JP3121983B2 - 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 Generally, an acoustic reverberation apparatus removes reflection caused by impedance mismatch of a 2-wire 4-wire converter in a long-distance telephone line using communication sanitation and a submarine cable, and a loudspeaker telephone such as a video conference system. , Which can be broadly divided into those that remove the reverberation due to the acoustic coupling of the speaker's voice, and are composed of a correction amount calculation circuit, a variable coefficient filter that generates 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 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 reverberation output from the variable coefficient filter 3 are input to a subtraction circuit 5, where the acoustic reverberation component in the transmission signal is removed, and the output of the subtraction circuit 5 is It 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. In the case of a long-distance telephone line, the reception signal output terminal 2 and the transmission signal input terminal 4
The line transducer is connected to a speaker and 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 ] ′ x = [x _k−1 ,..., X _kn ] ′ (2) ′: Vector transposition.

[0005]

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 (x k e k) / x k 'x k (4). _{However, e k = y k -ys k} ', 0 <a 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.

[0007] _{hs1 k: 0~N / 2 hs2 k} : N / 2~N updating algorithm by applying the divided ranges, Equation (4)
More, expressed as _{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' x k (7) things can be, it is an adaptive algorithm to update 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 voice signal is inputted to the transmission signal input terminal, that is, when two-way communication occurs, if the acoustic reverberation removing operation is continued, 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.

[0009]

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 against this,
A method of detecting a difference between a two-way communication state and an acoustic path fluctuation state using an instantaneous power distribution of a variable coefficient digital filter estimated as shown in -127211 has been proposed. However, in the adaptive algorithm for dividing and updating the coefficients of the variable coefficient digital filter, there are coefficient blocks that are not updated in one step. For that reason,
The comparison of only the former half power and the latter half power of the variable coefficient digital filter has a problem that a detection delay or an erroneous detection is generated, thereby deteriorating the communication quality.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and eliminates the above-mentioned problems. Therefore, even when a coefficient correction amount division update method is adopted in an adaptive algorithm, the present invention can provide a high-speed reception signal and transmission signal. It is an object of the present invention to provide an acoustic reverberation removing apparatus which realizes stable two-way communication detection without being affected by the power difference of the acoustic echo and controls acoustic echo while maintaining a large acoustic echo canceling amount.

[0011]

According to the present invention, there is provided a receiving signal input terminal, a receiving signal output terminal, a transmitting signal input terminal, a transmitting signal output terminal, and a receiving signal input terminal. A variable coefficient digital filter which receives a reception signal input from a terminal, a pseudo impulse response register storing a coefficient series of the variable coefficient digital filter, contents of the pseudo impulse response register, and an input from the reception signal input terminal A product-sum operation circuit for performing a convolution integral operation with a signal; a subtraction circuit for obtaining a difference value between a pseudo acoustic echo generated by the product-sum operation circuit and an acoustic echo input from the transmission signal input terminal; Dividing the coefficient sequence of the pseudo impulse response register into N blocks so that the variable coefficient digital filter provides an approximate value of the echo,
A coefficient correction amount operation circuit for performing a division process such that the entire coefficient sequence is automatically updated every time, an integration circuit for obtaining a short-time moving average power of an error signal output from the subtraction circuit; A two-way communication detection circuit using average power as a detection evaluation value of two-way communication detection, wherein the first power integration for obtaining the total power of the first block of the pseudo impulse response register is performed. A circuit, a second power integrating circuit for calculating the total power of the second block of the pseudo impulse response register, and a coefficient calculating circuit for calculating a primary autocorrelation coefficient of the output of the first power integrating circuit, A block power ratio calculation circuit for calculating a ratio of an output of the first power integration circuit to an output of the second power integration circuit; an output value of the coefficient calculation circuit; and an output value of the block power ratio calculation circuit And the ratio A block evaluation value calculation circuit for calculating the output of the block evaluation value computing circuit, inner 挿閾 value S1
A block comparison circuit that outputs "1" when the error signal is smaller than the threshold value S1 and outputs "0" when the error signal is larger than the interpolation threshold value S1. An error signal power comparison circuit that outputs "1" and outputs "0" if smaller than the interpolation threshold value S2; an output of the block comparison circuit as a first input; The two-way communication detection circuit having two inputs and the operation of the coefficient correction amount calculation circuit are regarded as two-way communication only when both signals input to the two-way communication detection circuit are both "1". An acoustic reverberation remover characterized by stopping the operation of the coefficient correction amount calculation circuit as unidirectional communication in other states and performing acoustic reverberation control of a sound field.

[0012]

According to the present invention, even if the coefficient correction amount division update method is adopted by the above means, the two-way communication detection that ensures high speed even when the relative ratio of voice input / output changes changes the internal operation amount. It can be realized without increasing, and a clear and high quality voice communication space can be provided.

[0013]

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, correction Acoustic reverberation employing a learning identification method as an estimation adaptive algorithm comprising a quantity operation circuit 7, a reception signal input register 8, a pseudo impulse response register 9, a product-sum operation circuit 10, an integration circuit 11, and a two-way communication detection circuit 12. A first power integrating circuit 13, a second power integrating circuit 14, a coefficient calculating circuit 15, a block power ratio calculating circuit 1
6, block evaluation value calculation circuit 17, block comparison circuit 1
8. An error signal power comparison circuit 19 is added.

More specifically, the receiving signal input terminal 1
A reception signal output terminal 2, a transmission signal input terminal 4, a transmission signal output terminal 6, and a variable coefficient digital filter 3 which receives a reception signal input from the reception signal input terminal 1. A pseudo impulse response register 9 storing a coefficient series of the variable coefficient digital filter 3, and a product sum for performing a convolution integral operation of the content of the pseudo impulse response register 9 and an input signal from the reception signal input terminal 1. An arithmetic circuit 10; a subtraction circuit 5 for calculating a difference between the pseudo acoustic echo generated by the product-sum arithmetic circuit 10 and an acoustic echo input from the transmission signal input terminal 4; Divides the coefficient sequence of the pseudo impulse response register 9 into N blocks so as to supply an approximate value of the reverberation, and performs a division process such that the entire coefficient sequence is automatically updated M times. Cormorant and the coefficient correction amount calculating circuit 7, short-time moving average power P of the error signal output from the subtraction circuit
e, and the two-way communication detection circuit 12 using the short-time moving average power as the detection evaluation value of the two-way communication detection. A first power integrating circuit 13 for calculating a total power hp1 of a first block, a second power integrating circuit 14 for calculating a total power hp2 of a second block of the pseudo impulse response register, A coefficient operation circuit 15 for calculating a primary autocorrelation coefficient Ci output from one power integration circuit 13; Ci = (hp1 × hp1 #) / hp12 (8) In the equation (8), hp1 # is the first Represents the first-order delay value of the block total power hp1. The output hp1 of the first power integration circuit 13 and the second power integration circuit 1
4, a block power ratio calculation circuit 16 for calculating the ratio hps of the output hp2, hps = hp2 / hp1 (9) An output value Ci of the coefficient calculation circuit 16 and an output value hps of the block power ratio calculation circuit 17 The block evaluation value calculation circuit 17 for calculating the ratio hpi of: hpi = Ci / hps (10) If the output hpi of the block evaluation value calculation circuit 17 is smaller than the interpolation threshold S1, “1” is output; Interpolation threshold S1
The block comparison circuit 18 that outputs "0" if it is larger than the threshold value, and outputs "1" if the short-time moving average power Pe of the error signal is larger than the interpolation threshold value S2.
If the value is smaller than 2, the error signal power comparison circuit 19 that outputs "0" and the output of the block comparison circuit 18 are set as a first input, and the output of the error signal power comparison circuit 19 is set as a second input. Both the two-way communication detection circuit 12 and two signals input to the two-way communication detection circuit 12 are “1”.
The operation of the coefficient correction amount calculation circuit 7 is stopped as bidirectional communication only in the state of the above, and the operation of the coefficient correction amount calculation circuit 7 is continued as the one-way communication in other states to control the acoustic reverberation of the sound field. This is an acoustic echo canceller.

FIG. 2 shows the transition of the first block total power hp1 in the pseudo impulse response register 9 when white noise is input as a reference signal. As long as such a stable reference signal is supplied, the block total power transiently responds for a certain section, and then becomes saturated, so that good acoustic reverberation can be removed.

FIG. 3 shows an example in which white noise is input as a reference signal.
This is the transition of the first block total power hp1 in the pseudo impulse response register 9 when bidirectional communication occurs halfway. If the bidirectional communication detection is not performed, the power level greatly changes as described above, and good acoustic reverberation cannot be removed. The two-way communication detection method according to the present invention uses a value processed so as to stabilize the power displacement as a first detection evaluation value.

FIG. 4 shows an example of an impulse response characteristic of a sound field observed using a maximum periodic sequence code. When an ideal reference signal such as white noise is input and an acoustic reverberation removal process is performed, an impulse response very similar to this is generated in the pseudo impulse response register 9, but a large disturbance is generated in the transmission signal input terminal 4. , That is, when two-way communication occurs, the impulse response coefficient sequence stored in the pseudo impulse response register does not exhibit the attenuation characteristic as shown in FIG. 4 and the power distribution changes greatly. .
The value obtained by processing this change is used as the second detection evaluation value in the two-way communication detection method according to the present invention.

FIG. 5 shows a result of removing acoustic reverberation when white noise according to the present invention is input as a reference signal and two-way communication is generated halfway. It can be seen that the amount of acoustic echo cancellation before the occurrence of bidirectional communication is stored and the communication state is not degraded and high quality is not lost as compared with the processing without bidirectional communication detection. That is, there is only a detection delay that does not greatly disturb the impulse response stored in the pseudo impulse response register 9.

[0019]

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, it is possible to prevent sound quality deterioration due to 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 pressure of the reception signal which is the input of the linear system to be controlled and the transmission signal in which the sound is added to the reverberation which is the response changes. Good bidirectional communication detection can be performed. (3) The amount of internal calculation of the adaptive algorithm can be significantly reduced without deteriorating the acoustic echo canceling performance, so that 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 reverberation canceller can be provided. (5) The two-way communication detection method is a highly versatile method that exhibits equivalent performance not only to an adaptive algorithm using a learning identification method but also to all other parameter estimation algorithms.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of a first acoustic reverberation removing apparatus of the present description.

FIG. 2 is a diagram showing a transition of the total power of a first block in a pseudo impulse response register used in the present description.

FIG. 3 is a diagram showing a transition of the total power when bidirectional communication of the first block in the pseudo impulse response register used in the present description occurs.

FIG. 4 is a diagram showing an example of an impulse response characteristic of a sound field observed by the maximum period sequence code used in the present description.

FIG. 5 is a diagram illustrating an example of an acoustic echo canceling characteristic when white noise used in the present description is input as a reference signal and two-way communication is generated on the way.

FIG. 6 is a block diagram showing a basic configuration of an acoustic reverberation removing apparatus using a conventional 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 calculation circuit 8 reception signal input register 9 pseudo impulse response register 10 product sum circuit 11 integration Circuit 12 Bidirectional communication detection circuit 13 First power integration circuit 14 Second power integration circuit 15 Coefficient operation circuit 16 Block power ratio operation circuit 17 Block evaluation value operation circuit 18 Block comparison circuit 19 Error signal power comparison circuit

Claims (1)

(57) [Claims] A receiving signal input terminal, a receiving signal output terminal, a transmitting signal input terminal, a transmitting signal output terminal;
A variable coefficient digital filter 3 to which a reception signal input from the reception signal input terminal 1 is input, a pseudo impulse response register 9 storing a coefficient series of the variable coefficient digital filter 3, and contents of the pseudo impulse response register 9 -Sum operation circuit 10 for performing a convolution integral operation of the input signal from the reception signal input terminal 1 and the pseudo-acoustic reverberation generated by the product-sum operation circuit 10 and the sound input from the transmission signal input terminal Subtraction circuit 5 for taking the difference value from the echo
And the coefficient sequence of the pseudo impulse response register 9 is divided into N blocks so that the variable coefficient digital filter 3 supplies an approximate value of the echo, and the entire coefficient sequence is automatically updated M times. A coefficient correction amount calculation circuit 7 for performing such a division process, an integration circuit 11 for obtaining a short-time moving average power of the error signal output from the subtraction circuit 5, and a detection of the short-time moving average power for two-way communication detection. A first power integrating circuit 13 for calculating the total power of the first block of the pseudo impulse response register 9;
A second power integrating circuit 14 for calculating the total power of the second block of the pseudo impulse response register 9 and a coefficient calculating circuit 15 for calculating a primary autocorrelation coefficient output from the first power integrating circuit 13 And the first power integrating circuit 1
3, a block power ratio calculation circuit 16 for calculating an output ratio between the output from the second power integration circuit 14 and the second power integration circuit 14, an output value from the coefficient calculation circuit 15,
A block evaluation value calculation circuit 17 for calculating a ratio with respect to the output value from the block evaluation value calculation circuit 17, and outputs “1” if the output from the block evaluation value calculation circuit 17 is smaller than the interpolation threshold value S 1, The block comparison circuit 18 outputs “0” if the value is larger, and outputs “1” if the short-time moving average power of the error signal is larger than the interpolation threshold S2.
If it is smaller, the error signal power comparison circuit 19 that outputs "0" and the output of the block comparison circuit 18 as a first input and the output of the error signal power comparison circuit as a second input. When both of the two-way communication detection circuit 12 and the two signals input to the two-way communication detection circuit 12 are "1", the operation of the coefficient correction amount calculation circuit 7 is stopped as the two-way communication, An acoustic reverberation removing apparatus characterized in that in the state, the operation of the coefficient correction amount calculating circuit 7 is continued as one-way communication, and acoustic reverberation control of a sound field is performed.