JP2691186B2 - Echo canceller for multipoint conference - Google Patents

Description

TECHNICAL FIELD The present invention relates to an echo canceller for a multipoint conference, which cancels a room echo signal which causes a howling and causes hearing loss in a multipoint communication conference. is there.

2. Description of the Related Art With the spread of audio conferences, it has been desired to provide a loudspeaker apparatus having excellent simultaneous call performance and less reverberation. An echo canceller meets this requirement. FIG. 2 shows an example of the configuration of a multipoint communication conference system, showing a three-ground communication conference system consisting of microphones and speaker systems among the grounds A, B, and C. The audio signal input from the microphone 1 of the ground A is the speaker 6 of the ground B and the speaker 10 of the ground C.
A voice signal that is input from the microphone 5 of the ground B in the same manner is amplified by the speaker 11 of the ground C and the ground A.
The audio signal input from the microphone 9 of the ground C is amplified by the speaker 3 of the ground A and the speaker 7 of the ground B to perform the multipoint communication conference. Here, 4, 8 and 12 are echo canceling devices for multipoint conferences, respectively, from the speakers 2 and 3 of the ground A to the microphone 1, from the speakers 6 and 7 of the ground B to the microphone 5, and from the ground speakers 10 and 11 to the microphone 9. The room echo signal that circulates around each is eliminated, which allows a natural voice call without howling or echo.

FIG. 3 is a block diagram showing an example of a conventional echo canceller for a multipoint conference, in order to represent a multi-input 1-output system in a unified manner, for K receiving channels from the first channel to the Kth channel. Shows the case where there is one transmission channel. An example of this kind of configuration is the Institute of Electronics, Information and Communication Engineers, 1986, VO1.J69-A No. 10, "Multi-channel adaptive digital filter". In FIG. 3, reference numeral 13 is a multipoint conference echo canceller, which corresponds to 4, 8 and 12 in FIG. 14 ₁ , 14 ₂ , ..., 14 _K are K listening channels,
15 ₁ , 15 ₂ , ..., 15 _K is K speakers, 16 is microphone,
17 _1, 17 _2, ..., 17 _K is the K estimated echo path, 18 K inputs and one output adder, 19 is a subtracter. The sequential correction of the pseudo echo path in this configuration method is performed as follows.

The input signal to the 14th _K channel k at time t is x _K
(T), assuming that the number of taps of the k-th channel is N _K ,
Channel input signal vector Is k = 1,2, ..., KT: It can be expressed as a transpose of a vector. This vector Signal vector of the echo canceller for multipoint conference If you define It is expressed as _{Assuming that} the i-th coefficient of the _k- th channel pseudo echo path 17K corresponding to the input signal is _k , _i , the k-th channel pseudo echo path Is It is expressed as Pseudo-echo path of echo canceler for multipoint conference If you define The sequential correction equation of the pseudo echo path when the learning identification method is applied is e (t) = d (t) -y (t) d (t): true room echo signal If there is a voice input or K
When there is no individual received signal, the successive correction of the pseudo echo path is prohibited in order to prevent the false correction of the pseudo echo path (double talk control).

With the above configuration, K generated by K received signals is obtained.
The indoor reverberation signals can be simultaneously eliminated.

"Problems to be solved by the invention" However, in a normal multipoint communication conference, it is rare that all the destinations speak at once, and one or several destinations speak, and the remaining ones receive. Becomes This means that the received signals rarely come from all K receiving channels, and normally the received signals come from one channel or several channels, and the remaining channels have no received signals. . Since the amount of cancellation of the echo canceller depends on the level ratio between the echo signal (received signal) and noise, if the pseudo echo path is corrected in this state, the echo path without the received signal will be erroneously corrected and the amount of cancellation will be greatly reduced. There was a problem of deterioration.

The present invention has been made in view of the above problems,
It is an object of the present invention to provide an echo canceller for a multipoint conference that maintains a high canceling amount regardless of a received signal level.

"Means for Solving the Problem" The echo canceller for multipoint conference according to the present invention comprises a reception signal of a plurality of reception channels, and an echo signal received by a microphone via an echo path of each reception signal. From this, by sequentially estimating the impulse response of each echo path, generating a pseudo echo path provided for each of the receiving channels, and by inputting the plurality of received signals to the corresponding one of the pseudo echo paths. In the echo canceller for a multipoint conference, which cancels the echo signal by subtracting the obtained pseudo echo signal from the echo signal with a subtractor, each received signal of each of the plurality of channels, and the output signal of the subtractor And a received / received signal level of each channel and a transmitted / received channel signal level detection circuit for detecting a transmitted signal level received by the microphone; Provided for each channel, the detected reception signal level of the corresponding channel and the detected transmission signal level are respectively input, and the reception signal level is below a predetermined value, or the transmission signal level is above a predetermined value. And a channel-specific control type double-talk control circuit for detecting the above condition as double talk, and when the channel-specific control type double-talk control circuit detects the double-talk, the modification of the pseudo echo path of the corresponding channel is prohibited. Instruct them to do so.

[Embodiment] FIG. 1 shows an embodiment of the present invention, in which parts corresponding to those in FIG. 3 are designated by the same reference numerals. In FIG. 1, reference numeral 20 is a transmitting / receiving channel signal level detection circuit, and 21 is a channel-specific control type double talk control circuit.

Next, the operation will be described. The transmitting / receiving channel signal level detection circuit 20 detects the signal levels of one transmitting channel and K receiving channels, and determines the double talk state. The channel-controlled double-talk control circuit 21 instructs the pseudo echo path determined to be non-double talk (received signal) to be corrected, and the pseudo echo path determined to be double talk (no received signal or transmitted signal). By instructing the correction prohibition, a high erasing amount can be maintained regardless of the received signal level.

[Advantages of the Invention] As described above, the transmission / reception channel signal level detection circuit and the channel-specific control type double talk control circuit are provided, and the double talk control is performed for each channel. It is possible to obtain a reflection erasing device for multipoint conference, which maintains a high erasing amount. Therefore, there is an effect that the call quality in the multipoint communication conference is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram of a configuration example (3 ground) of a multipoint communication conference system, and FIG. 3 is an example of a conventional echo canceller for multipoint conference. It is a block diagram shown.

Claims (1)

(57) [Claims] 1. An impulse response of each echo path is sequentially estimated from the receive signals of a plurality of receive channels and the echo signals received by a microphone via the echo paths of the receive signals, A pseudo echo signal provided for each of the reception channels is generated, and a pseudo echo signal obtained by inputting the plurality of reception signals to corresponding ones of the pseudo echo paths is subtracted from the echo signal by a subtractor. According to the echo canceller for a multipoint conference for canceling the echo signal, each received signal of each of the plurality of channels and the output signal of the subtractor are input, and the received signal level of each channel and the microphone are input to the microphone. A transmission / reception channel signal level detection circuit for detecting the level of the received transmission signal, and the detection reception signal of the corresponding channel provided for each channel. Bell and the detected transmission signal level are respectively input, and a state in which the reception signal level is below a predetermined value or the state in which the transmission signal level is above a predetermined value is detected as double talk. A talk control circuit, wherein the channel-specific control type double talk control circuit, when detecting the double talk, gives an instruction to prohibit the correction of the pseudo echo path of the corresponding channel. Erase device.