JP3145547B2 - Acoustic echo canceller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a communication line, an indoor sound field control device, and a high-quality audio communication conference device, and a signal of a receiving path appears on a transmission path via an acoustic reflection path. The present invention relates to an acoustic reverberation removing device that removes sound.

[0002]

2. Description of the Related Art In general, acoustic echo cancellers are used for long-distance telephone lines using communication sanitation and submarine cables.
It can be broadly divided into one that removes reflection caused by impedance mismatch of the line-to-wire 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 for generating a pseudo acoustic reverberation and a subtraction circuit. The basic operation of the acoustic reverberation removing device will be described below.

FIG. 6 is a diagram showing a basic configuration of an acoustic reverberation removing apparatus. 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 output from the variable coefficient filter 3 are input to a subtraction circuit 5,
The acoustic reverberation component in the transmission signal is removed, and its 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 product sum 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 product sum circuit 10. The output of the product-sum circuit 10 is output as a pseudo acoustic echo. Receiving signal output terminal 2
And the transmission signal input terminal 4 is 2 in the case of a long-distance telephone line.
The line to line converter is connected to a speaker and a microphone in the case of a loudspeaker system.

[0004] Assuming that the signal propagation characteristics of the acoustic reverberation path are linear and represented by an FIR type digital filter, and using the impulse response h (t) and the input received signal x (t), a sample time interval is obtained. Is T, the acoustic reverberation y _{K at} time kT is represented by y _K = h′x _K (1). Here, h = [h ₁ , h ₂ ,..., H _n ] ′ ′ (2) x = [x _k−1 ,..., X _kn ] ′ ′: Vector transposition.

On the other hand, the estimated value of h at time kT is expressed as h
if s _k, estimated value ys _k of y _k is given by _{ys k = hs k 'x k} (3). In the acoustic reverberation removing device, when there is an audio signal at the receiving signal input terminal 1 and no acoustic signal exists at the transmitting signal input terminal 4 and only acoustic reverberation exists, the acoustic reverberation operation is performed as an adaptive operation state. Generally, a learning identification method is adopted as the 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, the e _k = y _k -ys _k, is 0 <α ≦ 1 (5) e k is referred to as residual acoustic echo. Such a calculation operation is performed in the coefficient correction amount calculation circuit 7. The contents of the pseudo impulse response register 9 include a variable coefficient series h.
_sk is stored. α is a correction loop gain for determining the sensitivity of the estimation, and a larger correction amount can be given as the value is closer to 1.0, but it needs to be changed depending on the near-end noise and the line condition. Also, the acoustic reverberation characteristic of the sound field is
When expressed by an IR digital filter,
Becomes very long construction of several 1000 taps, since the calculation amount involved in the correction amount updating of the variable coefficient series hs _k can not be realized in a small hardware becomes enormous, the dividing process into several stages variable coefficient series hs _k A method of reducing the amount of update calculation in one step is adopted. FIG. 7 shows the acoustic reverberation elimination characteristics when the two-division processing is performed. The case where the division process is not used is also described for comparison. The content of division is 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 amount of calculation in one step can be reduced to 、. Of course, if the number of divisions is increased, the amount of calculation can be reduced in proportion thereto.

When not only acoustic reverberation but also a speech signal is inputted to the transmission signal input terminal, that is, when two-way communication occurs, if the acoustic reverberation removing operation is continued as it is, the residual error signal is increased. As a result, communication quality deteriorates. Therefore, it is necessary to detect the state by some method and immediately stop updating the coefficient 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 that uses the moving average power of a fixed section of the received signal and the moving average power of the fixed section of the transmitted signal as the detection evaluation value of bidirectional communication detection, and observes the state displacement by comparing the two methods. There is a method of observing an increase in power, but the latter can realize high-speed two-way communication detection with a smaller detection delay than the former. FIG. 6 illustrates an example of the acoustic reverberation removing apparatus 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 used as the evaluation value of the two-way communication detection, the problem is that the increase of the error signal is not caused by the occurrence of the two-way communication. It also occurs due to the fluctuation of the acoustic echo path, and if only the short-term moving average power of the error signal is observed, it cannot be distinguished between the two-way communication and the acoustic path fluctuation, which causes erroneous detection. As a countermeasure, there is a method of detecting a change in the estimated instantaneous power distribution of the variable coefficient digital filter in the two-way communication state and the acoustic path fluctuation state to reduce the risk of erroneous detection. However, the amount of calculation involved in observing the power distribution change of the variable coefficient digital filter is enormous. Also, the increase in the amount of calculation by calculating the moving average power of the error signal and using it as an evaluation value at each step is not small. Due to such an increase in the amount of calculation related to the detection of bidirectional communication, there is a problem that the hardware becomes large-scale and the feasibility is lost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and eliminates the above-mentioned problems, realizes stable two-way communication detection which is not affected by the power difference between a received signal and a transmitted signal, and cancels large acoustic echo. It is an object of the present invention to provide an acoustic reverberation removing device that performs acoustic reverberation control while maintaining the amount.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and includes 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 that receives the reception signal input from the reception signal input terminal, a pseudo-impulse response register which stores coefficient sequence of the variable coefficient digital filter, the received signal input to the contents of the pseudo-impulse response register and product-sum operation circuit for performing a convolution operation between the contents of the received signal input registers storing the received signal from the terminal, the input pseudo acoustic echo and generated from the transmission signal input terminal by the product-sum operation circuit A subtraction circuit for taking a difference value between the acoustic reverberation and the subtraction circuit
And error signal output is, the variable coefficient digital filter coefficients sequence of the pseudo impulse response register so as to supply the approximation of the echo is divided into N blocks, total coefficient sequence by M times automatically In the acoustic reverberation removing device configured by a coefficient correction amount calculation circuit that performs control to be updated to and a two-way communication detection circuit for detecting the state when two-way communication occurs on the communication line, a first absolute value output circuit for obtaining a first absolute value of the absolute value of each coefficient of the first-th block of the <br/> false impulse response register, each of the second blocks of the pseudo impulse response register If the output of the second absolute value output circuit for obtaining the absolute value of the coefficient and the output of the first absolute value output circuit is smaller than the interpolation threshold [S1], the value is set to “0”, and the interpolation threshold [S
1] is set to “1” if larger than “1”, and “0” if the output of the first coefficient conversion circuit that outputs the total number of “1” and the output of the second absolute value output circuit is smaller than the interpolation threshold [S1]. And "1" if greater than the interpolation threshold [S1],
"1" and the second coefficient conversion circuit that outputs a total number of, smaller than the difference between the inner挿閾value of the output of the first coefficient conversion circuit and the second coefficient conversion circuit [S2] "0" outputs, internal larger than挿閾value [S2] and the attenuation characteristic monitoring circuit that is configured to output "1", the signal amplitude inner挿閾value of the error signal [+ S3] above or the inner挿閾value [- S3] the following cases outputs "1", the error signal
The signal amplitude of the signal is the interpolation threshold [+ S3] and the interpolation threshold [-S
3] and non-linear transformation processing circuit for outputting "0" when there between, and the "1" of the non-linear transformation processing circuit "0"
The number of binary present in a certain section of the series "1" and the predetermined interval movement integrating circuit that outputs while moving the steps every predetermined section consisting of the output inner挿閾value of the predetermined interval the mobile integrated circuit [S4] The output of the correlation value comparison circuit set to output “0” if smaller than the threshold value and the output of “1” if larger than the interpolation threshold [S4], and the output of the attenuation characteristic observation circuit as the first input. a logical product circuit for the output of the correlation value comparing circuit and a second input from the aND circuit "1"
There the operation of the coefficient correction amount calculating circuit stops when it is output, "0" providing acoustic echo cancellation apparatus the coefficient update is performed to continue the operation of the coefficient correction amount calculating circuit when output I do.

[0011]

According to the present invention, the detection delay is extremely small by the above-mentioned means, and the bidirectional communication detection which ensures a stable state when the relative ratio of voice input / output to the sound field changes increases the amount of internal calculation. And a clear and high quality voice communication space can be provided.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a first acoustic reverberation removing apparatus according to the present invention. As shown in FIG. 1, according to the present invention, a 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 operation circuit 7,
Received signal input register 8, pseudo impulse response register 9, product-sum operation circuit 10, and bidirectional communication detection circuit 1
A first absolute value output circuit 12, a second absolute value output circuit 13, and a first coefficient conversion circuit 14 are provided in a device having the same configuration as the acoustic reverberation removing device employing the learning identification method as an adaptive algorithm composed of , A second coefficient conversion circuit 15, an attenuation characteristic observation circuit 16, a non-linear conversion processing circuit 17, a fixed section shift 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 series 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. And a pseudo acoustic reverberation generated by the product-sum operation circuit 10 and the input from the transmission signal input terminal 4. The subtraction circuit 5 for taking a difference value from the acoustic reverberation and the coefficient series of the pseudo impulse response register 9 so that the variable coefficient digital filter 3 supplies an approximate value of the reverberation. Divided into, coefficient correction amount calculating circuit 7 for controlling so as to total coefficient sequence is automatically updated M times
And a bidirectional communication detection circuit 11 for detecting the state of the bidirectional communication on the communication line when the bidirectional communication has occurred. A first absolute value output circuit 12 for obtaining an absolute value of each coefficient, a second absolute value output circuit 13 for obtaining an absolute value of each coefficient of a second block of the pseudo impulse response register 9, 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 [S
The second coefficient conversion circuit 15 that outputs the total number hn2 of “1”, “0” if it is smaller than 1], “1” if it is larger than the interpolation threshold [S1], and the first coefficient The difference h between the output of the conversion circuit 14 and the output of the second coefficient conversion circuit 15
the attenuation characteristic observation circuit 16 set to output “0” if ns is smaller than the interpolation threshold [S2], and to output “1” if ns is larger than the interpolation threshold [S2]; hn1-hn2 (8) If 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 output. When the value is smaller than [+ S3] or larger than the interpolation threshold [-S3], the non-linear conversion processing circuit 17 outputs “0”, and the non-linear conversion processing circuit 17 includes “1” and “0”. The constant section movement integrating circuit 18 that outputs the number of “1” existing in the fixed section of the binary sequence while moving the fixed section for each step, and the output ens of the constant section moving integrating circuit 18 are interpolation threshold values. [S
4], “0” is output, and the interpolation threshold [S
4], the output of the correlation value comparison circuit 19 set to output “1” and the output of the attenuation characteristic observation circuit 16 are used as the first input, and the output of the correlation value comparison circuit 19 is used as the second input. AND circuit 20 which is an input of the AND circuit 20
When "1" is output from the circuit, the coefficient correction amount calculation circuit 7
The acoustic reverberation eliminator is characterized in that the operation of (1) 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 a coefficient sequence of an estimated impulse response stored in the pseudo impulse response register 9 in a steady state when a real female speech signal is input as a reference signal. It can be seen that the attenuation characteristic which is a characteristic of the impulse characteristic of the sound field is maintained.

FIG. 3 shows a case where a real voice signal of a woman is inputted as a reference signal, and a coefficient sequence of an estimated impulse response stored in the pseudo impulse response register 9 when bidirectional communication occurs on the way. is there. As shown by this observation result, since the two-way communication has occurred, the estimation accuracy is extremely deteriorated, the coefficient is disturbed, and the attenuation characteristic as shown in FIG. 2 is not exhibited. The degradation of the damping characteristic of the estimated impulse response due to bidirectional 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 characteristics of the nonlinear conversion processing circuit 17, which has such a ternary correlation coefficient value in order to omit the instantaneous power calculation 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 the interpolation threshold [S3] is reduced, the sensitivity of the two-way communication detection becomes more sensitive, and if it is increased, the sensitivity of the two-way communication detection becomes less sensitive. A two-way communication detection method according to the present invention uses a binary sequence based on the output value and uses it as a second detection evaluation value.

FIG. 5 is a time chart showing the input / output relationship of the AND circuit 20. With such a simple logic circuit, bidirectional communication can be performed at high speed and in a stable manner.

[0018]

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

(1) Structural detection delay of two-way communication detection Since the detection delay can be made extremely small, sound quality deterioration due to disturbance of the coefficient sequence of the adaptive digital filter can be prevented, and a high-quality voice communication space can be realized.

(2) The present invention does not affect the relative ratio of the sound pressure between the reception signal input to the linear system to be controlled and the transmission signal obtained by adding the sound to the echo as the response. Good two-way communication detection can be performed without receiving.

(3) Without deteriorating the acoustic echo canceling performance,
Since the internal operation amount of the adaptive algorithm can be greatly 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 two-way communication detection can be performed, and a high-performance acoustic echo canceller can be provided. .

(5) The two-way communication detection method is a highly versatile method that exhibits the same performance not only for the adaptive algorithm using the learning identification method but also for all other parameter estimation algorithms.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of an acoustic reverberation apparatus 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 at the time of inputting a colored signal used in the present description.

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

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

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

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 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 operation circuit 8 reception signal input register 9 pseudo impulse response register 10 product-sum operation 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 Nonlinear conversion processing circuit 18 Fixed section moving integration Circuit 19 Correlation value comparison circuit 20 AND circuit 21 Short-time moving average power calculation circuit

Claims (1)

(57) [Claims] And 1. A received signal input terminal, and the reception signal output terminal, and a transmission signal input terminal, an input and transmission signal output terminal, a reception signal inputted from said receiving <br/> talk signal input terminal to a variable coefficient digital filter, the contents of the variable coefficient and the pseudo impulse response register coefficient sequence stored in the digital filter, the received signal input registers storing the received signal from the contents of the pseudo-impulse response register the received signal input terminal and product-sum operation circuit for performing a convolution operation between the pseudo acoustic echo and generated by the product-sum operation circuit
A subtraction circuit for calculating a difference value between the acoustic echo input from the transmission signal input terminal, which is calculated output by the subtraction circuit
That an error signal, the divided variable coefficient digital filter the coefficients sequence of the pseudo impulse response register so as to supply the approximation of anti <br/> sound into N blocks, the total coefficient series in M times Acoustic reverberation removal device comprising a coefficient correction amount calculation circuit for performing control so as to be automatically updated, and a two-way communication detection circuit for detecting the state of two-way communication when it occurs on a communication line. in a first absolute value output circuit for obtaining a first absolute value of the absolute value of each coefficient of the first-th block of the pseudo impulse response register,
A second absolute value output circuit for obtaining the absolute value of each coefficient of the second block of the pseudo impulse response register, the <br/> output inner挿閾value of the first absolute value output circuit [S1] than and if smaller "0", as greater if "1" than the inner挿閾value [S1], "1" and the first coefficient conversion circuit for outputting the total number of the second inner output of the absolute value output circuit If it is smaller than the interpolation threshold [S1], it is set to “0”, and the interpolation threshold [S
As greater if "1" than 1], "1" second coefficient conversion circuit and the difference is the interpolation of the output of said first coefficient conversion circuit the second coefficient conversion circuit for outputting the total number of Threshold [S
2], “0” is output, and the interpolation threshold [S
2], and a case where the signal amplitude of the error signal is equal to or more than the interpolation threshold value [+ S3] or equal to or less than the interpolation threshold value [−S3].
In this case, "1" is output, and the signal amplitude of the error signal is between the interpolation threshold [+ S3] and the interpolation threshold [-S3].
A non-linear transformation processing circuit for outputting "0", the number of "1" and "0" is present in the predetermined section of the binary sequence composed of "1" of the non-linear <br/> type conversion processing circuit the output and a constant interval movement integrating circuit that outputs while moving the steps every predetermined interval, the smaller if "0" than the <br/> output inner挿閾value of certain section travel summation circuit [S4], the interpolation A correlation value comparison circuit set to output “1” if the value is larger than a threshold value [S4], and an output of the attenuation characteristic observation circuit as a first input;
A logical product circuit for the output of the correlation value comparing circuit and a second input, before when the AND circuit "1" is outputted
It stops the operation of the serial coefficient correction amount calculating circuit, "0" acoustic echo removing apparatus characterized said that to continue the operation of the coefficient correction amount calculating circuit coefficient updating is performed when the is output.