JPH0456421A - Echo canceller - Google Patents

Abstract

PURPOSE:To maintain echo canceling stably by providing an echo path gain estimate circuit estimating a gain of an echo path depending on a change ratio of a reception level and a transmission level so as to use it as a threshold level of double talk detection. CONSTITUTION:An echo path gain estimate circuit 9 estimates a gain of an echo path from a reception level Lr and a transmission level Ls. This is explained by using a figure in which the X axis indicates the reception level Lr and the Y axis depicts the transmission level Ls. Suppose that the reception level Lr changes with a variable component Dr and the transmission level Ls changes with a variable component Ds, then a ratio of the both k=Ds/Dr indicates a gain of an echo path 7, that is, an attenuation G. When the attenuation G is used for a threshold level K, it is not required to set the threshold level K with respect to the gain G and even when the gain G of the echo path changes halfway, sine the echo path gain estimate circuit 9 always revises the threshold level K, an accurate double talk detection is obtained and excellent echo cancellation is maintained.

Description

[Detailed Description of the Invention] [Summary] Regarding an echo canceller that performs adaptive control in response to a double talk state, the present invention provides an echo canceller that is compatible with double talk so that the threshold value can be made variable according to the gain of the echo path. For the purpose of , a comparator that generates a double talk detection signal when the ratio of both levels exceeds a threshold, and a comparator that estimates the characteristics of the echo path from the received signal and the transmitted signal to generate a simulated echo and convert it from the echo component. In an echo canceller with an adaptive filter that cancels the echo component from the transmitted signal and stops updating the tap coefficients when the double talk detection signal is generated, the echo path is calculated from the ratio of changes in both levels. The echo path gain estimating circuit is configured to estimate the gain of and use it as the threshold value.

[Industrial application field]

The present invention relates to an echo canceller, and more particularly to an echo canceller that performs adaptive control in response to a double talk state.

Echo cancellers are used in various systems such as video conferences, long-distance telephones, and public address telephones to accurately transmit the near-end speaker's signal to the other party by reducing the echo that goes around from the speaker to the microphone. However, since not only the echo but also the originally necessary acoustic signal can be affected by the microphone input signal, normal echo path estimation is stopped for the microphone input signal in this so-called double talk state. An echo canceller that supports double talk is required.

[Prior Art] Fig. 4 shows a conventional echo canceller compatible with double talk, in which 1 is a speaker, 3 is a microphone, and 8 is a characteristic of an echo path 7 from a received signal Rin and a transmitted signal Sin. Estimate and generate a pseudo echo S゛ (echo replica) and subtract it from the echo component S to eliminate the echo component from the transmitted signal and stop updating the tap coefficient when the double talk detection signal is generated. It is an adaptive filter (ADF).

In such an echo canceller, pseudo echo S
゛ is estimated control (tap coefficient update) so that the received signal R4n has characteristics equal to the impulse response of the echo path 7.
The adaptive algorithm is obtained by passing the echo canceller output 5out through the adaptive filter 8.
The goal is to perform feedback control so that the value is minimized.

By the way, in estimating the echo path 7, if the transmitted voice (2) is present, the estimation accuracy will be significantly degraded, and an echo that cannot be completely erased, that is, a residual echo, will be output from the echo canceller output 5out.

Therefore, in such a double talk state, it is necessary to prevent deterioration of estimation accuracy by detecting this and stopping adaptation. Conventionally, the following methods have been used to detect double talk states. Ta.

As shown in FIG. 4, the output L obtained from the received signal Rin and the transmitted signal Sin through level calculation circuits 2 and 4, respectively.
``and Ls are input manually to the level ratio calculation circuit 5, and C=Ls.
/Lr is obtained.

Here, if the transmitted voice V does not exist, the level Ls of the transmitted signal Sin is determined by the level Lr of the received signal Rin and the gain G of the echo path 7, and L s = L r X
G −...■, and C=C.

In addition, if the transmitted voice ■ exists, the transmitted signal Si
Since the level Ls of n increases, L s > L r
It becomes G.

Therefore, the level ratio C and the gain G of the echo path 7 that satisfies the formula (■) are compared as thresholds, and if C>K, it is determined that there is a double talk state, and the adaptation of the adaptive filter 8 is stopped. It is carried out.

[Problem to be solved by the invention]

However, the value of the threshold must be set to an appropriate value according to the gain G of the echo path, and if the gain G changes after being set, the accuracy of the double talk detection operation will deteriorate. Therefore, there have been problems in that the adaptation speed deteriorates, the accuracy of echo path estimation deteriorates, and the residual echo increases.

Therefore, an object of the present invention is to make the threshold value variable in accordance with the gain of the echo path in such a double talk compatible echo canceller.

Means for Solving Problem C] FIG. 1 shows the principle of an echo canceller according to the present invention. In the present invention, the reception level Lr calculated by the reception level calculation circuit 2 and the transmission level calculation circuit 2 are An echo path gain estimating circuit 9 is provided which estimates the gain G of the echo path 7 from the change ratio between both levels of the transmission level Ls calculated by the llI4 and provides a threshold value K to the comparator 6.

[For production]

The echo path gain estimating circuit 9 shown in FIG. 1 estimates the gain of the echo path from the reception level Lr and the transmission level Ls.

The horizontal axis represents the reception level Lr, and the vertical axis represents the transmission level Ls.
To explain with reference to FIG. 2, when the reception level Lr changes by the amount of change Dr and the transmission level LS changes by the amount of change Ds, the ratio of change between the two is k = D s / D
r indicates the gain (attenuation rate) G of the echo path 7, and if this is used as a threshold value, there is no need to set a threshold value K corresponding to the gain G, and the gain of the echo path Even if G changes, the echo path gain estimation circuit 9
Since the threshold value K is continuously updated by , an accurate double talk detection operation can be obtained and a good amount of echo cancellation can be maintained.

[Embodiment] FIG. 3 shows an embodiment of the echo path gain estimation circuit 9 used in the echo canceller according to the present invention shown in FIG. 2
a change calculation circuit 91 connected to the transmission level calculation circuit 4; a change calculation circuit 92 connected to the transmission level calculation circuit 4; and a change calculation circuit 92 connected to the transmission level calculation circuit 4; It consists of a ratio calculation circuit 93 and an averaging circuit 94 that averages the change ratios of the calculation circuit 93 and sends it to the comparator 6 (FIG. 1).

In the operation of this embodiment, the reception level Lr and the transmission level Ls calculated by the reception level calculation circuit 2 and the transmission level calculation circuit 4 are used to calculate the changes Dr and Ds in the change calculation circuits 91 and 92, respectively. do.

Then, a change ratio calculation circuit 93 that manually calculates these changes Dr and Ds calculates k=Ds/Dr.

Here, when the reception level Lr changes in response to a change in the audio signal input to the echo canceller, the transmission level Ls also changes accordingly.

As a result, the relationship between the levels Lr and Ls becomes like a straight line A shown in FIG.

Then, if the transmitting voice ■ exists, the transmitting level Ls
itself becomes higher and there is variation in the position of the straight line, but if the gain (attenuation rate) G of the echo path 7 itself is the same, the average position will be a parallel shift of straight line A as shown in straight line B, and the slope will be k remains unchanged.

In other words, the slope k changes only when the eco path 7 changes for some reason and its gain G changes.

Note that the averaging circuit 94 is provided to average and stabilize temporary fluctuations in the change ratio due to the influence of the transmitted voice V.

〔Effect of the invention〕

According to the echo canceller according to the present invention, since the echo path gain estimation circuit is provided which estimates the gain of the echo path from the change ratio of the reception level and the transmission level and uses it as a threshold for double talk detection, the echo path gain is not known in advance. Even if the echo path gain fluctuates or changes, the echo canceller control operation based on accurate double talk detection can always be obtained, so the echo cancellation operation can be maintained stably.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the principle configuration of an echo canceller according to the present invention, FIG. 2 is a diagram for explaining the present invention in detail, and FIG. 3 shows an embodiment of the echo canceller according to the present invention. Bronk Diagram FIG. 4 is a bronc diagram showing a conventional example. In FIG. 1, 1... Speaker, 2... Reception level calculation circuit, 3... Microphone, 4... Transmission level calculation circuit, 5... Level ratio calculation circuit, 6... Comparator. , 7... Echo path, 8... Adaptive filter, 9... Echo path gain estimation circuit. In the circular, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A reception level calculation circuit (2) that calculates the level of the reception signal to the speaker (1), a transmission level calculation circuit (4) that calculates the level of the transmission signal from the microphone (3), A level ratio calculating circuit (5) that calculates the ratio of both levels, a comparator (6) that generates a double talk detection signal when the ratio of both levels exceeds a threshold, and an echo from the received signal and the transmitted signal. Estimate the characteristics of the path (7) to generate a pseudo echo, and subtract it from the echo component to eliminate the echo component from the transmitted signal, and stop updating the tap coefficient when the double talk detection signal is generated. An echo canceller comprising an adaptive filter (8), characterized in that an echo path gain estimating circuit (9) is provided which estimates the gain of the echo path from the change ratio of both levels and uses it as the threshold value.