JPH09116469A - Echo noise cancellor and echo noise canceling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an echo noise cancellor and an echo noise canceling method, by which satisfactory call quality can be maintained even under an environment where surrounding noise exists, by reducing the level of a second line in accordance with the power of a reference input signal and the power of surrounding noise. SOLUTION: An adaptive filter 100 operates in such a way that a step size decision circuit 101 generates pseudo echo 3 in accordance with a step size which is decided based on the outputs of a reference input signal power estimation circuit (RPE) 101 and a surrounding noise power estimation circuit (NPE) 103, and a residual signal in a subtracter 104 with a signal by echo 2 from a microphone 12 and surrounding noise 5 becomes a minimum. Furthermore, a multiplier 301 suppresses the output of the subtracter 104 in accordance with a gain coefficient which a gain coefficient decision circuit 300 decides based on the outputs of RPE 101 and NPE 103. Thus, the influence of echo 2 and surrounding noise 5, which cannot be canceled only by the adaptive filter 100, is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo noise canceller and an echo noise canceling method for canceling echo and noise generated by acoustic coupling in a teleconferencing system or a hands-free telephone that connects a conference room far away by video and audio. .

[0002]

2. Description of the Related Art In a teleconferencing system, a microphone and a speaker are arranged in the same room for bidirectional audio transmission. Therefore, the voices of the participants pass through the transmission path from the microphone, sneak into the microphone provided in the far-end conference room from the speaker of the far-end conference room, and return through the transmission path again. At this time, the returning voice is delayed in time, and an echo due to acoustic coupling is generated, which is heard as an echo. Such a phenomenon also occurs in a hands-free telephone that can talk without holding the handset.

As an echo canceller for canceling the echo generated by the acoustic coupling as described above, for example, "Variable step size stochastic gradient algorithm based on reference signal power and noise power" disclosed in Technical Report DSP95-23 of the Institute of Electronics, Information and Communication Engineers. There is one using. The structure of this echo canceller is shown in FIG.

A system in which the reference input signal 1 received via the first line is converted into a voice signal (acoustic signal) by the speaker 11 and a voice is converted into an electric signal by the microphone 12, and this is used as an output signal. And a system for transmitting on the second line. The audio signal converted by the speaker 11 propagates through the echo path 13 and reaches the microphone 12.
At this time, echo 2 is generated in the acoustic signal. Microphone 12
Converts an acoustic signal including the echo 2 to which ambient noise 5 is added into an electric signal and outputs the electric signal as a microphone output signal 6.

The echo canceller 10 has a reference input signal 1
The acoustic signal output from the speaker 11 based on the
2 is for removing the influence of the echo 2 at the time of being received at 2, and its configuration is the adaptive filter 100, the reference input signal power estimation circuit 101, the step size determination circuit 1
02, ambient noise power estimation circuit 103, and subtractor 1
04. The echo canceller 10 is provided with a receiving side input terminal 201, a receiving side output terminal 202, a transmitting side input terminal 203, and a transmitting side output terminal 204, and a reference input signal 1 is input via the receiving side input terminal 201. The received reference input signal 1 is input to the reception-side output terminal 202.
The microphone output signal 6 output from the microphone 12 and the microphone 12 is input via the transmission side input terminal 203, and the residual signal 4 described later is transmitted to the transmission side output terminal 20.
4 is output.

The adaptive filter 100 has a receiving side input terminal 2
The reference input signal 1 input via 01 is subjected to a convolution operation of the filter coefficient, and the result is supplied to the ambient noise power estimation circuit 103 and the subtractor 104 as a pseudo echo 3.

The subtractor 104 subtracts the pseudo echo 3 supplied from the adaptive filter from the microphone output signal 6 output from the microphone 12, and outputs the subtraction result as the residual signal 4. The residual signal 4 output from the subtractor 104 is used as the output signal of the echo canceller 100, is fed back to the adaptive filter 100, and is further supplied to the ambient noise power estimation circuit 103.

The ambient noise power estimation circuit 103 estimates the power of the ambient noise 5 based on the supplied pseudo echo 3 and residual signal 4 and supplies the estimation result (ambient noise power 9) to the step size determination circuit 102. To do.

The reference input signal power estimation circuit 101 includes a reference input signal 1 input via a reception side input terminal 201.
Estimated power (estimated result) (reference input signal power 8)
Is supplied to the step size determination circuit 102.

The step size setting circuit 102 sequentially determines a step size 7 on the basis of the supplied reference input signal power 8 and ambient noise power 9 and uses it to determine the adaptive filter 10.
0.

In the echo canceller 100 configured as described above, the adaptive filter 100 uses the input reference input signal 1, the step size 7 supplied from the step size setting circuit 102, and the error fed back from the subtractor 102. The signal 4 is used to update the filter coefficient so as to minimize the mean square value of the error signal 4 serving as the output signal.
As a result, the influence of the echo 2 when the acoustic signal output from the speaker 11 based on the reference input signal 1 is received by the microphone 12 is almost eliminated.

In the echo canceller, the step size is controlled so that the filter coefficient of the adaptive filter 100 is not disturbed easily. Therefore, the algorithm for designing the adaptive filter so as to minimize the mean square value of the residual signal 4. It can be said to be one of the ones that can realize the best echo cancellation among (for example, the LMS algorithm).

[0013]

However, since the above-mentioned echo canceller does not cancel the ambient noise, the residual signal includes the ambient noise in the environment in which the ambient noise exists. When ambient noise is included in the residual signal in this way, echoes cannot be canceled above the ambient noise level, so that an echo equivalent to the ambient noise level remains in the residual signal together with ambient noise. Since this residual signal is sent as it is as a transmission signal,
The ambient noise and the echo included in the residual signal are offensive to the ear, and there is a problem that the communication quality deteriorates.

An object of the present invention is to provide an echo noise canceller and an echo noise canceling method which can solve the above problems and maintain good speech quality even in an environment where ambient noise exists.

[0015]

The echo noise canceller of the present invention is a system in which a reference input signal received via a first line is converted into an audio signal by a speaker, and an audio signal is converted into an electric signal by a microphone. And a system for sending this as an output signal to the second line, when the voice signal and ambient noise output from the speaker are received by the microphone and sent to the second line. An echo noise canceller for canceling the echo and noise of the adaptive filter for generating a pseudo echo from the reference input signal based on the supplied step size, and a pseudo filter generated by the adaptive filter from the output of the microphone. A subtractor for subtracting the echo and outputting a residual signal, a reference input signal power estimation circuit for estimating the power of the reference input signal, An ambient noise power estimation circuit for estimating the power of ambient noise received by the microphone, based on the pseudo echo generated by the adaptive filter and the residual signal output from the subtractor, and the reference input signal. Step size determination circuit that determines a step size based on the power of the reference signal and ambient noise, and a step size determination circuit that supplies the step size to the adaptive filter, and the second line according to the power of the reference input signal and the power of ambient noise. And an echo / noise suppressing means for suppressing the echo and the ambient noise included in the residual signal output from the subtractor by reducing the level of.

In the above echo / noise canceller,
The echo / noise suppressing means multiplies the residual coefficient output from the subtracter by the gain coefficient determining circuit that determines the gain coefficient according to the power of the reference input signal and the power of the ambient noise, and the gain coefficient. And a multiplier that outputs as an output signal transmitted on the second line, the gain coefficient determining circuit reduces the gain coefficient when the power of ambient noise is low or when the power of the reference input signal is high. Alternatively, the gain coefficient may be determined such that the gain coefficient is increased when the ambient noise power is high or the reference input signal power is low.

The echo noise canceling method of the present invention is a first method.
There is a system in which the reference input signal received via the line is converted into an audio signal by the speaker, and a system in which the voice is converted into an electric signal by the microphone and is sent as an output signal to the second line. A method of canceling echo and noise in which the voice signal output from the speaker is received by the microphone together with ambient noise and sent out on the line, and the reference input signal is filtered by an adaptive filter. Processing to generate a pseudo echo, subtracting this from the output of the microphone to obtain a residual signal, and a step size determined based on the power estimate of the reference input signal and the power estimate of the ambient noise. To correct the coefficients of the adaptive filter so as to minimize the residual signal to cancel the echo, and the reference input. Suppressing the echo and ambient noise that cannot be canceled in the step of canceling the echo by lowering the level of the second line according to the power estimation value of the signal and the power estimation value of the ambient noise. Is characterized by.

<Operation> In the echo noise canceller and the echo noise canceling method of the present invention configured as described above, the influence of the echo and the ambient noise which cannot be canceled only by canceling the echo by the adaptive filter has a second effect. Since the echo and ambient noise are suppressed by lowering the level of the line, the echo and ambient noise are not annoying to the far-end speaker (the far-end speaker connected through the telephone line).
Further, the reception of voice from the far-end speaker and the voice input by the near-end speaker in the microphone can be estimated based on the power of the reference input signal and the power of ambient noise. Since the level of the line 2 is lowered according to the power of the reference input signal and the power of the ambient noise, the ambient noise is suppressed when the voice of the near-end speaker is suppressed or the voice from the far-end speaker is received. There is nothing that is not suppressed.

In the present invention wherein the echo / noise suppressing means is composed of a gain coefficient determining circuit and a multiplier, the gain coefficient is determined according to the power of the reference input signal and the power of the ambient noise. The level of the second line is determined. The gain coefficient is determined when the power of the ambient noise is low or when the power of the reference input signal is high, and when the power of the ambient noise is high,
Or, it is increased when the power of the reference input signal is low, so in the state where the voice from the far-end speaker is received, the gain coefficient is reduced to suppress the ambient noise and In the state where the voice is input, the gain coefficient is increased and the voice is not suppressed and transmitted to the line.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of an echo noise canceller according to an embodiment of the present invention.

The echo noise canceller of this embodiment is
Gain coefficient determination circuit 300 as echo / noise suppression means
Also, except that the multiplier 301 is provided, the configuration is the same as the conventional echo canceller shown in FIG.
The same components are designated by the same reference numerals and perform the same operation.

The reference input signal power 8 estimated by the reference input signal power estimating circuit 101 is supplied to the step size determining circuit 102 and the gain coefficient determining circuit 3
00. The ambient noise power 9 estimated by the ambient noise power estimating circuit 103 is supplied to the step size determining circuit 102 and the gain coefficient determining circuit 300.

The gain coefficient determination circuit 300 determines the gain coefficient 302 based on the reference input signal power 8 supplied from the reference input signal power estimation circuit 101 and the ambient noise power 9 supplied from the ambient noise power estimation circuit 103. Then, this is supplied to the multiplier 301.

The multiplier 301 is a gain coefficient determination circuit 30.
The gain coefficient 302 output from 0 is used as one input,
The residual signal 4 output from the subtractor 104 to the transmission-side output terminal 204 is used as the other input, and the gain coefficient 3 is added to the residual signal 4.
Multiply by 02 and output the multiplication result to the output terminal 204 on the transmission side.

In the echo canceller of this embodiment configured as described above, the gain coefficient determination circuit 300 and the multiplier 301 suppress the level value of the residual signal transmitted from the output terminal 204 on the transmission side, so that it is adapted. The effect of echo and ambient noise, which cannot be completely canceled by the function of canceling echo by the filter 100, is eliminated.

Hereinafter, how the gain coefficient determination circuit 300 determines the gain coefficient will be described in detail.

The ambient noise 5 received by the microphone 12 includes the voice of the near-end speaker and ambient noise.
Therefore, when the ambient noise power 9 is high, it can be assumed that the near-end speaker is inputting voice into the microphone 12, and conversely, when the ambient noise power 9 is low, the near-end speaker performs the voice input. It can be assumed that no voice is input and that there is no conversation or that the voice from the far-end speaker is being received. On the other hand, when the reference signal power 8 is high to some extent, it means that the voice from the far-end speaker is being received, and when the reference signal power 8 is low, the voice from the far-end speaker has not been received. become. Therefore, when the reference signal power 8 is small, it can be assumed that there is no conversation or that the near-end speaker is inputting voice.

From the above, the gain coefficient determination circuit 30
At 0, the gain coefficient is selected small when the ambient noise power 9 is small, and the gain coefficient is selected large when the ambient noise power 9 is large. Further, when the reference signal power 8 is small, the gain coefficient is selected to be large, and the reference signal power 8
When is small, the gain coefficient is selected small.

Specifically, the gain coefficient determination circuit 300 performs a functional operation given by G = F (P _r , P _n ). Here, G is the gain coefficient, P _r is the reference signal power, and P _n is the ambient noise power. FIG. 2 shows an example of the function F for achieving the purpose. In FIG. 2, the function F is represented by a three-dimensional curved surface regarding the reference input power and the ambient noise power with the obtained gain coefficient as the z-axis, and here, the reference signal power P _r and the ambient noise power P _{n given.} The gain coefficient value at which the perpendicular line drawn from the intersection point of and the three-dimensional curved surface intersects is set as the gain coefficient to be obtained.

Next, the operation of the echo / noise canceller of this embodiment will be briefly described.

Here, there are two states, that is, a state in which the far-end talker is talking and a state in which the near-end talker is talking.
One example will be described.

(1) State in which a far-end talker is making a call In this state, the reference signal power 8 has a relatively large value. If there is no ambient noise 5, the adaptive filter 100
Reference input signal 1 input, step size setting circuit 1
Step size 7 supplied from 02 and subtracter 1
Using the error signal 4 fed back from 02, the filter coefficient is updated so as to minimize the root mean square value of the error signal 4 serving as the output signal. As a result, the influence of the echo 2 when the acoustic signal output from the speaker 11 based on the reference input signal 1 is received by the microphone 12 is almost eliminated. The gain coefficient determined by the gain coefficient determination circuit 300 at this time is “0”.

If there is ambient noise 5, the adaptive filter 1
Even if the echo cancellation by 00 is performed, the ambient noise 5 and the echo corresponding to the ambient noise 5 level remain in the residual signal 4. When the level of the ambient noise 5 is large to some extent, it is considered that there is a voice input by the near-end speaker, and thus the gain coefficient determination circuit 300 selects a large gain coefficient (usually "1"). As a result, the residual signal in which the ambient noise and the echo remain will be transmitted from the transmission-side output terminal 204, and the voice from the near-end speaker will not be suppressed. Further, when the level of the ambient noise 5 is small to some extent, it is considered that there is no voice input by the near-end speaker, and the gain coefficient determination circuit 300 selects a small gain coefficient so as to remove the residual ambient noise and echo. As a result, the output level of the residual signal transmitted from the transmission-side output terminal 204 is lowered, and ambient noise and echo are suppressed. As a result, the residual echo and ambient noise are not annoying to the far-end speaker.

(2) State in which a near-end talker is talking In this state, the ambient noise power 9 has a relatively large value, so that the gain coefficient of the gain coefficient determining circuit 300 is "1". As a result, the residual signal 4 is transmitted from the transmission-side output terminal 204 without suppressing its output level. If the ambient noise power 9 is low to some extent, no voice is input by the near-end speaker,
It is considered that there is no conversation or the voice from the far-end speaker is received, and the gain coefficient is selected small so as to remove the ambient noise according to the level value of the ambient noise power 9.

Here, the voice from the far-end speaker is received,
When the level of the reference signal power 8 becomes a large value to some extent, the above-mentioned state (1) the call by the far-end talker is made, and the echo cancellation by the adaptive filter 100 and the gain by the gain coefficient determination circuit 300 as described above. The coefficient will be determined.

[0037]

Since the present invention is configured as described above, it has the following effects.

In the method according to the first aspect and the method according to the third aspect, the effect of the echo and the ambient noise which cannot be canceled only by canceling the echo by the adaptive filter is reduced by lowering the level of the second line. Since it can be suppressed, there is an effect that good communication quality can be provided even in an environment where ambient noise exists.

According to the second aspect of the invention, there is an effect that an echo / noise canceller having the above effect can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an echo / noise canceller according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of a gain coefficient determination function.

FIG. 3 is a block diagram showing a schematic configuration of an example of an echo canceller that cancels an echo generated by acoustic coupling.

[Explanation of symbols]

 1 Reference Input Signal 2 Echo 3 Pseudo Echo 4 Residual Signal 5 Ambient Noise 6 Microphone Output Signal 7 Step Size 8 Reference Input Signal Power 9 Ambient Noise Power 10 Echo Noise Canceller 11 Speaker 12 Microphone 13 Echo Path 100 Adaptive Filter 101 Reference Input Signal Power Estimating circuit 102 Step size determining circuit 103 Ambient noise power estimating circuit 104 Subtractor 201 Receiving side input terminal 202 Receiving side output terminal 203 Transmitting side input terminal 204 Transmitting side output terminal 300 Gain coefficient determining circuit 301 Multiplier 302 Gain coefficient

Claims (3)

[Claims] 1. A system in which a reference input signal received via a first line is converted into a voice signal by a speaker, and a voice is converted into an electric signal by a microphone, which is used as an output signal on the second line. An echo / noise canceller that eliminates the echo and noise when the voice signal and ambient noise output from the speaker are received by the microphone and sent to the second line. An adaptive filter for generating a pseudo echo from the reference input signal based on the supplied step size, and a subtractor for subtracting the pseudo echo generated by the adaptive filter from the output of the microphone to output a residual signal. A reference input signal power estimation circuit for estimating the power of the reference input signal; a pseudo echo generated by the adaptive filter; An ambient noise power estimation circuit that estimates the power of the ambient noise received by the microphone based on the residual signal output from the subtractor, and a step size based on the power of the reference input signal and the power of the ambient noise. And a step size determination circuit for supplying the same to the adaptive filter, and lowering the level of the second line according to the power of the reference input signal and the power of ambient noise, and outputting from the subtractor. An echo / noise canceller, comprising: an echo / noise suppressing means for suppressing echo and ambient noise included in the residual signal. 2. The echo / noise canceller according to claim 1, wherein the echo / noise suppressing means includes a gain coefficient determining circuit that determines a gain coefficient according to the power of the reference input signal and the power of ambient noise, and a subtractor. And a multiplier that multiplies the output residual signal by the gain coefficient and outputs the product as an output signal to be sent out on the second line. The gain coefficient determination circuit is provided when the ambient noise power is small. , Or an echo noise canceller, wherein the gain coefficient is decreased when the power of the reference input signal is high, and the gain coefficient is increased when the power of the ambient noise is high or the power of the reference input signal is low. 3. A system in which a reference input signal received via a first line is converted into a voice signal by a speaker, and a voice is converted into an electric signal by a microphone, which is used as an output signal on the second line. And an echo / noise canceling method for canceling echoes and noise in which a voice signal output from the speaker is received together with ambient noise by the microphone and sent out on a line, the system comprising: Generating a pseudo echo by processing the reference input signal with an adaptive filter and subtracting this from the output of the microphone to obtain a residual signal; and a power estimation value of the reference input signal and a power estimation value of the ambient noise. The step size determined based on the above is used to modify the coefficient of the adaptive filter so as to minimize the residual signal and cancel the echo. And suppressing the echo and ambient noise that cannot be eliminated in the step of eliminating the echo by lowering the level of the second line according to the power estimation value of the reference signal and the power estimation value of the ambient noise. And an echo / noise canceling method comprising: