Patent Translate Powered by EPO and Google Notice This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate, complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or financial decisions, should not be based on machine-translation output. DESCRIPTION JPH11317695 [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-channel acoustic echo cancellation method for canceling acoustic echo which is the cause of howling and hearing impairment in a communication conference system having a multichannel reproduction system, its apparatus and its program recording It relates to the medium. [0002] 2. Description of the Related Art In recent years, with the spread of digital networks such as ISDN, LAN, and the Internet, and the development of high-efficiency coding technology for voice and image, various types of telephone conversations have appeared in addition to conventional telephones. With a TV conference system that allows you to make a call while looking at the other party's face using a large screen TV or a personal computer or work station, a desktop meeting system, etc., it is easy for more than one person to participate in a call and it is more natural In many cases, a speech communication system capable of providing a speech environment is employed. However, this system using a speaker and a microphone is accompanied by the problem of the occurrence of echo and howling, and to avoid this, acoustic echo canceller technology is indispensable. [0003] 09-05-2019 1 In fact, in these situations, acoustic echo canceller devices are widely used, but most of them are for single channel audio, and one system of loudspeakers from one channel to microphones of one channel (channel). Only acoustic wraparounds can be eliminated. On the other hand, in many TV broadcasts, music media, etc., stereo sound is common, and the implementation of such multichannel sound conversion is strongly demanded also for loud speech. Therefore, it is necessary to realize an acoustic echo canceller device for multi-channel audio that enables cancellation of acoustic interference from a plurality of (channel) speakers to a microphone, and in recent years, technical problems and solutions therefor have been realized. The examination of has become active. [0004] Acoustic echo cancellation in a teleconferencing system generally consisting of a receiver system for N (N ≧ 2) channels and a transmitter system for M (M 送 1) channels is conventionally performed according to the configuration shown in FIG. . That is, the N channel echo cancelers 221, 222,..., 22M constituting the echo cancellation unit 22 respectively between the receiving terminals 111, 112,..., 11N of all N channels on the receiving side and the transmitting system of the M channel .., 11 N are connected as acoustic signals by the respective speakers 121, 122,..., 12 N, and echoes (represented by impulse responses h mn) Reverberation) Acoustic echoes that go around each of the microphones 161, 162,..., 16M via the path 15 nm (1 ≦ n ≦ N, 1 ≦ m ≦ M) are eliminated. [0005] The N-channel echo cancelers 221, 222,..., 22M described above have the same configuration for each transmission channel, and for example, the configuration shown in FIG. This is described in the document B. Widrow and S. D. Stearns, "Adaptive signal processing," Prince-Hall, Inc. pp. 198200, (1985), taking the case of two channels as an example. In the configuration of FIG. 2, the reception signals x1 (k), x2 (k),..., XN (k) are respectively input to adaptive filters 2211, 2212, and 221N forming N pseudo echo paths, and the adaptive filter 2211 is , 2212,..., 221N are added by the adder 222 to generate a pseudo echo signal y'm (k), and the pseudo echo signal and the collected signal (echo signal) ym (k) from the microphone 16m are generated. And the error signal (residual echo signal) em (k), which is the output thereof, is fed back to the adaptive filters 2211 to 221N, and received signals x1 (k) to xN (). k), the filter coefficient vector is determined by, for example, the NLMS algorithm so that the error signal em (k) becomes smaller, and the adaptive filters 2211 to 221N are adaptively controlled. 09-05-2019 2 [0006] Although not shown in FIG. 1, in the echo cancellers 221 to 22M, an acoustic signal zm (k) to be originally transmitted is input to the microphones 161 to 16M, and is transmitted through the echo cancellers 221 to 22M. , And to prevent the reproduced sound from the speaker picked up by the microphone from being transmitted together with the signal zm (k) as an echo ym (k). That is, the error signal em (k) output as a result of echo cancellation in FIG. 2 includes the signal zm (k) to be originally transmitted. However, the present invention focuses only on the echo signal ym (k) which is a pickup signal by the microphone of the reproduction sound from the speaker, and does not particularly mention the signal zm (k) to be transmitted. The same applies to the detailed description of the present invention. [0007] When the correlation between the respective reception signals x1 (k) to xN (k) is low, the adaptive filters 2211, 2212,..., 221N can estimate the corresponding echo path with relatively high accuracy, and therefore become the cancellation target It is possible to generate a pseudo echo that accurately simulates an acoustic echo. However, in an actual communication conference, in many cases, when the voice of one speaker is transmitted from the other party on multiple channels and these become receiving signals, there is a very high correlation between the receiving signals, and an adaptive filter Both the convergence speed and the convergence accuracy may deteriorate, and the desired echo cancellation performance may not be obtained. In order to solve this problem, it is possible to perform preprocessing to reduce or change the correlation between the received signals before each received signal is input to the N channel echo canceller 221, 222, ..., 22M. No. 5, 661, 813. [0008] In the configuration shown in the above-mentioned US Patent, as shown in FIG. 3, in the configuration of FIG. 1, the pre-processing unit 30 having the above-described function receives the receiving terminals 111 to 11N, the speakers 121 to 12N and the N channel echo canceller 221 It is added between ˜ 22M. A configuration example of this pre-processing unit 30 is shown in FIG. Here, the received signals from the receiving terminals 111 to 11N and the additional signals generated in the additional signal generation units 3011, 3012, ..., 301N are added by the adders 3021, 3022, ..., 302N to process the processed signals. Output x1 '(k), x2' (k), ..., xN '(k). 09-05-2019 3 When generating the additional signal, there are cases where the information of the reception signals x1 (k),..., XN (k) is used and cases where it is not used. By increasing the size of the additional signal, it is possible to improve the convergence characteristics of the adaptive filters 2211, ..., 221N. A similar approach is also shown in U.S. Patent No. 5,828,756. U.S. Patent Nos. 5,661,813; J. Benesty, DR R. Morgan, and M. M. Sondhi, "Abetter Understanding and an Improved Solution to the Problems of Stereophonic Acoustic Echo Cancellation", Proc. The preprocessing method proposed in ICASSP 97, vol. 1, pp. 303-306 (1997), etc. can be realized by the configuration shown in FIG. For example, for N channel signals xi (k) (i = 1, 2,..., N) at discrete time k, processing signals xi ′ (k) are processed by processing functions fi (i = 1, 2,. Xi '(k) = xi (k) even if it is a preprocessing unit that outputs (i = 1, 2, ..., N) as xi' (k) = fi [xi (k)] (1) Since it can be transformed into +) (fi [xi (k)]-xi (k)) (2), additional signal fi [xi (k)]-xi (k) is added to the original signal xi (k) It can be seen. [0009] SUMMARY OF THE INVENTION In order to improve the convergence characteristic of the adaptive filter in the above N channel echo canceller 221, 222,..., 22M, as shown in FIG. However, since the preprocessed signal is actually output from the speakers 121, 122, ..., 12N, if the preprocessing shown in FIG. 4 is performed, the magnitude of the additional signal is processed As compared with the previous reproduced sound, it is necessary to be limited within a range that does not cause auditory discomfort. For this reason, the improvement amount of the convergence characteristic of the adaptive filters 221 to 22N is also limited, and the improvement of the echo cancellation performance is also limited. [0010] Although the above example has been described with reference to echo cancellation in a multichannel call conference system, the principle of echo cancellation originally simulates the echo path from the speaker to the microphone in FIG. 1 in the echo canceller (ie impulse response of echo path) The estimation is intended to cancel the actual echo signal ym (k), and the reception signal does not necessarily have to be the reception signal from a remote place in the call conference system. For example, in a hall, a theater, a dome or the like provided with a loud sound system, this echo cancellation technology is used even in the case where an acoustic signal from a target sound source is picked up by a microphone and background sound emitted from a speaker is removed. Can be applied. Therefore, including the present invention, the reception signal in the following description may be a signal from any signal source as long as it is a reproduction electric signal to be supplied to the reproduction channel to be reproduced from 09-05-2019 4 the speaker. [0011] SUMMARY OF THE INVENTION An object of the present invention is to provide a new multichannel acoustic echo cancellation method for increasing the amount of improvement in echo cancellation performance even when the magnitude of a signal added by preprocessing is small. It is providing the device and the program recording medium. According to the present invention, it has N reproduction channels each including a speaker for outputting reproduction sound, and at least one pickup channel including N being an integer of 2 or more and including a microphone for collecting an acoustic signal. The multi-channel acoustic echo cancellation method in an acoustic system in which the N speakers and the microphone are disposed in a common sound field includes the following steps: (a) for reproduction respectively input to the N reproduction channels (B) adding the reproduction signals of the N reproduction channels and the addition signals for each reproduction channel to generate a processing signal of each reproduction channel; (c) reproducing the processed signals of the N reproduction channels from the speakers of the corresponding reproduction channel, and (d) selecting one of the N reproduction channels From each of the speakers, an acoustic echo that is looped and synthesized to the microphone of the pickup channel is collected and input as an acoustic echo signal to the pickup channel, (e) the N reproduction signals and the N Individual processing is performed on each additional signal to generate a pseudo echo that simulates the acoustic echo signal in the pickup channel, and acoustic echo cancellation is performed by subtracting the pseudo echo from the acoustic echo. [0012] According to the present invention, it has N reproduction channels each including a speaker for outputting reproduction sound, and at least one pickup channel including N being an integer of 2 or more and including a microphone for collecting an acoustic signal. In a multi-channel acoustic echo canceller in an acoustic system in which N speakers and a microphone are arranged in a common sound field, N generates an additional signal for reproduction signals respectively input to the N reproduction channels. N additional signal generation means, N processing signal generation means for adding the reproduction signals of the N reproduction channels and the addition signals of the N reproduction channels to each corresponding reproduction channel to generate processing signals, and N N above-mentioned speakers, each of which is provided in each of the reproduction channels, reproduces the processing signal of each reproduction channel, and outputs reproduction sound The microphones that collect acoustic echoes that are looped and synthesized from the N speakers and input them as the acoustic echo signals to the pickup channel, and the N reproduction signals and the N additional signals individually And 09-05-2019 5 processing means for generating a pseudo echo simulating the acoustic echo signal in the pickup channel, and canceling the acoustic echo signal by subtracting the pseudo echo from the acoustic echo signal. [0013] In the recording medium according to the present invention, the processing steps for carrying out the multi-channel acoustic echo cancellation method are recorded as a computer program. [0014] BEST MODE FOR CARRYING OUT THE INVENTION In the multi-channel acoustic echo cancellation method, the echo cancellation performance can be improved by a method in which an additional signal is added to the received signal, but the amount of improvement improves the additional signal due to auditory limitations. It is limited because it can not be enlarged. From another point of view of this problem, it can be said that there is a lack of sufficient information exchange between the pre-processing unit 30 and the N-channel echo cancelers 221,..., 22N in FIG. In the processing signal which is the sum of the reception signal and the small additional signal, the information of the additional signal is buried in the information of the reception signal. Therefore, in the conventional N-channel echo canceller, it is difficult to effectively extract and use the information of the additional signal from the input processed signal. [0015] Therefore, in the present invention, the information on the additional signal can be directly given to the echo canceller. FIG. 5 is a block diagram showing the basic configuration of the multichannel acoustic echo cancellation apparatus according to the present invention. Also in the device according to the present invention, additional signal generation units 3011 to 301N and adders 5011 to 501N are provided corresponding to the reception channels, respectively, and microphones 161 to 16M and an echo canceller 401 are provided corresponding to the respective transmission channels. To 40M, and the received signals x1 (k) to xN (k) and the additional signals a1 (k) to aN (k) are added by the adders 5011 to 501N, and the addition result 09-05-2019 6 (processed signal) x1 ' (k) to xN '(k) are applied to the speakers 121 to 12N in the same manner as the conventional configuration of FIG. [0016] A different point is the individually used echo canceller in which the reception signals x1 (k) to xN (k) before addition and the additional signals a1 (k) to aN (k) before addition are respectively provided corresponding to the transmission channels. 401 to 40M, and based on them, the echo signals y1 (k) to yM (k) of each transmission channel are estimated. That is, in the conventional FIG. 4, the reception signals x1 (k), x2 (k),..., XN (k) are added to the additional signals a1 (k), a2 (k),. After the addition, the addition result (ie, the preprocessed signal) of those additions is given to echo cancelers 221 to 22M of the transmission channel as shown in FIG. 3 to generate pseudo echo signals. As shown in FIG. 5, before the addition of the additional signal, the received signals x1 (k), x2 (k),..., XN (k) and the additional signal are sent to the individually used echo cancelers 401, 402,. a1 (k), a2 (k),..., aN (k) are separately input, and separately from them, received signals xi (k) (i = 1, 2,..., N) and additional signals ai (k) ) Is added by the adder 501i and reproduced from the speaker 12i. Therefore, even if the magnitude of the additional signal is limited due to a sense of hearing, the information on the additional signal embedded in the reception signal in the conventional configuration is used in the individually used echo canceller 401, 402, ..., 40M. Can be used directly to improve echo cancellation performance. [0017] As the nature of the additional signal suitable for the configuration shown in FIG. 5, it is required to take advantage of the ability to handle the reception signal xi (k) and the additional signal ai (k) individually. That is, if the additional signal ai (k) contains many components correlated with the incoming signal xi (k), even if the additional signal is processed individually, the influence of the incoming signal xi (k) on the processing result Is included. Therefore, the set of reception signals xi (k),..., XN (k) of all the reception channels and the set of additional signals a1 (k),. Is desirable. Therefore, with regard to the method of generating the additional signal, the number of received channels is generated as the additional signal since the number of low cross-correlation signals having low cross correlation with the received signals of all channels, that is, close to zero. [0018] 09-05-2019 7 Alternatively, when the individual additional signals have high correlation among the additional signal sets of all channels, in the conventional method, for the same reason as in the case where the correlation between the reception signals is high, Improvement is considered to be limited. Therefore, as a method of generating an additional signal, instead of the low cross correlation signal, signals having low cross correlation (near zero) with received signals of all channels and low cross correlation (near zero) are mutually low. The number of receiving channels is generated as a correlation signal, and these are allocated as additional signals. Next, a method of generating a low cross correlation additional signal will be described. Let the normal speech signal be x (k) and the expected value be [0020] It will be expressed as: The following equation E [x2 (k)] ¦ x (k)> 0 = E [x2 (k)] ¦ x (k) <0 (4) approximately holds for this expected value, so x (k) and The absolute value ¦ x (k) ¦ is approximately uncorrelated, that is, for any time difference n, approximately E [x (k) ¦ x (k−n) ¦] = 0 (5) It holds. Therefore, assuming that i = 1, 2,..., N are numbers assigned to the reception channels, the reception signal xi (k) of each reception channel and its absolute value signal ¦ xi (k) ¦ Also, if the received signals xi (k) and xj (k) of any two received channels are highly correlated, the absolute value signals ¦ xi (k) ¦ and ¦ xj (k) ¦ are also highly correlated with each other, It is considered that the reception signal xi (k) of any reception channel has low correlation with the absolute value signal ¦ xj (k) ¦ of any other reception channel. Therefore, αi ¦ xi (k) ¦ is generated with the adjustment coefficient for each receiving channel as αi, and this is used as a low cross correlation signal, that is, an additional signal. It is preferable to select the adjustment coefficient αi as large as possible within the range that the additional signal component in the reproduced sound from the speaker is not offensive in order to converge the adaptive filter coefficient in a short time. Additional Signal Generation Method (1) When the received signals x1 (k) to xN (k) have high correlation with each other, the low cross-correlation signals αi ¦ xi (k) ¦ Improvement is considered to be limited. Therefore, in each reception channel, the absolute value of the reception signal is taken, and the zero crossing at which the sign of the original reception signal changes is detected, and the above absolute value is synchronized with the detection point according to different rules for each reception channel. After giving the signal a positive or negative sign, the low cross-correlation signal is obtained by multiplying the adjustment factor. [0021] Here, as a method of giving a positive or negative sign to the absolute value signal, there are the 09-05-2019 8 following methods. In one receiving channel, the zero cross detection point is counted, and the sign given to the absolute value signal is exchanged at the zero cross point every predetermined count number C. In accordance with this rule, the sign given to the absolute value signal is inverted at the zero crossing point for each of the other different reception channels in the same way in the same way in different count values C. However, the count value C is an integer of 0 or 2 or more, and C = 0 means fixing the code. In this way, even when the received signals x1 (k) to xN (k) are highly correlated with each other, the obtained low cross-correlation signals are less correlated with each other, unlike the above case. [0022] 6A to 6D are examples in which the absolute value signal is given a sign according to the above rule. FIG. 6A shows an original signal, and the sign changes every zero crossing, so C = 1, and as shown in FIG. 6B, the sign of the absolute value signal does not change, and C = 0. Assuming that C = 2, as shown in FIG. 6C, the code changes every time zero crossing is performed twice, and when C = 3, the code changes every time zero crossing is performed three times as shown in FIG. 6D. It can be seen that the signals shown in FIGS. 6A to 6D are all uncorrelated with one another including the original signal. Hereinafter, the value of C will be referred to as a code switching cycle. Additional Signal Generation Method (2) A method of generating yet another low cross correlation signal will be described. That is, in each receiving channel, the absolute value signal of the receiving signal is taken, and the above-mentioned absolute value signal is multiplied by the adjustment coefficient which becomes nonzero for one receiving channel and zero for the other receiving channel, thereby adding low cross correlation. Get a signal. As a method of selecting a receiving channel giving a non-zero adjustment coefficient, there is a method of switching periodically or randomly with time, or a method of giving priority to a receiving channel having a large signal level. In this method, a valid additional signal is added to only one receiving channel at any time, so the time taken to generate an accurate pseudo echo is considered to be longer than in the above method (1). There is an advantage that it is possible to reduce the operation taking into account that the additional signal of the reception channel of the above is zero. [0023] Thus, according to the present invention, an additional signal to be added to each received signal in order to fluctuate or reduce the cross correlation between the received signals of multiple channels can be used separately for estimating the pseudo echo without adding it to the received signal. As a result, it is possible to generate a pseudo echo with high estimation accuracy by 09-05-2019 9 effectively using the uncorrelated component contained in the additional signal. Individually Used Echo Canceller FIG. 7 is an embodiment of the individually used echo canceller 40m (m = 1, 2,..., M) in FIG. In this configuration, received signals x1 (k) to xN (k) from the receiving terminals 111, 112,..., 11N are input to the received signal adaptive filters 4011, 4012,. Ru. In the present invention, the additional signal adaptive filters 4021 to 402N are provided corresponding to the respective reception channels, and the additional signals a1 (k) to aN (output terminals 181, 182, ..., 18N of the additional signal generation units 3011 to 301N are provided. k) are input to the additional signal adaptive filters 4021, 4022, ..., 402N, respectively. The sum of the outputs of the respective adaptive filters 4011, ..., 401N and 4021, ..., 402N is taken by the adder 403 to be a pseudo echo ym '(k), and an acoustic echo ym (k) collected by the microphone 16m. Then, this pseudo echo ym '(k) is subtracted by the subtraction circuit 404 to realize echo cancellation. Also, in this embodiment and the following embodiments, two different appropriate weights are applied to the error signal em (k) obtained by subtracting the pseudo echo ym '(k) from the acoustic echo ym (k). The coefficients w1 and w2 are given to generate two weighted error signals w1em (k) and w2em (k), the former is given to the adaptive filters 4011,..., 401N, and the latter is given to the adaptive filters 4021,. Adaptive filters 4011 to 401N and 4021 to 402N are based on weighted error signals w1em (k) and w2em (k) and input signals x1 (k) to xN (k) and a1 (k) to aN (k). For the currently set filter coefficients, calculate the filter coefficient vector that minimizes the error signal em (k) by the well-known NLMS algorithm etc., thereby updating each filter coefficient of the adaptive filter, and the next input Prepare for The specific calculation method of the filter coefficient update will be described later. [0024] The weighting for the error signal fed back to each of the reception signal adaptive filters 4011, ..., 401N and the additional signal adaptive filters 4021, ..., 402N is, for example, small for each of the reception signals with large power. A weighting factor w1 is given, and a large weighting factor w2 is given to each of the above-mentioned small-power additional signals. As described above, in the pseudo echo generation of the individually used echo canceller shown in FIG. 7, there is an advantage that the precision of the pseudo echo can be controlled by processing the information on the reception signal and the information on the additional signal with different weightings. . In practice, when reproducing the processing signal in which the additional signal is added to the receiving signal in FIG. 5 from the speaker, it is necessary to adjust the range in which the additional signal has an effect on the audibility. Often small. In such a case, information on a small additional signal can be effectively used by the above weighting process. However, as a basic configuration of the present invention, w1 = w2 in FIG. That is, the weighting unit 411 may be omitted, and the same em (k) may be given to the adaptive filters 4011 to 401N and 4021 to 402N. The same can be said for all the other modified embodiments below. Modification 1 of Echo Canceller FIG. 8 shows an alternative to the echo canceller of FIG. 7 09-05-2019 10 applied to the individually used echo canceller 40m (m = 1,..., M) in FIG. The embodiment of FIG. 7 shows the case where the adaptive filters 4011 to 401N for the received signal and the adaptive filters 4021 to 402N for the additional signal are separately provided and processed separately in each N channel echo canceller 40m. As shown in FIG. 8, N additional signals a1 (k) to aN (k) and received signals x1 (k) to xN (k) are subjected to another process and then combined to obtain N combined signals x. "1 (k) to x" N (k) may be processed by N adaptive filters 4011 to 401N. [0025] That is, as shown in FIG. 8, the received signals x1 (k) to xN (k) are multiplied by gain coefficients g11 to g1N by multipliers 4121 to 412N, respectively, to be g11x1 (k) to g1NxN (k). The additional signals a1 (k) to aN (k) are multiplied by gain coefficients g21 to g2N by multipliers 4101 to 410N, respectively, to be g21a1 (k) to g2NaN (k). The gain coefficients g21 to g2N for the additional signal are larger than the gain coefficients g11 to g1N for the reception signal of the corresponding reproduction channel. These multiplication results are added by the adders 4121 to 412N for each corresponding reproduction channel, and N combined processed signals {g11x1 (k) + g21a1 (k)}, {g12x2 (k) + g22a2 (k)}, , And {G1NxN (k) + g2NxN (k)} are respectively input to N adaptive filters 4011 to 401N. [0026] The sum of the outputs of the adaptive filters 4011 to 401N is taken by the adder 403, and the sum is given to the subtractor 404 as a pseudo echo y'm (k), and is subtracted from the acoustic echo signal ym (k). k) generate. The error em (k) is fed back to the adaptive filters 4011 to 401N, and the combined processed signal {g11x1 (k) + g21a1 (k)}, {g12x2 (k) + g22a2 from the error em (k) and the adders 4121 to 412N. The filter coefficients of the adaptive filters 4011 to 401N are updated based on (k)},..., {g1NxN (k) + g2NxN (k)}. [0027] What is important in the embodiment of FIG. 8 is that the additional signal an (k) and the reception signal xn (n) as components of the processing signal x'n (k) reproduced by each of the speakers 12n (n = 1,..., N). The level ratio of the additional signal component g2nan (k) and the reception signal component g1nxn (k) in each combined processed signal is made larger than the 09-05-2019 11 level ratio k). That is, the additional signal component an (k) in the reproduced sound from the speaker 12n is reduced to an extent that it does not become offensive, while the additional signal component uncorrelated in the synthetic processing signal {g1nxn (k) + g2nan (k)} The filter coefficient of the adaptive filter 401 n can be converged in a short time by sufficiently increasing the level of the signal component g 2 nan (k). Second Embodiment of Echo Canceller FIG. 9 shows another embodiment of each individually used echo canceller 40m shown in FIG. 5 in place of that of FIG. In the same way as shown in FIG. 7, for each transmission channel, reception signal adaptive filters 4011, 4012,..., 401N corresponding to all reception channels and additional signal adaptive filters 4021, 4022,. On the other hand, respective reception signals and respective additional signals respectively corresponding thereto are input, and a total sum y'm (k) of the outputs of all the adaptive filters 4011 to 401N and 4021 to 402N is obtained by the adder 403. The output y'm (k) of the adder 403 is subtracted from the acoustic echo ym (k) collected by the microphone to obtain an error signal em (k). Given w 2 to generate weighted error signals w 1 em (k) and w 2 em (k), give the former to the adaptive filters 4011,..., 401 N, and the latter to the adaptive filters 402 1,. Adaptive filters 4011 to 401N and 4021 to 402N update the filter coefficients by the NLMS algorithm or the like based on the given signals w1em (k) and w2em (k), and prepare for the next input. In this embodiment, the error signal em (k) is only used to determine the filter coefficients of the adaptive filters 4011 to 401N and 4021 to 402N and is not output as an echo cancellation result. [0028] In this embodiment, adders 4061 to 406N that add received signals x1 (k) to xN (k) and additional signals a1 (k) to aN (k) for each corresponding received channel, and those adders 4061 to 406N. An echo canceling filter 4051 to 405 N which respectively gives the addition result of 406 N, and an adder 407 which adds the outputs of the echo canceling filters 4051 to 405 N to obtain a pseudo echo signal y "m (k), an echo signal ym ( There is further provided a subtractor 408 which cancels the echo by subtracting the pseudo echo signal y "m (k) from k) and uses the residual as the output of the transmission channel. The adders 4061 to 406N add the reception signals x1 (k) to xN (k) of the corresponding reception channels and the additional signals a1 (k) to aN (k), respectively, and the adders 5011 to 501N in FIG. Are the same as the processing signals x'1 (k) to x'N (k) which are the addition results of Therefore, the adders 4061 to 406N are not provided in the individual use type echo cancellers 401 to 40M, and the processing signals x'1 (k) to x'N (k) which are the outputs of the adders 5011 to 501N in FIG. It may be provided to the echo canceling filters 4051 to 405N of the echo canceller 40m (m = 1,..., M). The same can be said for the examples described below. [0029] 09-05-2019 12 Usually, the correlation between the additional signals a1 (k) to aN (k) is smaller than the correlation between the reception signals x1 (k) to xN (k). It is expected to converge in a short time with higher accuracy than the -401N filter coefficient. Therefore, in this embodiment, for example, when the power of the error signal em (k) becomes sufficiently smaller than the power of the echo signal ym (k), it is determined that the filter coefficients of the adaptive filters 4021 to 402N have converged to some extent, The filter coefficients of the adaptive filters 4021 to 402N are transferred to the echo cancellation filters 4051 to 405N and used. [0030] For that purpose, a short time average power calculation unit 413 and a transfer control unit 414 are provided. The short-time average power calculation unit 413 receives the error signal em (k) and the echo signal ym (k), and calculates, for example, average values Pem (k) and Pym (k) of power over a predetermined length within one frame period. . These values are given to the transfer control unit 414, and the transfer control unit 414 obtains the ratio Pem (k) / Pym (k) of these values, and the ratio of the filter coefficient is determined in advance as a transfer condition (for example, If it is satisfied, the transfer control signal TC is applied to the adaptive filters 4021 to 402N to transfer the filter coefficients of the adaptive filters 4021 to 402N to the echo cancellation filters 4051 to 405N. Transfer coefficients. From then on, the ratio Pem (k) / Pym (k) is always calculated, and the filter coefficients of the adaptive filters 4021 to 402N are transferred to the echo cancellation filters 4051 to 405N only when the aforementioned transfer conditions are satisfied. If necessary, it may be added as a necessary condition that the reception signal level as the transfer condition, for example, the sum of short-time average power of all the reception signals is a predetermined value or more. [0031] The outputs of these echo cancellation filters 4051,..., 405N are added by an adder 407 to obtain the sum of them as a pseudo echo y "m (k). By subtracting the pseudo echo y "m (k) from the acoustic echo ym (k) by a subtractor 408, an echo canceled signal is obtained. Variation 3 of Echo Canceller FIG. 10 shows another variation of the individually used echo canceller 40m in FIG. As described above, in the embodiment of FIG. 9, the pseudo echo signal generated by the echo cancellation filter by transferring the coefficient of the additional signal adaptive filter which is expected to be rapidly converged to the echo cancellation filter. As compared with the embodiment of FIG. 7, y ′ ′ m (k) can be brought closer to the echo signal ym (k) in a shorter 09-05-2019 13 time, so that the effect of echo cancellation can be expressed in a shorter time. The filter coefficients of the additional signal adaptive filters 4021 to 402N are more accurate than the filter coefficients of the reception signal adaptive filters 4011 to 401N at the same elapsed time point k, and the true echo impulse response (vector) h1 (k), h2 (k), ..., hN (k) (approximate the impulse response vector, that is, the coefficient vector in the following description, not in bold but in bold in the formula). It is estimated to be. In other words, the filter coefficients of the adaptive filters 4011 to 401N and 4021 to 402N are obtained by the adaptive algorithm based on the sum em '(k) of the sum of these outputs y'm (k) and the echo signal ym (k) Therefore, it can be considered that the filter coefficients of the reception signal adaptive filters 4011 to 401N contribute to the error of the filter coefficients of the additional signal adaptive filters 4021 to 402N currently obtained. Therefore, in the modified embodiment of FIG. 10, the additional filter adaptive filter coefficients with high accuracy are also transferred to the reception signal adaptive filter for use. [0032] The echo canceller 40m of FIG. 11 is provided corresponding to each transmission channel as shown in FIG. 5, and as in the case of FIG. 9, an adaptive filter 4011 individually provided for each reception signal and each additional signal. , 4012,..., 401N and 4021, 4022,..., 402N, the corresponding reception signals x1 (k) to xN (k) and the additional signals a1 (k) to aN (k) are input, respectively. The sum y 'm (k) of the filter outputs is obtained. From the acoustic echo ym (k) collected by the microphone, the sum y'm (k) of the output of this adaptive filter is subtracted to obtain an error signal em (k). This error signal em (k) is weighted by weighting factors w1 and w2 by weighting section 411 to generate error signals w1em (k) and w2em (k), which are fed back to adaptive filters 4011 to 401N and 4021 to 402N, respectively. Update the filter and prepare for the next input. [0033] In the actual echo cancellation, the coefficients of the adaptive filter for the additional signal are transferred to the corresponding echo cancellation filters 4031, 4032,..., 403N, and these echo cancellation filters receive the reception signal and the additional signal for each reception channel. The sum is input, the sum of the echo cancellation filters is obtained as a pseudo echo y "m (k), and the echo cancellation is realized by subtracting this pseudo echo y" m (k) from the acoustic echo ym (k) . The coefficients of the adaptive filter for the additional signal are transferred to the corresponding echo cancellation filters 4051, 4052, ..., 405N, and simultaneously with the adaptive filters 4011, 4012, ..., 401N provided for the respective 09-05-2019 14 reception signals. Can be used to improve the overall accuracy of the adaptive filter. [0034] The conditions for coefficient transfer may be the same as in the embodiment of FIG. As in the case of FIG. 9, based on the power Pem (k) of the error signal calculated by the short-time average power calculator 413 and the power Pym (k) of the acoustic echo, the transfer controller 414 determines whether the transfer condition is satisfied. If satisfied, the transfer control signal TC is applied to the adaptive filters 4021 to 402N, and the filter coefficients are transferred to both of the adaptive filters 4011 to 401N and 4051 to 405N. In this modified embodiment, when receiving the transfer of the filter coefficients, the reception signal adaptive filters 4011 to 401N are newly updated from the filter coefficients. Echo Canceller Modification 4 FIG. 11 shows still another modification of the individually used echo canceller shown in FIG. In FIG. 9 described above, in general, the correlation between the reception signals x1 (k) to xN (k) is large, so the coefficients of the adaptive filters 4021 to 402N to which the low correlation additional signal is given are the reception signal adaptive filters 4011 to 401N. The coefficients of the additional signal adaptive filters 4021 to 402N are transferred to the echo cancellation filters 4051 to 405N on the premise that the filter coefficients are converged more rapidly and with higher precision than the filter coefficients of the above. However, the reception signals x1 (k) to xN (k) are not always always highly correlated. When signals from a plurality of completely different sources are given as multi-channel reception signals, the correlation between the reception signals may be sufficiently small. In that case, it is expected that the coefficients of the reception signal adaptive filter converge at high speed and can be obtained with high accuracy. Therefore, in the modified embodiment of FIG. 11, the maximum correlation value between the reception signals x1 (k) to xN (k) is calculated, and if the maximum correlation value is larger than a predetermined value, addition is performed as in the embodiment of FIG. The coefficients of the signal adaptive filter are transferred to the echo cancellation filter, and if less than a predetermined value, the coefficients of the reception signal adaptive filter are transferred to the echo cancellation filter. [0035] The echo canceller 40m of FIG. 11 is provided for each of the transmission channels as shown in FIG. 5, and the reception signals x1 (k) to xN (k) and additional signals a1 (k) to aN are provided similarly to FIG. (6) Input the corresponding received signals x1 (k) to xN (k) and additional signals a1 (k) to aN (k) to the adaptive filters 4011 to 401N and 4021 to 402N individually provided for (k). The adder 403 obtains the sum y'm (k) of the outputs of all the adaptive filters. 09-05-2019 15 The sum y'm (k) of the output of this adaptive filter is subtracted from the acoustic echo ym (k) collected by the microphone to obtain an error signal em (k), and this error signal em (k) is weighted by the weighting unit 411. The signals w1em (k) and w2em (k) generated with the weighting factors w1 and w2 are fed back to the adaptive filters 4011 to 401N and 4021 to 402N, the coefficients of these adaptive filters are updated, and the signals are prepared for the next input. [0036] As a difference from the configuration of FIG. 9, in the actual echo cancellation, the correlation determination unit 430 obtains the correlation between the reception signals x1 (k) to xN (k) for all combinations, and If the value is larger than the predetermined value, the coefficients of the adaptive filters 4021 to 402N to which the additional signals a1 (k) to aN (k) are input are input to the processed signals x'1 (k) to the corresponding receiving channels. It transfers to the echo cancellation filter which receives x'N (k), and when the maximum correlation value between the above-mentioned receiving signals is smaller than a predetermined value, the adaptive filters 4011 to 401 N receiving the above-mentioned receiving signals as input A transfer selection control signal TS is applied to the transfer control unit 414 so as to transfer the coefficients to the echo cancellation filters 4051 to 405N to which the processing signals x'1 (k) to x'N (k) are input. The transfer control unit 414 transfers the transfer control signal TC2 to the adaptive filters 4021 to 402N when transferring the coefficients of the additional signal adaptive filters 4021 to 402N according to the transfer selection control signal TS when the transfer conditions are satisfied as described above. When the coefficients of the reception signal adaptive filters 4011 to 401N are transferred, the transfer control signal TC1 is applied to the adaptive filters 4011 to 401N. Processing for the echo cancellation filters 4051 to 405N in which the transferred filter coefficients are set is the sum of the reception signals x1 (k) to xN (k) and the additional signals a1 (k) to aN (k) for each reception channel Signals x'1 (k) to x'N (k) are input, and the sum y "m (k) of the outputs of the echo cancellation filters 4051 to 405N is obtained as a pseudo echo, and from the acoustic echo ym (k), Echo cancellation is realized by subtracting the pseudo echo y "m (k). [0037] In the method of FIG. 10, when the correlation between the reception signals x1 (k) to xN (k) is small, the reception signal has a higher level than the additional signal, so the accuracy of the adaptive filter for the reception signal is better. Are trying to improve the performance. Echo Canceller Modification 5 FIG. 12 shows another configuration of the individually used echo 09-05-2019 16 canceller. In this configuration, similarly to the configuration of FIG. 9, each of the reception signals x1 (k) to xN (k) corresponding to the adaptive filters 4011 to 401N and 4021 to 402N individually provided for the reception signals and the additional signals, respectively. And each additional signal a1 (k) to aN (k) to obtain the sum y "m (k) of the outputs of all the adaptive filters, and this adaptation from the acoustic echo ym (k) collected by the microphone The sum y'm (k) of the filter outputs is subtracted to obtain an error signal em (k). The error signal em (k) is weighted by coefficients w1 and w2 by the weighting unit 411 to generate the signals w1em (k) and w2em (k), which are fed back to the adaptive filters 4011 to 401N and 4021 to 402N. Update the coefficients and prepare for the next input. [0038] As a difference from the configuration of FIG. 9, in the actual echo cancellation, the correlation between the above-mentioned reception signals x1 (k) to xN (k) is obtained in the correlation determination unit 480 as in the embodiment of FIG. The echo cancellation filters 4051 to 405N receive the processed signal as input for the corresponding reception channels for the coefficients of the adaptive filters 4021 to 402N to which the additional signal is input, and the reception signal Are transferred to the respective adaptive filters 4011 to 401N with the input as the input, and when the correlation between the reception signals is smaller than a predetermined value, the coefficients of the respective adaptive filters The transfer control unit 414 is supplied with transfer selection signals TS for controlling transfer to the echo cancellation filters 4051 to 405N to which the processing signal is input and the adaptive filters 4021 to 402N to which the additional signal is input. [0039] When the transfer control unit 414 transfers the coefficients of the additional signal adaptive filters 4021 to 402N according to the given transfer selection signal TS when the transfer conditions are satisfied, the transfer control signal TC2 is transferred to the adaptive filters 4021 to 402N. When the coefficients of the reception signal filters 4011 to 401N are transferred, the transfer control signal TC1 is applied to the adaptive filters 4011 to 401N. Sum of reception signals x1 (k) to xN (k) of reception channels corresponding to the filters for echo cancellation 4051 to 405N and additional signals a1 (k) to aN (k) (that is, processed signals) x'1 (k) .About.x'N (k) are input, and the sum y "m (k) of the outputs of the echo cancellation filters 4051 to 405N is obtained as a pseudo echo. Echo cancellation is realized by subtracting this pseudo echo y ′ ′ m (k) from the acoustic echo ym (k). This embodiment not only has the advantages of both FIG. 10 and FIG. 11, but also enables transfer of filter coefficients from the 09-05-2019 17 reception signal adaptive filter to the additional signal adaptive filter to obtain more accurate filter coefficients. it can. [0040] FIG. 13 shows a configuration example of the correlation determination unit 430 in the embodiments of FIGS. The correlation determination unit 430 evaluates the cross correlation between the reception signals of the respective channels with respect to the sample points for each frame width divided into the number of taps L of the adaptive filter. The received signals x1 (k) to xN (k) are always, for example, two frames long from the current point k to the past (ie, time points k, k-1, ..., k-L + 1, kL, ..., k-2L + 1) A minute number of signal samples are held in the buffer 431. The frame cutout unit 432 includes L samples xn (k), xn (k-1),..., Xn (k-L + 1) consecutive from the reception signal in the buffer 431 in the past for each reception channel. The reception signal sequence is cut out as a vector x n (k) (n = 1, 2,..., N). Although the reception signal vector is shown in bold in the following equation, it can be distinguished by those skilled in the art, so in the following description, the reception signal vector is written in a standard font, not bold. The inner product calculation unit 433 selects two channels (assuming n = i and n = j) to be evaluated among all the channels, and calculates the inner product of their signal sequence vectors, for example, xi (k) and xj (k). First calculate. The normalization unit 434 divides this inner product result xiT (k) .xj (k) by the magnitudes of the two signal sequence vectors to be evaluated, and the cross correlation evaluation amount EC, for example, [0042] To obtain However, with the equation (6) as it is, when the signals having high correlation with each other at mutually shifted positions on the time axis, appropriate evaluation amounts can not be obtained. Therefore, the time difference can be calculated by calculating the cross correlation evaluation amount EC each time the time k of one vector, for example, xj (k) is sequentially shifted over k−1, k−2,. Evaluate signals with high correlation. As described above, the correlation evaluation unit 435 compares the cross correlation evaluation amounts EC calculated for all combinations of received signals (i, j) in all channels, and the maximum value among them is used as the entire system. Adopted as an evaluation amount of When the cross-correlation evaluation amount EC between at least one set of reception signals is larger than a predetermined value, the transfer selection unit 436 selects the coefficients of the adaptive filters 4021 to 402N for the additional signals as the adaptive filters for the reception signals. It is determined that convergence is performed with higher accuracy than 4011 to 401N, and the adaptive filter coefficients for each additional signal are transferred to the other filters 4011 to 09-05-2019 18 401N and 4051 to 405N, and if there is no correlation evaluation amount larger than a predetermined value, reception is received. A transfer selection signal TS for transferring the coefficients of the signal adaptive filters 4011 to 401N to the filters 4021 to 402N and 4051 to 405N is supplied to the transfer control unit 414. The multi-channel acoustic echo canceler according to the present invention as described above comprises received signals x1 (k) to xN (k) given to each part constituting it and acoustic echo signal y1 (k) from a microphone ) To yM (k) may be realized as data processing by a computer, for example. In that case, the processing of each unit shown in the above-described embodiment is described as a program, stored in advance in a recording medium, and the program read out from the recording medium at the time of use is executed by a computer. An example of such a configuration is shown in FIG. A computer 100 operating as an acoustic echo canceler shown in FIG. 14 is a computer having a very general configuration, and a CPU (central processing unit) 110, RAM 120, hard disk 130, interface 140, etc. Is configured. A program for executing echo cancellation according to the present invention is stored in advance in, for example, the hard disk 130, and the program is read into the RAM 120 at the time of operation, and the CPU 110 executes processing in accordance with the program. The received signals x1 (k) to xN (k) and the echo signals y1 (k) to yM (k) from the microphone are taken in via the I / O interface unit 140, subjected to the above-described echo cancellation processing, and subjected to echo cancellation The residual signals e1 (k) to eM (k) are outputted through the I / O interface 140. The program for echo cancellation may be recorded on an arbitrary recording medium 170 as the external storage device 170, and read from there onto the RAM 120 by the driver 160 of the storage device for execution. [0043] Implementation Example in the Case of Two Channels Here, as an example of FIG. 9 representing the embodiment of the multi-channel echo canceller of the present invention described above, generation of additional signal as a system of two receiving channels and one transmitting channel, The operation of the adaptive filter and error weighting will be described more specifically with reference to FIG. [0044] In FIG. 15, parts corresponding to those in FIGS. 5 and 9 are given the same reference numerals. [Generation of Addition Signal] An addition signal is generated for the two-channel reception 09-05-2019 19 signal x1 (k), x2 (k). When a code switching cycle C is given, a code coefficient giving a code inversion at each count C of zero cross points is represented by .sigma.c. It is σ C = 1, -1. First, for the reception channel 1, the code is fixed with the code switching cycle C = 0, and the adjustment coefficient is α1 to obtain the additional signal α1 ¦ x1 (k) ¦. Also, for the receiving channel 2, as the code switching cycle C = 2, the value of the code coefficient σ C is alternately switched between 1 and -1 every two zero cross detection points of x 2 (k) to adjust the adjustment coefficient Let .alpha. @ 2 be the additional signal .alpha. @ 2 .sigma.C.vertline.x @ 2 (k) .vertline. Here, in the case of the code switching cycle C = 2, instead of counting the number of zero crossing points in the timing detection of the above code switching, the time at which the code of x2 (k) changes from positive to negative or It is also possible to switch the code synchronously with the time when it changes from negative to positive. "Operation of adaptive filter" In describing the operation of the adaptive filter, the signal is vectorized. That is, in the following description, the reception signal vector is expressed as x 1 (k), x 2 (k), and the additional signal vector α 1 x −1 (k), α 2 x − 2 (k). However, in the formula, the vector is shown in bold. Here, x1 (k) = [x1 (k), x1 (k-1),..., X1 (k-L + 1)] T (7) x2 (k) = [x2 (k), x2 (k) -1), ..., x2 (k-L + 1)] T (8) x-1 (k) = [¦ x1 (k) ¦, ¦ x1 (k-1) ¦, ..., ¦ x1 (k- L + 1) ¦] T (9) x-2 (k) = [σC ¦ x2 (k) ¦, σC ¦ x2 (k-1) ¦, ..., σC ¦ x2 (k-L + 1) ¦] T (10), where T represents the transpose of the vector. L is the number of taps of the adaptive filter, and the coefficient vectors of the adaptive filters 4011 and 4012 to which x1 (k) and x2 (k) are input are respectively h ^ 1 (k) and h ^ 2 (k), and α1x The coefficient vectors of the adaptive filters 4021 and 4022 to which −1 (k) and α2x−2 (k) are input are h−1 (k) and h−2 (k), respectively. Also, an impulse response, which is a transfer characteristic between two speakers and microphones, is modeled as a true acoustic echo path vector h1 (k), h2 (k) of length L and used in the following discussion. [0045] First, the acoustic echo y (k) that gets around from the two speakers to the microphone, [0047] It can be expressed as: Adaptive filters 4011, 4012, 4021 and 4022 are used to simulate this acoustic echo y ^ (k). [0049] 09-05-2019 20 Calculate: From the comparison of the equations (12) and (13), the coefficient vector of each adaptive filter is h ^ 1 (k) → h1 (k) (14) h ^ 2 (k) → h2 (k) (15) h- It should converge with 1 (k) → h1 (k) (16) h-2 (k) → h2 (k) (17), so ideally, h-1 (k) = h ^ 1 ( k), h-2 (k) = h ^ 2 (k). However, in many cases, there is a high correlation between x1 (k) and x2 (k), and as in the conventional method, the mutual channels affect each other, so h ^ 1 (k), h ^ 2 The convergence of (k) stagnates. On the other hand, since α1x-1T (k) and α2x-2T (k) have low correlation with each other and also have low correlation with x1 (k) and x2 (k), h-1 (k), h The convergence of -2 (k) is not affected by the signals of other channels. In other words, it is considered that at least the coefficients of h-1 (k) and h-2 (k) converge with high accuracy. Therefore, even if y '(k) is used as a pseudo echo, some performance improvement can be expected, but the effect of h ^ 1 (k) and h ^ 2 (k) does not affect the generation of the pseudo echo, Accurate h-1 (k) and h-2 (k) are transferred as coefficient vectors to the echo cancellation filters 4051 and 4052, respectively, and adders 4061 and 4062 are respectively transmitted to the echo cancellation filters 4051 and 4052. By inputting x1 (k) + α1x-1 (k) and x2 (k) + α2x-2 (k) from 4062, respectively, and generating the pseudo echo from the adder 407 as the sum of their outputs, The accuracy of the echo can be increased. In the following, h-1 (k) and h-2 (k) are first simulated with respect to true impulse responses h1 (k) and h2 (k) of echo paths 1511 and 1512 from the speakers 121 and 122 to the microphone 161, respectively. It is called echo path impulse response, and h ^ 1 (k) and h ^ 2 (k) are called second pseudo echo path impulse response. Also, for these true echo paths 1511 and 1512, adaptive filters 4011 and 4012 are called first pseudo echo paths, and adaptive filters 4021 and 4022 are called second pseudo echo paths. Error Weighting Method of weighting differently by the weighting unit 414 in feeding back the error signal e (k) between the acoustic echo y (k) and the adaptive filter output y ^ (k) for updating the coefficients of each adaptive filter Describe. [0050] First, each adaptive filter coefficient vector h ^ 1 (k), h ^ 2 (k), h-1 (k), h-2 (k) is expressed by the following equation using the NLMS algorithm [0052] Suppose that it is updated to Here, the adjustment coefficient is α1 = α2 = α. Further, e (k) = y (k) −y ′ (k), and μ is a parameter called a step size. From the left on both sides, with μ = 1 for equation (18) 09-05-2019 21 [0054] By multiplying y (k) = y '(k) + e (k) / (1 + α2) + α2 e (k) / (1 + α2) = y' (k) + e (k) (20) It becomes. That is, if the input signal at time k is input again to the updated adaptive filter, the error signal e (k) is compensated, and the sum of the outputs is equal to y (k). Here, the second and third terms on the middle side of equation (20) are the sum of the inner products when the second term on the right side of equation (18) is multiplied by equation (19) from the left [0056] (20) is the adaptive filter coefficient vector h ^ 1 (k + 1), h ^ 2 for x1 (k), x2 (k). The compensation term according to (k + 1), and the third term of the middle side is the adaptive filter coefficient vector h-1 (k), h-2 (for the additional signals α1x-1 (k), α2x-2 (k) It turns out that it is the compensation part by k). Normally, the value of α is small, for example, about α = 0.2. Therefore, equation (18) is more susceptible to the correlation of the reception signals than h−1 (k + 1) and h−2 (k + 1) which are expected to have high convergence accuracy. It is understood that updating is performed with emphasis on (k + 1) and h ^ 2 (k + 1). [0057] Therefore, the weighting unit 411 performs e in the update of h ^ 1 (k + 1), h ^ 2 (k + 1) and the update of h-1 (k + 1), h-2 (k + 1). (k) are respectively multiplied by different weighting factors w1 and w2. That is, the adaptive filter update equation [0060] 【0060】とする。 Thus, e (k) = (1 / (1 + α2)) w1 e (k) + (α2 / (1 + α2)) w2 e (k) (24) is obtained. Then, if, for example, w1 = (1 + α2) / 2 (25) w2 = (1 + α2) / (2α2) (26), equation (24) is e (k) = (1/2) e (k) + (1/2) e (k) (27), and the adaptive filter coefficient vector h ^ 1 (k + 1), h ^ 2 for x1 (k), x2 (k) of the first term on the right side Adaptive filter coefficient vector h-1 (k + 1), h-2 (k +) for the compensation by (k + 1) and the additional signal α1x-1 (k), α2x-2 (k) of the second term on the right side The compensation amount according to 1) is equal. Further, since w1 and w2 in the equations (25) and (26) are w1: w2 = 1: (1 / α2), the power of x1 (k) and x2 (k), α1x-1 (k), respectively. , Α 2 x − 2 (k) are weighted in inverse proportion to the power. 09-05-2019 22 [0061] When α is too small, if w1 and w2 are selected as in the equations (25) and (26), w2 may become very large and the calculation may become unstable. Therefore, it is preferable to introduce a relaxation coefficient β and set the update formula of the adaptive filter as the following equation. [0064] Equations (28) and (29) show computer simulation results in the case where the adaptive filter is updated, in the case where the input is Gaussian white noise and for the case of male speech in FIGS. 16A and 16B. Curve (a) represents the normalized squared error of h ^ 1 (k), h ^ 2 (k) according to the invention with respect to h1 (k), h2 (k), curve (b) is h- according to the invention Represents a normalized squared error of 1 (k), h-2 (k). Curve (c) is an adaptive filter h ^ 1 (h) for h1 (k) and h2 (k) in the conventional method when x1 (k) + α1x-1 (k) and x2 (k) + α2x-2 (k) are input. k), the normalized squared error of h 2 (k). The parameters were α = 0.2, β = 0.7, μ = 0.5, the adaptive filter length was 1000 taps each, and noise was added to the acoustic echo so that the SN ratio was 30 dB. From this, it can be seen that the convergence performance of h-1 (k) and h-2 (k) for additional signals is excellent. [0065] Although the embodiments of the present invention described above have described echo cancellation in the teleconference system as an example, as described above, the principle of the present invention is that the reproduction from the speaker superimposed on the target acoustic signal picked up by the microphone It is effective in removing sound. Therefore, in an acoustic system in which a plurality of reproduction channels each including a speaker and at least one pickup channel including a microphone for picking up a target sound are provided in a common sound field, the speaker picked up by the microphone The present invention can be applied to any system for the purpose of erasing reproduced sound. [0066] According to the multi-channel acoustic echo cancellation method, the echo cancellation performance can be improved by the previously proposed method of applying the additional signal to the reception signal, but the additional signal can be made larger due to the auditory restriction. Also, since the processing signal which is the sum of the reception signal and the additional signal is used in the generation of the pseudo echo for echo cancellation, the important information contained in the additional signal is buried in the reception signal, and the echo cancellation performance The amount of improvement was limited. [0067] According to the method of the present invention, first, after generating an appropriate additional signal, instead of using the above processing signal in the generation of a pseudo echo for echo cancellation, the receiving signal and the additional signal are processed separately. The important information contained in the additional signal can be easily used. Thereby, the pseudo 09-05-2019 23 echo for echo cancellation can be generated with high accuracy. Therefore, the echo cancellation performance can be improved as compared with the conventional method. 09-05-2019 24
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