Method and apparatus for multi-channel acoustic echo cancellation
First Claim
1. An N-channel echo cancellation method comprising the steps of:
- (a) radiating an input signal xn (k) of each channel n, (n=1, . . . N) as an acoustic signal by a loudspeaker of said each channel, said input signal being inputted as a sample every discrete time k and N being an integer equal to or greater than 2;
(b) picking up, by one microphone, said N acoustic signals propagating thereto over N echo paths from said N loudspeaker to obtain an echo y(k);
(c) obtaining a combined input signal vector x(k)=[x1T (k), x2T (k), . . . , xNT (k)]T by combining input signal vectors xn (k) of said N channels, each composed of an input signal sequences xn (k), xn (k-1), . . . , xn (k-Ln +1) counted back to time Ln -1 from said discrete time k in said each channel n;
(d) generating an estimated echo y(k) by inputting said combined input signal vector x(k) into a combined estimated echo path which has a combined estimated impulse response vector h(k) obtained by combining estimated impulse response vectors hn (k) (n=1, . . . , N, of N estimated echo paths corresponding to said N echo paths, each of said N estimated echo paths having Ln taps;
(e) obtaining a residual echo e(k) by subtracting said estimated echo signal y(k) from said echo y(k) obtained in said one microphone;
(f) extracting a variation in the cross-correlation between said input signals of said N channels on the basis of said residual echo e(k) and said combined input signal vector x(k);
(g) generating an adjustment vector v(k) on the basis of said cross-correlation variation;
(h) adjusting said combined estimated impulse response vector h(k) of said combined estimated echo path by said adjustment vector v(k) to obtain a combined estimated impulse vector h(k+1) for use at the next time k+1; and
(i) repeating said steps (a) to (h) upon each increment of time k.
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Abstract
A variation in the cross-correlation between current received signals of different channels is extracted which corresponds to the cross-correlation between previous received signals, and the extracted variation is used as an adjustment vector to iteratively adjust the estimation of the impulse response of each echo path. Furthermore, by additionally providing a function of actively varying the cross-correlation between the received signals to such an extent as not to produce a jarring noise, it is possible to reconstruct acoustic signals by individual loudspeakers and utilize received signal added with the cross-correlation variation to obtain the adjustment vector for an estimated echo path vector.
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Citations
21 Claims
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1. An N-channel echo cancellation method comprising the steps of:
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(a) radiating an input signal xn (k) of each channel n, (n=1, . . . N) as an acoustic signal by a loudspeaker of said each channel, said input signal being inputted as a sample every discrete time k and N being an integer equal to or greater than 2; (b) picking up, by one microphone, said N acoustic signals propagating thereto over N echo paths from said N loudspeaker to obtain an echo y(k); (c) obtaining a combined input signal vector x(k)=[x1T (k), x2T (k), . . . , xNT (k)]T by combining input signal vectors xn (k) of said N channels, each composed of an input signal sequences xn (k), xn (k-1), . . . , xn (k-Ln +1) counted back to time Ln -1 from said discrete time k in said each channel n; (d) generating an estimated echo y(k) by inputting said combined input signal vector x(k) into a combined estimated echo path which has a combined estimated impulse response vector h(k) obtained by combining estimated impulse response vectors hn (k) (n=1, . . . , N, of N estimated echo paths corresponding to said N echo paths, each of said N estimated echo paths having Ln taps; (e) obtaining a residual echo e(k) by subtracting said estimated echo signal y(k) from said echo y(k) obtained in said one microphone; (f) extracting a variation in the cross-correlation between said input signals of said N channels on the basis of said residual echo e(k) and said combined input signal vector x(k); (g) generating an adjustment vector v(k) on the basis of said cross-correlation variation; (h) adjusting said combined estimated impulse response vector h(k) of said combined estimated echo path by said adjustment vector v(k) to obtain a combined estimated impulse vector h(k+1) for use at the next time k+1; and (i) repeating said steps (a) to (h) upon each increment of time k. - View Dependent Claims (2, 3, 6, 7, 8, 9, 10, 11)
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4. An N-channel echo cancellation method comprising the steps of:
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(a) radiating an input signal xn (k) of each channel n, (n=1, . . . N) as an acoustic signal by a loudspeaker of said each channel, said input signal being inputted as a sample every discrete time k and N being an integer equal to or greater than 2; (b) picking up, by one microphone, said N acoustic signals propagating thereto over N echo paths from said N loudspeaker to obtain an echo y(k); (c) obtaining a combined input signal vector x(k)=[x1T (k), x2T (k), . . . , xNT (k)]T by combining input signal vectors xn (k) of said N channels, each composed of an input signal sequences xn (k), xn (k-1), . . . , xn (k-Ln +1) counted back to time Ln -1 from said discrete time k in each channel; (d) calculating an approximate estimated echo, by a convolution zT (k)x(k), which is obtained by inputting said combined input signal vector x(k) into a combined approximate estimated echo path which has a approximate estimated impulse response vector zn (k), n=1, . . . , N of N estimated echo paths corresponding to said N echo paths, each of said N estimated echo paths having Ln taps; (e) calculating an auto-correlation vector rp-1 (k) of said combined input signal vector x(k); (f) generating a supplementary estimated echo on the basis of said auto-correlation vector rp-1 (k) and a smoothing coefficient vector sp-1 (k-1) at time K-1; (g) calculating the sum of said approximate estimated echo and said supplementary estimated echo and outputting it as a combined estimated echo y(k) for said echo y(k); (h) calculating a residual echo e(k) by subtracting said combined estimated echo y(k) from said echo y(k) obtained in said one microphone; (i) detecting, as pre-filter coefficients β
1, . . . , β
p, variations in the cross-correlation between said input signals by using current and previous ones of said combined input signal vector x(k) through the use of said residual echo e(k) and said combined input signal vector x(k);(j) generating a smoothing coefficient vector sp-1 (k) by smoothing said pre-filter coefficients β
1, . . . , β
p ;(k) adjusting said approximate estimated impulse response vector z(k) on the basis of said smoothing coefficient vector sp-1 (k) and said previous combined input signal vector x(k-p+1) to obtain an approximate estimated impulse response vector z(k+1) for use at the next time k+1; and (l) repeating said steps (a) to (k) upon each increment of time k. - View Dependent Claims (5)
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12. An N-channel echo canceller comprising:
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N loudspeakers for radiating input signals xn (k), n=1, . . . , N, as acoustic signals of respective channels, said input signals being inputted as samples every discrete time k and N being an integer equal to or greater than 2; a microphone for picking up said N acoustic signals propagating thereto over N echo paths from said N loudspeaker to obtain en echo y(k); a vector combining part for obtaining a combined input signal vector x(k)=[x1T (k), x2T (k), . . . , xNT (k)]T by combining input signal vectors xn (k) of said N channels, each composed of an input signal sequence xn (k), xn (k-1), . . . , xn (k-Ln +1) counted Ln -1 back from said discrete time k in each of said N channels; an estimated echo generating part which has a combined estimated impulse response vector h(k) obtained by combining estimated impulse response vectors h(k), n=1, . . . , N of N estimated echo paths corresponding to said N echo paths, each of said N estimated echo paths having Ln taps, and into which said combined input signal vector x(k) is inputted to generate an estimated echo y(k); a subtractor for obtaining a residual echo e(k) by subtracting said estimated echo y(k) from said echo y(k) provided from said microphone; a cross-correlation variation extracting part for extracting a variation in the cross-correlation between said input signals of said N channels on the basis of said residual echo e(k) and said combined input signal vector x(k) and for generating an adjustment vector v(k); and an adjusting part for adjusting said combined estimated impulse response vector h(k) by said adjustment vector v(k) to obtain a combined estimated response vector h(k+1) for use at the next time k+1. - View Dependent Claims (13, 16, 17, 18, 19, 20, 21)
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14. An N-channel echo canceller comprising:
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N loudspeakers for radiating input signals xn (k), n=1, . . . , N, as acoustic signals of respective channels, said input signals being inputted as samples every discrete time k and N being an integer equal to or greater than 2; a microphone for picking up said N acoustic signals propagating thereto over N echo paths from said N loudspeaker to obtain en echo y(k); a vector combining part for obtaining a combined input signal vector x(k)=[x1T (k), x2T (k), . . . , xNT (k)]T by combining input signal vectors xn (k) of said N channels, each composed of an input signal sequence xn (k), xn (k-1), . . . , xn (k-Ln +1) counted Ln -1 back from said discrete time k in each of said N channels; an approximate estimated echo path adjusting part which has set therein a combined approximate impulse response vector z(k) obtained by combining approximate estimated impulse response vectors zn (k), n=1, . . . , N, of N estimated echo paths corresponding to said N echo paths, each of said N estimated echo paths having Ln taps, and into which said combined input signal vector x(k) is inputted to calculate an approximate estimated echo by a convolution zT (k)x(k); a auto-correlation calculating part for calculating an auto-correlation vector rp-1 (k) of said combined input signal vector x(k); an adder for calculating the sum of said approximate estimated echo and a supplementary estimated echo and for outputting it as a combined estimated echo y(k) and said N estimated echo paths corresponding to said N echo paths; a subtractor for obtaining a residual echo e(k) by subtracting said combined estimated echo y(k) from said echo y(k) obtained in said microphone; a cross-correlation variation coefficient calculating part for detecting, as pre-filter coefficients β
1, . . . , β
p, variations in the cross-correlation between current and previous ones of said combined input signal vector x(k) through the use of said residual echo e(k) and said combined input signal vector x(k);a smoothing coefficient vector generating part for generating a smoothing coefficient vector sp-1 (k) by smoothing said pre-filter coefficients; an approximate estimated echo path adjusting part for adjusting said approximate estimated impulse response vector z(k) on the basis of said smoothing coefficient vector sp-1 (k) and a previous one of said previous combined input signal vector x(k-p+1) and for outputting an approximate estimated impulse response vector z(k+1) for use at the next time k+1; and A convoluting part for calculating the inner product of said auto-correlation vector rp-1 (k) and said smoothing coefficient vector sp-1 (k) to obtain said supplementary estimated echo for use at said time k. - View Dependent Claims (15)
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Specification