JPS62123837A - Echo canceller - Google Patents

Abstract

PURPOSE:To apply sequential estimate only to the fluctuation of an echo path and to correct a pseudo echo path by identifying an echo path signal and the addition of an object signal depending on the difference from the band of the echo path signal and the object signal. CONSTITUTION:A transmission signal (t) is inputted to a band pass filter 13 on one hand and a part of an object signal v(t) is extracted. Then the level of the signal is detected by a level detection circuit 14 and inputted to a control circuit 15. Thus, the presence of the object signal v(t) is judged and when it is judged as the presence, the operation of an estimate circuit 7 is stopped immediately and the characteristic of the pseudo echo path 8 is kept as it is. On the other hand, when judged to be absent, the operation of the estimate circuit 7 is started immediately, the echo path is subject to sequential estimate based on the inverse of estimate error signal Z(t) and a reception signal x(t) to correct the pseudo echo path 8.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an echo canceling device that eliminates echoes that are caused by the housing and that impede hearing, mainly in a public address telephone system.

(Prior Art) With the spread of audio conferences, it is desired to provide a loudspeaker communication device that can ensure simultaneous communication and has less reverberation. There is an echo canceling device that satisfies this requirement.

FIG. 2 is a block diagram showing an example of a conventional echo canceling device, which includes a receiving system from a receiving end 1 receiving a receiving signal x(t) to a speaker 2, and a receiving system extending from a microphone 3 to a transmitting output end 4.
6 In the communication system from the transmitting system to 6, the training signal source 5 sends a training signal x'
The echo signal y (t) which is input from the speaker 2 to the microphone 3 via the echo path is converted into a sample value by the φ converter 6, and then sent to the estimation circuit 7 to be input into the echo path. The response K (t) is estimated and a pseudo echo path (F'IR filter) 8 is generated. After the call starts, the reception signal X(1) applied to the receiver terminal 1 goes through the echo path and wraps around the microphone 3, resulting in an echo signal y (t
), and a transmitting signal umbrella) to which the target signal v(1) added to the echo path is added is generated. On the other hand, the receiving signal, (1
) is input from the receiving system via the A/l) converter 9 and the pseudo echo path (FIR filter) 8, and the pseudo echo signal z(1) is obtained from the transmitting signal z(t) by the subtracter 10. The echo signal y (t) is canceled by subtracting,
Only the target signal 'v(t) is sent to the transmitting output 4. Here, the pseudo echo path (FIR filter) 8 needs to follow the change in the echo path over time, and the innoculus response is the estimated error signal z (1) = y (t) when the target signal v (t) is not added. -z (t) estimates circuit 7
The pseudo echo path (FIR filter)
8 modifications are made to maintain optimal echo cancellation at all times.

Now, in order to perform sequential estimation, it is necessary to determine the presence or absence of the target signal v(1) and the received signal x(t). Among these, it is easy to judge the received signal (1), but the target signal v(
t), conventionally the transmitting signal z(t) and the receiving signal
The judgment is made by comparing the level of (1) or comparing the level of the estimated error signal (t) and the received signal X(1).

(Problems to be Solved by the Invention) However, in the conventional echo canceling device described above, there are cases where it is not possible to distinguish between fluctuations in the echo path and addition of the target signal, and it often takes an adaptive operation to the fluctuations in the echo path. There was a problem in that malfunctions such as prohibition occurred.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve a method for distinguishing between echo path fluctuations and addition of a target signal, and to provide an apparatus that can successfully successively estimate a pseudo echo path due to echo path fluctuations.

(Another Means to Solve the Problem) In order to achieve the above object, the present invention allows a band-limited received signal to go into and out of the echo path, while passing the output of the microphone through the audio band outside the band of the received signal. The presence or absence of the target signal is determined based on the value of the output signal, and if it is determined that the target signal is present, successive estimation of the pseudo echo path is prohibited.

(Function) As described above, in this invention, the microphone output is input to a band filter whose passband is outside the band of the received signal, and the presence or absence of the target signal is determined based on the value of the output signal. Therefore, if the target signal is present, the sequential estimation is prohibited, and if the target signal is absent, the sequential estimation is restarted, thereby making it possible to reliably correct the pseudo echo path. Therefore, the cancellation characteristics of echo signals are improved, and the above-mentioned problems can be eliminated.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention, in which 1 is a receiver terminal, 2 is a speaker, 3 is a transmitter microphone, 4 is a transmitter output terminal, 5 is a training signal source, and 6 yes converter,
7 is an estimation circuit, 8 is a pseudo echo path (FIR filter), 9
1 is a φ converter, 10 is a subtracter, and 1 is a D/A converter, which are the same as the conventional ones. Reference numeral 12 denotes a band filter that limits the band of the received signal applied to the receiving terminal 1 and sends it to the echo path.The band may be equal to the band of the received signal; in this case, the band of the received signal is limited. This is not a new restriction. 13 is a pantono whose band is an audio band outside the band of the pantono and filter 12! Sufilta, 1
4 is a level detection circuit that detects the output signal of the filter 13, and 15 is a control circuit that receives the level of the detection circuit 14 and controls the estimation circuit 7.

Next, its operation will be explained.

First, before starting a call, the training signal source 5 sends out a training signal '(t) to the receiving system, estimates the echo path innoculus response h (t), and creates a pseudo echo path (F
'IR filter) 8 is generated in the same way as before.

Next, the reception signal x(1) applied to the reception terminal 1 is sent to the echo path from the speaker 2 via the bandpass filter 12. The received signal sent to the echo path is the echo signal y (
t) to the microphone 3, to which the target signal v
(1) is added to the transmitted speech signal z(1), which is input to the microphone 3. By subtracting the estimated signal z(t), which is the output of the pseudo echo path 8, from this signal using the subtracter 10, the transmitted speech output is obtained. Only the target signal v(t) is sent to end 4.

On the other hand, the sending signal z(1) is passed through the band filter 13
is input. Since the filter characteristic of the bandpass filter 13 is such that the audio band outside the band of the bandpass filter 12 is the band, a part of the target signal v (t) is obtained as the output of the band/pass filter 13. This level is detected by the level detection circuit 14 and is input to the control circuit 15. When the presence of the target signal v(1) is determined, the operation of the estimation circuit 2 is immediately prohibited, and the characteristics of the pseudo echo path (FIR filter) 8 are maintained as they are.
If it is determined that there is no target signal v(t), the estimation circuit 7 immediately starts operating, and the echo path is sequentially estimated based on the estimation error signal z(t) and the received signal X(1) to generate a pseudo echo. (FIR filter) 8 is corrected. Incidentally, since the received signal is usually subject to band limitation due to the band of the transmission path or digital signal processing, this embodiment can be easily implemented without additional band limitation using the bandpass filter 12. However, a new band restriction may be applied within a range that does not cause hearing impairment.

In this way, fluctuations in the echo path and addition of the target signal can be distinguished based on the difference in the bands of the echo path signal and the target signal, and the pseudo echo path is corrected by sequentially estimating only the fluctuations in the echo path. I can go.

As is clear from this result, it is possible to maintain optimal echo signal cancellation characteristics compared to the conventional technology.

(Effects of the Invention) As explained in detail above, the present invention inputs the microphone output to a Pantonoyas filter whose passband is outside the band of the received signal, and determines the presence or absence of the target signal based on the value of the output signal. Since the estimating circuit is controlled sequentially, the conventional problems such as the inability to identify the target signal due to fluctuations in the echo path are resolved, and the cancellation characteristics are reliably improved. Therefore, there is an effect that the speech quality in the loudspeaker communication device is improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional echo canceling device when the echo path is a sound field. DESCRIPTION OF SYMBOLS 1... Receiving human power end, 2... Speaker, 3... Microphone, 4... Sending output end, 5... Training signal source, 6... Converter, 7... Estimation Circuit, 8...
・Pseudo echo path (FIR filter), 9...me converter,
10...Subtractor, 11...D/A converter, 12...
- Band/4' filter, 13...Band pass filter, 14...Level detection circuit, 15...Control circuit. Figure 1 Figure 2

Claims (1)

[Scope of Claims] A pseudo echo path is generated by estimating the transfer characteristics of the echo path from the transmitted signal to the echo path and the echo signal after the transmitted signal passes through the echo path, and the transmitted signal is converted into the pseudo echo path. The receiver generates an estimated echo signal obtained by inputting the echo path, and subtracts the estimated echo signal from the echo signal to eliminate the echo signal and extract a target signal added to the echo path. A means for transmitting a band-limited reception signal to an echo path in a communication system echo canceling device consisting of a transmission system and a transmission system, and a means for transmitting a band-limited reception signal to an echo path, and a means for inputting the transmitted echo signal to a microphone in the transmission system, and transmitting the output to the reception system. A means for detecting a target signal by inputting the audio band outside the signal band into a bandpass filter having a passband, and a means for inhibiting the operation of the estimation circuit when the target signal is detected, and operating the estimation circuit when the target signal is not detected. An echo canceling device characterized in that it is provided with a control function for starting the echo path estimation and sequentially estimating the echo path.