JP2861888B2 - Echo / noise canceller and echo / noise elimination method - Google Patents

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 elimination method for eliminating echo and noise generated by acoustic coupling in a teleconference system connecting a conference room which is far away by video and audio, and a hands-free telephone. .

[0002]

2. Description of the Related Art In a teleconference system, a microphone and a speaker are arranged in the same room in order to perform two-way voice transmission. Therefore, the voice of the participant passes through the transmission path from the microphone, goes around from the speaker in the far-end conference room to the microphone provided in the far-end conference room, and returns again through the transmission path. At this time, the returning sound has a time delay, and an echo due to acoustic coupling occurs, which is heard as an echo. Such a phenomenon also occurs in a hands-free telephone that allows conversation without holding the handset.

[0003] As an echo canceller for canceling an echo generated by acoustic coupling as described above, for example, a "variable step size stochastic gradient algorithm based on reference signal power and noise power" disclosed in IEICE technical report DSP95-23. There is a thing using. FIG. 3 shows the configuration of this echo canceller.

[0004] A system in which the reference input signal 1 received via the first line is converted into an audio signal (acoustic signal) by the speaker 11, and the audio is converted into an electric signal by the microphone 12, and this is output as an output signal. And a system for transmitting data 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, an echo 2 is generated in the acoustic signal. Microphone 12
Converts an acoustic signal including the echo 2 to which an ambient noise 5 is added into an electric signal, and outputs the electric signal as a microphone output signal 6.

The echo canceller 10 receives the reference input signal 1
The acoustic signal output from the speaker 11 based on the
2 to remove the influence of the echo 2 when received by the adaptive filter 100, the reference input signal power estimating circuit 101, and the step size determining circuit 1
02, ambient noise power estimation circuit 103, and subtractor 1
04. The echo canceller 10 is provided with a receiving input terminal 201, a receiving output terminal 202, a transmitting input terminal 203, and a transmitting output terminal 204, and a reference input signal 1 is input via the receiving input terminal 201. The input reference input signal 1 is input to the output terminal 202 on the receiving side.
The microphone output signal 6 output from the microphone 12 is input to the speaker 11 via the transmission-side input terminal 203, and the residual signal 4 described later is output to the transmission-side output terminal 20.
4 is output.

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

The subtracter 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 result of the subtraction as a residual signal 4. The residual signal 4 output from the subtractor 104 is used as an 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. I do.

[0009] The reference input signal power estimating circuit 101 receives the reference input signal 1 input through the receiving side input terminal 201.
And the estimation result (reference input signal power 8)
Is supplied to the step size determination circuit 102.

A step size setting circuit 102 successively determines a step size 7 based on the supplied reference input signal power 8 and ambient noise power 9,
0.

In the echo canceller 100 configured as described above, the adaptive filter 100 includes the input reference input signal 1, the step size 7 supplied from the step size setting circuit 102, and the error returned from the subtractor 102. Using the signal 4, the filter coefficient is updated so that the root-mean-square value of the error signal 4 serving as an output signal is minimized.
Thereby, the effect 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, since the step size is controlled so that the filter coefficients of the adaptive filter 100 are not easily disturbed, an algorithm for designing the adaptive filter so as to minimize the mean square value of the residual signal 4 is used. It can be said that among the (eg, LMS algorithm), one that can achieve the best echo cancellation.

[0013]

However, in the above-described echo canceller, since ambient noise is not eliminated, the ambient signal contains ambient noise in an environment where ambient noise exists. As described above, when the residual signal includes the ambient noise, the echo cannot be eliminated at a level higher than the ambient noise level, so that the echo corresponding to the ambient noise level remains in the residual signal together with the ambient noise. Since this residual signal is sent as it is as a transmission signal,
Ambient noise and echo contained in the residual signal are unpleasant, and there is a problem that communication quality is deteriorated.

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

[0015]

According to the present invention, there is provided an echo / noise canceller comprising: a system in which a reference input signal received via a first line is converted into an audio signal by a speaker; and a voice is converted into an electric signal by a microphone. And a system for transmitting the signal as an output signal on a second line when the audio signal and the ambient noise output from the speaker are received by the microphone and transmitted on 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 a supplied step size, and a pseudo filter generated by the adaptive filter from an output of the microphone. A subtractor that outputs a residual signal by subtracting an echo, a reference input signal power estimation circuit that estimates the power of the reference input signal, An ambient noise power estimation circuit that estimates 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. And a step size determining circuit for determining a step size based on the power of the ambient noise and the power of the ambient noise, and a step size determining circuit for determining the step size based on the power of the reference input signal and the power of the ambient noise. And echo / noise suppressing means for suppressing the echo and the ambient noise contained in the residual signal output from the subtracter by lowering the level of the residual signal.

In the above echo / noise canceller,
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 the ambient noise, and a residual signal output from the subtractor multiplied by the gain coefficient. And a multiplier for outputting as an output signal sent out on the second line. The gain coefficient determination circuit reduces the gain coefficient when the power of the ambient noise is low or when the power of the reference input signal is high. When the power of the ambient noise is large or when the power of the reference input signal is small, the gain coefficient may be determined so as to increase the gain coefficient.

According to the echo / noise elimination method of the present invention, the first
There is a system in which the reference input signal received via the line is converted into an audio signal by a speaker, and a system in which the sound is converted into an electric signal by a microphone and transmitted as an output signal onto the second line. And an echo / noise elimination method in which an audio signal output from the loudspeaker is received by the microphone together with ambient noise and sent out on a line to eliminate an echo and noise, wherein the reference input signal is filtered by an adaptive filter. Processing to generate a pseudo-echo, subtracting it from the output of the microphone to determine 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 Correcting the coefficients of the adaptive filter to minimize the residual signal by using Suppressing the echo and ambient noise that cannot be canceled in the step of reducing the level of the second line and canceling the echo according to the estimated power of the signal and the estimated power of the ambient noise. It is characterized by.

<Operation> In the echo noise canceller and the echo noise elimination method of the present invention configured as described above, the influence of the echo and the ambient noise that cannot be completely eliminated only by the elimination of the echo by the adaptive filter is second. Since the noise is suppressed by lowering the line level, the echo and the ambient noise are not jarring to the far-end talker (the far-end talker connected via the telephone line).
Further, reception of voice from the far-end speaker and 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 the 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 sound of the near-end speaker is suppressed or the ambient noise is reduced when the sound from the far-end speaker is received. There is no repression.

In the present invention, when the echo / noise suppressing means comprises 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 small or when the power of the reference input signal is large, and when the power of the ambient noise is large,
Alternatively, when the power of the reference input signal is small, the gain is reduced when the voice from the far-end speaker is being received, so that the ambient noise is suppressed by the gain coefficient being reduced. In the state where the voice is being input, the gain coefficient is increased and the voice is transmitted over the line without being suppressed.

[0020]

Next, an embodiment 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 one embodiment of the present invention.

The echo / noise canceller of this embodiment is
Gain coefficient determining circuit 300 as echo / noise suppressing means
The configuration is the same as that of the conventional echo canceller shown in FIG. 3 except that a multiplier 301 is provided.
The same components are denoted 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 is supplied. The ambient noise power 9 estimated by the ambient noise power estimation circuit 103 is supplied to the step size determination circuit 102 and is also supplied to the gain coefficient determination circuit 300.

The gain coefficient determination circuit 300 determines a 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. This is supplied to the multiplier 301.

The multiplier 301 includes a gain coefficient determining 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 residual signal 4 has a gain coefficient of 3
02 and outputs the multiplication result to the transmission-side output terminal 204.

In the echo canceller of the present 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 transmission-side output terminal 204, thereby enabling adaptive control. The effect of the echo and ambient noise that cannot be completely eliminated by the function of eliminating the echo by the filter 100 alone is removed.

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

The ambient noise 5 received by the microphone 12 includes the voice of the near-end speaker and the ambient noise.
Therefore, when the ambient noise power 9 is large, it can be assumed that a voice is being input by the near-end speaker at the microphone 12, and conversely, when the ambient noise power 9 is small, the sound is input by the near-end speaker. It can be assumed that no speech has been input and that no speech or speech from the far-end speaker is being received. On the other hand, when the reference signal power 8 is large to some extent, the voice from the far-end speaker is being received. When the reference signal power 8 is small, the voice from the far-end speaker is not received. become. Therefore, when the reference signal power 8 is small, it can be assumed that there is no conversation or a state in which speech is input by the near-end speaker.

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

More specifically, the gain coefficient determination circuit 300 performs a function operation given by G = F (P _r , P _n ). Here, G is a gain coefficient, _Pr is reference signal power, and _Pn is ambient noise power. FIG. 2 shows an example of the function F for achieving the object. In FIG. 2, the function F is represented by a three-dimensional curved surface relating to the reference input power and the ambient noise power with the gain coefficient to be obtained as the z-axis. Here, the given reference signal power _Pr and the ambient noise power P _n A gain coefficient value at which a perpendicular line drawn from the intersection of the three-dimensional curved surface and the three-dimensional curved surface intersect is determined as a gain coefficient.

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

Here, there are two states: 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 call is made by a far-end talker In this state, the reference signal power 8 has a somewhat large value. If there is no ambient noise 5, the adaptive filter 100
Input reference input signal 1, step size setting circuit 1
Step size 7 supplied from 02 and subtracter 1
The filter coefficient is updated using the error signal 4 fed back from 02 so as to minimize the root mean square value of the error signal 4 serving as an output signal. Thereby, the effect 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 an ambient noise 5, the adaptive filter 1
Even after the echo cancellation by 00, ambient noise 5 and an echo corresponding to the level of the ambient noise 5 remain in the residual signal 4. When the level of the ambient noise 5 is large to some extent, it is considered that there has been a voice input by the near-end speaker, and the gain coefficient determination circuit 300 selects a large gain coefficient (normally “1”). As a result, the residual signal in which the ambient noise and the echo remain is transmitted from the transmission-side output terminal 204, and the voice from the near-end speaker is not suppressed. 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 remaining ambient noise and echo. As a result, the output level of the residual signal transmitted from the transmission-side output terminal 204 is reduced, and ambient noise and echo are suppressed. As a result, the remaining echo and ambient noise will not be audible to the far end speaker.

(2) State in which a call is made by a near-end speaker In this state, the ambient noise power 9 has a relatively large value, and the gain coefficient of the gain coefficient determination 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. Note that if the ambient noise power 9 is small to some extent, no voice is input by the near end speaker,
It is considered that there is no conversation or the state where the voice from the far-end speaker is being 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 relatively large value, the above-mentioned (1) the call is made by the far end speaker, and the echo is eliminated by the adaptive filter 100 and the gain is determined by the gain coefficient determination circuit 300 as described above. The determination of the coefficient will be performed.

[0037]

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

According to the first and third aspects of the present invention, the effect of echo and ambient noise that cannot be completely eliminated only by canceling the echo by the adaptive filter is reduced by lowering the level of the second line. Since the noise 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 present invention, there is an effect that an echo / noise canceller having the above effects 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 illustrating a schematic configuration of an example of an echo canceller that cancels an echo generated by acoustic coupling.

[Explanation of symbols]

 REFERENCE SIGNS LIST 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 Estimation circuit 102 Step size determination circuit 103 Ambient noise power estimation circuit 104 Subtractor 201 Reception-side input terminal 202 Reception-side output terminal 203 Transmission-side input terminal 204 Transmission-side output terminal 300 Gain coefficient determination circuit 301 Multiplier 302 Gain coefficient

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 3/20-3/23 H04B 7/005-7/01 H04M 1/58-1/60 H04R 3 / 00 H03H 21/00

Claims (3)

(57) [Claims] 1. A system in which a reference input signal received via a first line is converted into an audio signal by a speaker, and a voice is converted into an electric signal by a microphone, and this is output as an output signal on a second line. And an echo / noise canceller for canceling the echo and noise when the audio signal and the ambient noise output from the speaker are received by the microphone and transmitted to the second line. An adaptive filter that generates a pseudo echo from the reference input signal based on the supplied step size; and a subtractor that subtracts the pseudo echo generated by the adaptive filter from the output of the microphone and outputs a residual signal. A reference input signal power estimating circuit for estimating the power of the reference input signal; and a pseudo echo generated by the adaptive filter and An ambient noise power estimating 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 determining circuit for supplying the same to the adaptive filter, and the level of the second line is reduced and output from the subtractor in accordance with the power of the reference input signal and the power of ambient noise. An echo / noise canceller comprising: echo / noise suppressing means for suppressing echo and ambient noise contained 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 the ambient noise, and a subtractor. A multiplier for multiplying the output residual signal by the gain coefficient, and outputting the multiplied signal as an output signal transmitted on a second line. An echo noise canceller characterized in that the gain coefficient is reduced when the power of the reference input signal is large, and the gain coefficient is increased when the power of the ambient noise is large or the power of the reference input signal is small. 3. A system in which a reference input signal received via a first line is converted into an audio signal by a speaker, and a voice is converted into an electric signal by a microphone, and this is output as an output signal on a second line. An echo / noise elimination method for eliminating an echo and noise that is received by the microphone and transmitted over a line when an audio signal output from the speaker is received by the microphone together with ambient noise. Processing a reference input signal with an adaptive filter to generate a pseudo-echo, subtracting this from the output of the microphone to obtain a residual signal; anda power estimation value of the reference input signal and a power estimation value of the ambient noise. A step of correcting the coefficients of the adaptive filter so as to minimize the residual signal using the step size obtained based on the step size, and canceling the echo. And suppressing the echo and ambient noise that cannot be canceled in the step of reducing the level of the second line and canceling the echo according to the power estimation value of the reference signal and the power estimation value of the ambient noise. And a method for canceling echo noise.