuits 12-1-12-n is eliminated and a loss is inserted to the variable loss circuit 15. The output of the coupling circuit 13 is fed to the transmission input side of the echo canceller 14 and the transmission output is sent to the opposite party via the variable loss circuit 15. On the other hand, a reception signal is led to the reception input of the echo canceller 14 and outputted through a speaker 6.

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. In a remote conference system using a conference room, it is required that no howling or echo occurs 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. The so-called microphone sound pressure control method is used.

Conventionally, in a conference call device using the above-mentioned microphone sound pressure control method, in order to suppress acoustic feedback signals,
As shown in FIG. 2, a variable transmission loss circuit 3 operates between the output side of the audio mixing circuit 2 and the input side of the speaker 6, depending on the magnitude of the sound pressure level of the transmission level and the reception level.
．． 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 voice detection circuit and operation timing due to the switching operation of the voice switch method, deterioration in sound quality is unavoidable because a considerably large loss (20 to 30 dB) is required. There was a drawback.

In addition, if an echo canceller method is introduced 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. When using an acoustic feedback suppression circuit using a pressure control method,
A nonlinear circuit is 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.

[Purpose of the invention]

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

An acoustic system for a conference call device that is applied to a conference communication system using multiple microphones, effectively suppresses acoustic coupling between the microphones and the sound source, and allows remote conferences to be held with good audio quality. An object of the present invention is to provide an interference signal suppression circuit.

[Structure of the invention]

The acoustic feedback suppression circuit of the conference call device according to the present invention includes a plurality of variable loss circuits each receiving output signals from a plurality of microphones, and is connected to the output side of these variable loss circuits. and an echo canceller having a transmitting input side connected to the output side of the combining circuit and a receiving input side connected to the input side of the speaker.

A control circuit that controls the insertion loss amount of each of the plurality of variable loss circuits using a control signal obtained from a result of mutual comparison of output signal levels of the plurality of microphones and a result of comparison of a reception signal level with a predetermined threshold value. It is characterized by having the following.

[Embodiments of the invention]

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

FIG. 1 is a block diagram showing the configuration of an embodiment according to the present invention. In this figure, 1-1 to 1 to n are microphones, and 6 is a speaker.

12-1 to 12-n are variable loss circuits, 13 is a coupling circuit,
x4 is an echo canceller, 15 is a variable loss circuit, and 16 is a control circuit. Microphones 1-1 to 1. - The input sound pressure level applied to n is detected in the control circuit 16 and the respective sound levels are compared. As a result of this comparison, the corresponding variable loss circuit is controlled to be in a lossless state in order to pass only the voice of the dominant speaker, and all other variable loss circuits are controlled to be in a lossy state. At the same time, a control circuit]6 detects the voice level of the listener's power, and if the level exceeds a predetermined threshold, each variable loss circuit 12-1 to 12-n
control to eliminate all losses. The output of the coupling circuit 13 that combines the respective audio inputs is applied to the transmission input side of the echo canceller 14, and the transmission output is transmitted to the other party via the variable loss circuit 15. On the other hand, the reception signal is guided to the reception input side of the echo canceller 14 and at the same time is amplified through the speaker 6.

The variable loss circuit 15 is controlled so that a loss is inserted only when the received voice level detected by the control circuit 16 exceeds a predetermined threshold. That is, the variable loss circuits 12-1 to 12-n and the variable loss circuit 15 are controlled in a complementary manner depending on the reception level.

The threshold setting for this reception level detection is selected to be equal to the reception level threshold that initiates the adaptive operation of the echo canceller 14 for echo cancellation.

The operation of the circuit configured in this way will be explained below. 1. When only the receiver's human power signal exists, the sound obtained from the speaker 6 is transmitted through all the microphones 1-1 to 1-.
n, is combined in the coupling circuit 13 and input to the echo canceller 14.

The echo canceller 14 functions to cancel these creeping signals. The erased residual portion of the loop signal and the noise in the conference room picked up by all the microphones are each given a loss in a subsequent variable loss circuit and sent to the other party. As a result, not only the loop signal (echo) is not transmitted to the other party, but also the loop gain including the acoustic coupling circuit included in the other party's circuit is suppressed, and as a result, no howling phenomenon occurs. The amount of suppression obtained by an echo canceller is generally 30 dBF7 degrees.

If only a transmitting signal exists, the transmitting voice from the microphone closest to the speaker becomes the dominant call signal, and this and the lossy speech signals from other microphones are synthesized. It is.

The signal is input to the Nicol canceller 14. However, since there is no received signal in the echo canceller 14, the adaptive cancellation operation is stopped, and the combined signal from the speaker is sent as is to the other party. in this case.

The loop signal is in a suppressed state because it is canceled by a training signal applied to the listener's power of the echo canceller before the conference starts.

Furthermore, when two reception signals and two transmission signals exist simultaneously, the transmission signals from all the microphones 1-1 to 1-n are combined without any loss, and the Nicol canceller 14
However, the echo canceller 14 is in the two-way communication detection state, and the correction operation of the echo canceller is stopped immediately after the two-way communication. Therefore, the looping of the received signal is suppressed, and at the same time, the transmitter's signal is transmitted with loss. The loss given at this time corresponds to a maximum of 10 togn when the number of microphones is n, as an example. This makes it possible to suppress an increase in the noise level. In this case, the level of the transmitter's signal will be slightly lower than the level in the case of only the transmitter's signal (without the receiver's power) because the distances between the transmitter and all the microphones are not uniform. However, this should be enough to maintain the naturalness of the conversation.

In the above embodiment, the variable loss circuit 15 inserted on the transmitting output side of the echo canceller 14 is not necessarily required. Without this variable loss circuit, the level of the talker increases somewhat during simultaneous two-way communication, and at the same time the noise energy increases. Furthermore, this state occurs instantaneously during two-way communication, and even at this time, the loop signals are sufficiently suppressed, so the effects of howling and echo are eliminated.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to make the echo paths between the receiver's power and the transmitter's power of the echo canceller have the same characteristics when a received signal is present, and from the speaker to the microphone. Since the echo canceller always effectively cancels the looping signals, it is possible to suppress the occurrence of howling and echo, and it also does not cause large insertion loss in the transmission path, making it suitable for use in conference call systems. The benefits of this method are significant, as it allows the meeting to maintain its natural nature.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment according to the present invention;
FIG. 2 is a block diagram showing an example of the configuration of a conventional acoustic feedback signal suppression circuit. In the figure, 1-1 to 1-n are microphones. 6 is a speaker, 12-1 to 32-n are variable loss circuits, 1
3 is a coupling circuit, and 14 is an echo canceller. 15 is a variable loss circuit, and 16 is a control circuit.

Claims (1)

[Scope of Claims] 1. A plurality of variable loss circuits each receiving output signals from a plurality of microphones; a coupling circuit connected to the output side of these variable loss circuits and coupling the outputs of these variable loss circuits; an echo canceller whose transmitting input side is connected to the output side of the coupling channel and whose receiving input side is connected to the input side of the speaker, the results of mutual comparison of the output signal levels of the plurality of microphones, the receiving signal level and a predetermined value; and a control circuit that controls the amount of insertion loss of each of the plurality of variable loss circuits using a control signal obtained from the result of comparison with a threshold value. 2. In the acoustic feedback signal suppression circuit according to claim 1, a second variable loss circuit is inserted on the transmission output side of the echo canceller, and a control signal obtained from the control circuit controls the plurality of noise signals. An acoustic feedback signal suppression circuit for a conference call device, characterized in that the insertion loss amount of the second variable loss circuit is controlled complementary to the control of the second variable loss circuit.