JPH07131387A - Device for eliminating acoustic echo - Google Patents

Abstract

PURPOSE:To provide the good voice communication space by judging the generation of bidirectional communication only when the output of an AND circuit is '1', stopping the operation of a correction amount arithmetic circuit, and reducing the detection delay of the bidirectional communication, and eliminating the tone deterioration. CONSTITUTION:When the output of a constant section movement integration circuit 18 is lower than that of an interpolation threshold value S4, a correlation value comparison circuit 19 outputs '0' and it outputs '1' if it is higher than a threshold value S4. An AND circuit 20 takes the output of an attenuation characteristic observation circuit 16 as the 1st input and takes the output of a comparison circuit 19 as the 2nd input. When the AND circuit 20 outputs '1', a bidirectional communication detection circuit 11 judges that the bidirectional communication is generated to stop the operation of a factor correction amount arithmetic circuit 7 and not performs the factor updating processing. When the circuit 20 outputs '0', the operation of the circuit 7 is continued to update factors. Thus, the detection delay in the bidirectional communication detection is made small and the good voice communication space can be obtained by eliminating the tone deterioration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a communication line, a room sound field control device, and a high-quality voice communication conference device, and an acoustic echo component in which a signal on a receiving path appears in a transmitting path via an acoustic echo path. The present invention relates to an acoustic echo canceller that removes noise.

[0002]

2. Description of the Related Art Generally, an acoustic echo canceller is used in communication hygiene and long-distance telephone lines using a submarine cable.
It can be roughly classified into one that removes reflection caused by impedance mismatch of the line-to-four-line converter and one that removes reverberation due to acoustic coupling of speaker's voice in a loudspeaker such as a video conference system. It is composed of a variable coefficient filter and a subtraction circuit that generate pseudo-acoustic echo. The basic operation of the acoustic echo canceller will be described below.

FIG. 6 is a diagram showing the basic structure of an acoustic echo canceller. The reception signal input terminal 1 is connected to the reception signal output terminal 2, and the reception signal of the reception signal input terminal 1 is branched and supplied to the variable coefficient filter 3 to generate a pseudo echo.
The transmission signal from the transmission signal input terminal 4 and the pseudo acoustic echo that is the output of the variable coefficient filter 3 are input to the subtraction circuit 5,
The acoustic echo component in the transmitted signal is removed, and the subtraction circuit 5
Is output to the transmission signal output terminal 6. The output of the transmission signal output terminal 6 and the signal of the reception signal input terminal 1 are input to the correction amount calculation circuit 7, and the filter coefficient of the variable coefficient filter 3 is corrected by the output of the coefficient correction amount calculation circuit 7. In the variable coefficient filter 3, the reception signal is input to the reception signal input register 8, and the sum of products of the reception signal of the reception signal input register 8 and the pseudo impulse response of the pseudo impulse response register 9 is obtained by the sum of products circuit 10. The output of the sum-of-products circuit 10 is output as a pseudo acoustic echo. Received signal output terminal 2
And the transmission signal input terminal 4 is 2 for a long-distance telephone line.
A line-to-line converter is connected to the speaker and microphone in the case of a loudspeaker telephone system.

Assuming that the signal propagation characteristic of the acoustic echo path is linear and represented by an FIR type digital filter, if the impulse response h (t) and the input received signal x (t) are used, the sampling time interval is Is T, and the acoustic echo y _{K at} time kT is represented by y _K = h′x _K (1). However, h = [h ₁ , h ₂ , ..., H _n ] '(2) x = [x _k-1 , ..., x _kn ]'': transposition of the vector.

On the other hand, the estimated value of h at time kT is h
If s _k , the estimated value ys _k of y _k is given by ys _k = hs _k ′ x _k (3). In the acoustic echo canceller, when there is a voice signal in the reception signal input terminal 1 and there is no voice signal in the transmission signal input terminal 4 and only acoustic echo exists, the echo elimination operation is performed as an adaptive operation state. A learning identification method is generally adopted for this adaptive operation algorithm. Successive correction of hs _k by the learning identification method is performed by _{hs k + 1 = hs k +} α (xk ek) / xk 'x k (4). However, e _k = y _k −y s _k , 0 <α ≦ 1 (5), and e _k is called residual acoustic echo. Such a calculation operation is processed in the coefficient correction amount calculation circuit 7. The contents of the pseudo impulse response register 9 include the variable coefficient series h.
s _k is stored. α is a correction loop gain for determining the sensitivity of estimation, and a larger correction amount can be given as it approaches 1.0, but it must be changed depending on near-end noise and line conditions. Also, the acoustic reverberation characteristics of the sound field are
When expressed with an IR digital filter, several hundreds of
Since it has a long configuration of several thousand taps and the amount of calculation involved in updating the modification amount of the variable coefficient sequence hs _k becomes enormous and cannot be realized by small-scale hardware, the variable coefficient sequence hs _k is divided into several stages. The method of reducing the update calculation amount in one step is performed. FIG. 7 shows acoustic echo canceling characteristics when the two-division processing is performed. The case where division processing is not used for comparison is also described. The division contents are as follows, where N is the total number of variable coefficient sequences.

[0006] _{hs1 k: 0~N / 2 hs2 k} : N / 2~N updating algorithm by applying the divided ranges, Equation (4)
_{More, hs1 k + 1 = hs1 k} + α (x k e k) / x k 'x k (6) hs2 k 1 = hs2 k + α (x k e k) / x k' be represented as x _k (7) it is possible, an adaptive algorithm for updating the entire variable coefficient series hs _k in two steps. Therefore, the calculation amount in one step can be reduced to 1/2, and of course, if the number of divisions is increased, the calculation amount can be reduced in proportion to it.

When not only the acoustic echo but also the voice signal is input to the transmission signal input terminal, that is, when bidirectional communication occurs, if the acoustic echo removal operation is continued as it is, the residual error signal is increased. As a result, communication quality deteriorates. Therefore, the state must be detected by some method to immediately stop the coefficient update of the variable coefficient digital filter. In the bidirectional communication detection, the smaller the detection delay, the less the influence on the communication state. A method of observing the state displacement by comparison between the moving average power of a fixed section of the reception signal and the moving average power of a fixed section of the transmission signal as the detection evaluation value of the two-way communication detection, and a short-time moving average of the error signal. Although there is a method of observing an increase in power, the latter has a smaller detection delay than the former and can realize high-speed two-way communication detection. FIG. 6 shows an example of the acoustic echo canceller when the short-time moving average power of the error signal is used as the detection evaluation value.

[0008]

When the short-time moving average power of the error signal is adopted as the evaluation value for the bidirectional communication detection, the problem is not that the increase in the error signal is caused by the bidirectional communication occurrence. It also occurs due to fluctuations in the acoustic echo path, and if changes in only the short-time moving average power of the error signal are observed, it is not possible to distinguish between bidirectional communication and acoustic path fluctuations, which causes erroneous detection. As a countermeasure against this, a method of reducing the risk of false detection by detecting changes in the instantaneous power distribution of the variable coefficient digital filter estimated in the bidirectional communication state and the acoustic path fluctuation state is considered. However, the amount of calculation involved in observing the power distribution change of the variable coefficient digital filter becomes enormous. Further, the increase in the amount of calculation due to calculating the moving average power of the error signal and using it as the evaluation value in each step is not small. Due to such an increase in the amount of calculation related to the detection of two-way communication, the hardware becomes large-scaled and the feasibility is lost.

The present invention has been made in view of the above points, eliminates the above problems, realizes stable two-way communication detection that is not affected by the power difference between the reception signal and the transmission signal, and eliminates a large acoustic echo. An object is to provide an acoustic echo canceller that performs acoustic echo control while maintaining the amount.

[0010]

SUMMARY OF THE INVENTION The present invention is to solve these problems and comprises a reception signal input terminal, a reception signal output terminal, a transmission signal input terminal, and a transmission signal output terminal. A variable coefficient digital filter that receives the received signal input from the received signal input terminal, a pseudo impulse response register that stores a coefficient sequence of the variable coefficient digital filter, the contents of the pseudo impulse response register, and the received signal input. A product-sum operation circuit that performs a convolution integral operation with the content of the reception-signal input register that stores the reception signal from the terminal, the pseudo-acoustic echo generated by the product-sum operation circuit, and the input from the transmission-signal input terminal A subtraction circuit for taking a difference value from the acoustic echo, and a coefficient of the pseudo impulse response register so that the variable coefficient digital filter supplies an approximate value of the echo. The column is divided into N blocks, and the coefficient correction amount calculation circuit that controls so that the entire coefficient sequence is automatically updated M times and the state when bidirectional communication occurs on the communication line is detected. In the acoustic echo canceller configured with a two-way communication detection circuit for performing the above, a first absolute value output circuit for obtaining an absolute value of each coefficient of the first block of the pseudo impulse response register, and the pseudo impulse response If the output of the second absolute value output circuit for obtaining the absolute value of each coefficient of the second block of the register and the output of the first absolute value output circuit is smaller than the interpolation threshold value [S1], it is set to "0", If it is larger than the interpolation threshold value [S1], it is set to "1" and is set to "1".
If the outputs of the first coefficient conversion circuit that outputs the total number of the first coefficient conversion circuit and the second absolute value output circuit are smaller than the interpolation threshold value [S1], it is set to "0", and if they are larger than the interpolation threshold value [S1]. The difference between the outputs of the second coefficient conversion circuit that outputs the total number of “1” as “1”, the first coefficient conversion circuit, and the second coefficient conversion circuit is the interpolation threshold value [S2]. An attenuation characteristic observing circuit set to output “0” if smaller than the above, and output “1” if larger than the interpolation threshold [S2],
If the signal amplitude of the error signal is larger than the interpolation threshold value [+ S3] or smaller than the interpolation threshold value [-S3], "1" is output, and is smaller than the interpolation threshold value [+ S3]. Alternatively, when it is larger than the interpolation threshold [-S3], a non-linear conversion processing circuit that outputs “0” and a non-linear conversion processing circuit output within a certain interval of a binary sequence consisting of “1” and “0” are output. A constant section movement integration circuit that outputs the number of existing "1" while moving a constant section for each step, and outputs "0" if the output of the constant section movement integration circuit is smaller than the interpolation threshold value [S4] Then, if it is larger than the interpolation threshold value [S4], the correlation value comparison circuit set to output “1” and the output of the attenuation characteristic observation circuit are used as the first input, and the output of the correlation value comparison circuit is The AND circuit used as the second input and "1" is output from the AND circuit. It stops the operation of the coefficient correction amount calculating circuit when the "0" is to provide an acoustic echo removing apparatus for performing coefficient updating to continue the operation of the coefficient correction amount calculating circuit when output.

[0011]

According to the present invention, the detection delay is extremely small by the above means, and the bidirectional communication detection ensuring a stable state increases the internal calculation amount when the relative ratio of the voice input / output to the sound field changes. It is possible to provide a clear and high quality voice communication space.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a first acoustic echo canceller of the present invention. As shown in FIG. 1, according to the present invention, the conventional reception signal input terminal 1, reception signal output terminal 2, variable coefficient digital filter 3, transmission signal input terminal 4, subtraction circuit 5, transmission signal output terminal 6, coefficient correction. Quantity calculation circuit 7,
Received signal input register 8, pseudo impulse response register 9, sum of products operation circuit 10, and bidirectional communication detection circuit 1
The first absolute value output circuit 12, the second absolute value output circuit 13, and the first coefficient conversion circuit 14 are added to the device having the same configuration as the acoustic echo canceling device adopting the learning identification method as the adaptive algorithm configured from 1. , A second coefficient conversion circuit 15, an attenuation characteristic observation circuit 16, a non-linear conversion processing circuit 17, a constant section movement integration circuit 18, a correlation value comparison circuit 19, and a logical product circuit 20.
Has been added.

The receiving signal input terminal 1, the receiving signal output terminal 2, the transmitting signal input terminal 4, the transmitting signal output terminal 6, and the receiving signal input from the receiving signal input terminal 1 are input. The variable coefficient digital filter 3, the pseudo impulse response register 9 storing the coefficient sequence of the variable coefficient digital filter 3, the contents of the pseudo impulse response register 9 and the reception signal from the reception signal input terminal 1. Is input to the product-sum operation circuit 10 for performing a convolution integration operation with the content of the reception-signal input register 8 storing therein, the pseudo-acoustic echo generated by the product-sum operation circuit 10, and the transmission signal input terminal 4. The subtraction circuit 5 which takes the difference value with the acoustic echo and the variable coefficient digital filter 3 supplies N to the coefficient sequence of the pseudo impulse response register 9 so as to supply the approximate value of the echo. Divided into, coefficient correction amount calculating circuit 7 for controlling so as to total coefficient sequence is automatically updated M times
And the acoustic echo canceller composed of the two-way communication detection circuit 11 for detecting the state when two-way communication occurs on the communication line, in the first block of the pseudo impulse response register 9. The first absolute value output circuit 12 for obtaining the absolute value of each coefficient, the second absolute value output circuit 13 for obtaining the absolute value of each coefficient of the second block of the pseudo impulse response register 9, and the first absolute value output circuit 13. If the output of one absolute value output circuit is smaller than the interpolation threshold [S1], it is set to "0", and if it is larger than the interpolation threshold [S1], it is set to "1".
The first coefficient conversion circuit 1 that outputs the total number hn1 of "1"
4 and the output of the second absolute value output circuit are the interpolation threshold value [S
1] if it is smaller than 1], and if it is larger than the interpolation threshold [S1], it is set to "1", and the second coefficient conversion circuit 15 that outputs the total number hn2 of "1" and the first coefficient are output. Output difference h between the conversion circuit 14 and the second coefficient conversion circuit 15
If the ns is smaller than the interpolation threshold [S2], "0" is output, and if it is larger than the interpolation threshold [S2], "1" is output, and hns = hn1-hn2 (8) When the signal amplitude of the error signal is larger than the interpolation threshold [+ S3] or smaller than the interpolation threshold [-S3], "1" is output, and the interpolation threshold is also output. If it is smaller than [+ S3] or larger than the interpolation threshold value [-S3], it is composed of the non-linear conversion processing circuit 17 that outputs "0", and "1" and "0" of the non-linear conversion processing circuit 17. The constant interval movement integrating circuit 18 that outputs the number of “1” existing in the constant interval of the binary sequence while moving the constant interval at each step, and the output ens of the constant interval movement integrating circuit 18 are the interpolation threshold values. [S
4], “0” is output and the interpolation threshold [S
4], the correlation value comparison circuit 19 set to output "1" and the output of the attenuation characteristic observation circuit 16 are used as a first input, and the output of the correlation value comparison circuit 19 is used as a second input. And the logical product circuit 20
When "1" is output from the coefficient correction amount calculation circuit 7
Is stopped, and when "0" is output, the operation of the coefficient correction amount calculation circuit 7 is continued to update the coefficient.

FIG. 2 shows the observed coefficient sequence of the estimated impulse response stored in the pseudo impulse response register 9 in the steady state when the actual female voice signal is input as the reference signal. It can be seen that the attenuation characteristic, which is the characteristic of the impulse characteristic of the sound field, is maintained.

FIG. 3 is an observation of the coefficient sequence of the estimated impulse response stored in the pseudo impulse response register 9 when a bidirectional communication occurs while a female actual voice signal is input as a reference signal. is there. As shown in this observation result, the bidirectional communication occurs, so that the estimation accuracy is extremely deteriorated, the coefficient is disturbed, and the attenuation characteristic as shown in FIG. 2 is not exhibited. The deterioration of the attenuation characteristic of the estimated impulse response due to two-way communication occurs more rapidly than any other change.
The two-way communication detection method according to the present invention employs this sudden change in a macro form and uses it as the first detection evaluation value.

FIG. 4 shows the conversion characteristic of the non-linear conversion processing circuit 17, which has such a three-valued correlation coefficient value in order to omit the calculation of the instantaneous power of the error signal. The interpolation threshold [S3] is set to a value that is not affected by disturbance such as near-end noise. If this interpolation threshold [S3] is made small, the sensitivity of bidirectional communication detection becomes sensitive, and conversely, if it is made large, the sensitivity of bidirectional communication detection becomes insensitive. The two-way communication detection method according to the present invention is one in which a binary sequence is generated based on this output value and is used as the second detection evaluation value.

FIG. 5 is a time chart showing the input / output relationship of the AND circuit 20. In this way, the bidirectional communication can be detected at high speed and stably with a simple logic circuit.

[0018]

As described in detail above, according to the present invention, the following excellent effects are expected.

(1) Since the structural detection delay of the bidirectional communication detection can be made extremely small, it is possible to prevent the sound quality deterioration due to the disturbance of the coefficient sequence of the adaptive digital filter, and to realize a high quality voice communication space.

(2) The present invention is not affected even if the relative ratio of the sound pressures of the reception signal which is the input of the linear system to be controlled and the transmission signal in which voice is added to the echo which is the response changes. Good two-way communication detection can be performed without receiving.

(3) Without degrading the acoustic echo canceling performance,
Since the internal calculation amount of the adaptive algorithm can be significantly reduced, hardware can be realized with a small-scale configuration and cost can be reduced.

(4) Since the threshold value of the error signal can be set low enough not to be affected by near-end noise, high-speed bidirectional communication detection can be performed, and a high-performance acoustic echo canceller can be provided. .

(5) This two-way communication detection method is a highly versatile method that shows equivalent performance not only to the adaptive algorithm using the learning identification method but also to all other parameter estimation algorithms.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an acoustic echo canceller according to the present description.

FIG. 2 is a diagram showing an example of an estimated impulse response coefficient sequence stored in a pseudo impulse response register when a colored signal is used, which is used in the present description.

FIG. 3 is a diagram showing an example of an estimated impulse response coefficient sequence when bidirectional communication of a pseudo impulse response register at the time of input of a color signal used in the present description occurs.

FIG. 4 is a diagram showing an example of conversion characteristics of a non-linear conversion processing circuit given a ternary correlation coefficient used in the present description.

FIG. 5 is a diagram showing an example of a time chart of input / output characteristics of a bidirectional communication detection AND circuit used in the present description.

FIG. 6 is a block diagram showing an example of a basic configuration of an acoustic echo canceller using a conventional general learning identification method.

[Explanation of symbols]

 1 reception signal input terminal 2 reception signal output terminal 3 variable coefficient filter 4 transmission signal input terminal 5 subtraction circuit 6 transmission signal output terminal 7 correction amount calculation circuit 8 reception signal input register 9 pseudo impulse response register 10 sum of products calculation circuit 11 Bidirectional communication detection circuit 12 First absolute value output circuit 13 Second absolute value output circuit 14 First coefficient conversion circuit 15 Second coefficient conversion circuit 16 Attenuation characteristic observation circuit 17 Non-linear conversion processing circuit 18 Fixed interval moving integration Circuit 19 Correlation value comparison circuit 20 AND circuit 21 Short-time moving average power calculation circuit

Claims (1)

[Claims] Claims: 1. A reception signal input terminal, a reception signal output terminal, a transmission signal input terminal, a transmission signal output terminal, and a variable coefficient digital filter having the reception signal input from the reception signal input terminal as an input. And a pseudo impulse response register that stores the coefficient sequence of the variable coefficient digital filter, and a convolution integral operation of the contents of the pseudo impulse response register and the contents of the reception signal input register that stores the reception signal from the reception signal input terminal. A product-sum operation circuit that performs
A subtraction circuit that takes a difference value between the pseudo-acoustic echo generated by the product-sum calculation circuit and the acoustic echo input from the transmission signal input terminal, and the variable coefficient digital filter that supplies an approximate value of the echo. In addition, the coefficient sequence of the pseudo impulse response register is divided into N blocks, and a coefficient correction amount calculation circuit for controlling so that the entire coefficient sequence is automatically updated in M times, and bidirectional communication on a communication line. In the acoustic echo canceller configured with a two-way communication detection circuit for detecting the state when the occurrence of the, the first absolute value for obtaining the absolute value of each coefficient of the first block of the pseudo impulse response register The output circuit, the second absolute value output circuit for obtaining the absolute value of each coefficient of the second block of the pseudo impulse response register, and the output of the first absolute value output circuit are calculated from the interpolation threshold value [S1]. Small And "0", Kere, inner 挿閾 value [S
1] if it is larger than 1], and if the outputs of the first coefficient conversion circuit that outputs the total number of "1" and the second absolute value output circuit are smaller than the interpolation threshold value [S1], then it is "1". 0 ", and if it is larger than the interpolation threshold value [S1], it is set to" 1 ".
If the difference between the outputs of the second coefficient conversion circuit that outputs the total number of "1", the first coefficient conversion circuit, and the second coefficient conversion circuit is smaller than the interpolation threshold value [S2], then " 0 "is output, and if the attenuation characteristic observation circuit is set to output" 1 "if it is larger than the interpolation threshold value [S2], whether the signal amplitude of the error signal is larger than the interpolation threshold value [+ S3]. , 1 is output when it is smaller than the interpolation threshold value [−S3], and it is smaller than the interpolation threshold value [+ S3] or the interpolation threshold value [−S3].
3] is larger than the above, a non-linear conversion processing circuit that outputs “0”, and outputs “1” and “0” of the non-linear conversion processing circuit
The constant interval movement integrating circuit that outputs the number of “1” existing in the constant interval of the binary sequence consisting of Smaller than], output "0", and if larger than the interpolation threshold value [S4], output "1", and the output of the attenuation characteristic observation circuit is the first input. And the operation of the logical product circuit using the output of the correlation value comparison circuit as the second input and the coefficient correction amount calculation circuit when "1" is output from the logical product circuit,
An acoustic echo canceller characterized in that when "0" is output, the operation of the coefficient correction amount calculation circuit is continued to update the coefficient.