JPH04185023A - Echo canceller device - Google Patents

Abstract

PURPOSE:To sufficiently cancel the echo without degrading the quality of speech by changing the clipping level of a nonlinear circuit in proportion to an integral value as the output of an integrating circuit constituting a canceller device to change the clipping level in accordance with the magnitude of echo. CONSTITUTION:The other-party speech signal from a reception-side signal line 1 is inputted to an echo canceller device 9, and the output of this device is sent to an echo line 3 and an false echo line 14. The reception signal sent to the echo line 3 is inputted to the device as an echo signal, and the signal inputted to the false echo line 14 having the same characteristic as the echo line 3 is outputted from the false echo line 14 as a false echo signal approximating the echo signal. This false echo signal is inputted to a nonlinear circuit 16 as a DC signal proportional to the magnitude of the signal by an integrating circuit 17 to control the clipping level. Meanwhile, the false signal is subtracted from the echo signal inputted to an echo canceller circuit 13 to eliminate the echo left unerased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an echo canceller device used in two communication circuits.

[Prior art] In recent years, due to the rapid increase in long-distance communication, especially satellite communication, 1
The presence of echoes occurring in communication lines poses a major problem in terms of call quality because of the magnitude of the circuit delay.

Echo suppressors have traditionally been used to control such echoes. However, since this echo suppressor is based on a switching operation, it has the drawback of causing problems such as cutting off at the beginning of one episode and clicking noise.

Echo canceller devices have been developed to overcome these drawbacks. In this echo canceller device, the characteristics from the receiving output to the transmitter's power are measured based on the speech signal, and the characteristics of the built-in active filter (pseudo echo path) are adjusted to the measured echo path characteristics. By passing the received signal through the echo path, a pseudo echo that approximates the echo signal is created, and by subtracting this pseudo echo from the actual echo signal using a subtractor.

It has a configuration that cancels out echoes.

[Problems to be Solved by the Invention] However, with conventional echo canceller devices, it is difficult to completely cancel echoes due to nonlinear distortion and noise in the echo path, or the influence of the internal filter of the echo canceller.

There is a problem that there is a residual echo after cancellation.

For this reason, conventional techniques have been used to cancel residual echoes by providing a nonlinear circuit (or nonlinear element) in the output section of the echo canceller circuit that does not allow minute signals smaller than a predetermined signal level (clipping level) to pass through. I have to.

That is, for example, as shown in FIG. 2, a speech signal transmitted from the receiving side transmission line 1 is input to the receiving side input terminal 5 of the echo canceller device 9. The signal is then sent to the echo path 3 through the output terminal 6 on the receiver side, and simultaneously to the echo path 14 via the input terminal 10 on the receiver side of the echo canceller circuit 13 .

The reception signal sent to the echo path 3 passes through one echo path 3 and is input as an echo to the transmission side input terminal 7 of the echo canceller device. On the other hand, when the received signal passes through the pseudo echo path 14 having the same characteristics as the first echo path 3, the same pseudo echo as the echo input to the transmitting side input terminal 7 is output. This pseudo echo.

In the subtracter 15 , it is subtracted from the actual echo signal manually input from the transmitting side input terminal 7 via the transmitting side input terminal 11 of the echo canceller circuit 13 .

In addition, the output signal of the subtractor 15 includes a transmission signal and a cancellation residual signal (cancellation residual echo), which is a signal remaining after cancellation. The transmitting side output terminal 1 of the echo canceller circuit 13
Output from 2.

The non-linear circuit 16 connected between the output terminal 12 of the echo canceller circuit 13 and the transmitting side output terminal 8 of the echo canceller device 9 further cancels out the above-mentioned residual signal. Incidentally, this nonlinear circuit 16 is constructed as shown in FIG.
A device with input/output characteristics such as A) or B) is used.

However, with this method, if the prior echo cancellation is not sufficient, if the input signal to the nonlinear circuit is large enough to exceed the clipping level.

Echo cannot be canceled sufficiently. For this reason, if the clipping level of the nonlinear circuit is increased to a level where there is no problem even if the prior cancellation is not sufficient, the low-level portion of the transmitting signal will be caught by this clipping level and will not pass satisfactorily, resulting in a significant drop in call quality. There is a problem of deterioration or deterioration.

That is, in FIGS. 3(A) and 3(B), the nonlinear circuit 16
If the clipping level TH is made small, the residual signal higher than the clipping level TH will pass through the nonlinear circuit, and conversely, if the clipping level TH is too large, a small part of the transmit signal will be blocked by the nonlinear circuit. It will break.

SUMMARY OF THE INVENTION An object of the present invention is to provide an echo canceller device that can sufficiently cancel echoes without causing the above-described deterioration in speech quality.

[Means for Solving the Problems] The echo canceller device of the present invention synthesizes pseudo echoes using a pseudo echo path composed of an adaptive filter having the same characteristics as the echo path from the reception signal output to the transmission signal human power. , an echo canceller device configured to cancel an echo by subtracting the pseudo echo from the actual echo using a subtracter, the echo canceller device being connected to the output of the subtracter;
A nonlinear circuit that prohibits the transmission of signals at minute signal levels.

an integrating circuit connected to the output of the pseudo echo path and taking an integral value of the pseudo echo; and automatically adjusting the clipping level of the nonlinear circuit in proportion to the magnitude of the output signal of the integrating circuit. The purpose is to change the

[Operation] By changing the size of the clipping level of the nonlinear circuit in proportion to the size of the output (integral value) of the integrating circuit as described above, the clipping level changes according to the size of the echo.

Thereby, the echo can be removed by following its size, and therefore, the echo can be sufficiently canceled without causing any substantial deterioration in speech quality.

[Example code] Examples of the present invention will be described below.

FIG. 1 shows an echo canceller device 9 according to an embodiment of the present invention, in which a call signal from the other party transmitted from the receiving side signal path 1 is input to the receiving side input terminal 5 of the echo canceller device 9. The signal is also sent to the echo path 3 and the pseudo echo path 14 via the receiving side output terminal 6, respectively.

The received signal sent to the echo path 3 is input as an echo signal to the transmitted signal input terminal 7 of the echo canceller device 9. In FIG. 1, 4 is a telephone.

Further, the signal input to the pseudo echo path 14 having the same characteristics as the one echo path 3 is outputted from the pseudo echo path 14 as a pseudo echo signal that approximates the echo signal. This pseudo-echo signal is input to the integration circuit 17 , where it is converted into a DC signal proportional to the magnitude of the signal, and then input to the nonlinear circuit 15 . Then, in the nonlinear circuit 16, the magnitude of the clipping level of the nonlinear circuit is controlled in proportion to this input DC signal.

On the other hand, a subtracter 15 subtracts the pseudo echo signal from the echo signal input from the transmit signal input terminal 7 to the echo canceller circuit 13 via the transmit side input terminal 11, and the nonlinear circuit 16 further subtracts the canceled residual echo. is removed.

By the way, in a general phone call, the speakers on both sides do not talk at the same time, and usually only one of them is talking.

Then, when the other party is talking, there is a receiving side signal, and in this case, a signal corresponding to an echo is outputted by the pseudo echo path 14, and is passed through the nonlinear circuit 16 via the integrating circuit 17.
A large DC signal is outputted, and therefore the clipping level of the nonlinear circuit 16 becomes large. As a result, the echo (residual echo) included in the transmitting side signal is completely canceled.

Furthermore, when the near-end speaker is talking, the other party is not talking, so there is no call signal on the receiving side, and therefore there is no pseudo echo signal output from the pseudo echo path 14. No signal is output from the integrating circuit 17, and the clipping level in the nonlinear circuit 16 becomes small.

As a result, the transmitting signal is hardly affected by the nonlinear circuit 16 and is output as is. It is output from the transmission line 2 on the transmitting side.

[Effects of the Invention] As described above, the present invention provides an echo canceller that can perform sufficient echo cancellation without affecting the voice of a single call and without causing a deterioration in call quality. equipment can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an echo canceller device according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional echo canceller device, and FIGS. 3A and 3B are respectively the echo canceller device of FIG. 3 is a graph showing input/output characteristics of a nonlinear circuit in FIG. 1... Receiving side transmission line, 2... Sending side transmission line, 3...
- Echo path, 4...Telephone, 5.10...Receiver side input terminal. 6... Receiving side output terminal, 7.11... Sending side input terminal. 8.12... Sending side output terminal, 9... Echo canceller device, 13... Echo canceller circuit, 14...
- Pseudo echo path, 15... Subtractor, 16... Nonlinear circuit, 17... Integrating circuit. Figure 1 Figure 3 (A) (B) Figure 2

Claims (1)

[Claims] (1) Synthesize a pseudo echo using a pseudo echo path consisting of an adaptive filter with the same characteristics as the echo path from the output of the received signal to the input of the transmitted signal, and subtract the pseudo echo from the actual echo using a subtracter. an echo canceller device configured to cancel echo by canceling an echo, the device comprising: a nonlinear circuit connected to the output of the subtracter and prohibiting transmission of a signal with a minute signal level lower than the clipping level; and a nonlinear circuit connected to the output of the pseudo echo path. an echo, comprising an integrating circuit that takes an integral value of the pseudo echo, and automatically changing the magnitude of the clipping level of the nonlinear circuit in proportion to the magnitude of the output signal of the integrating circuit. canceller device.