Subband echo canceller with adjustable coefficients using a series of step sizes
First Claim
1. An echo canceller comprising:
- first subband analysis means wherein a received input signal to be provided on an echo path is analyzed into N subbands, N being an integer equal to or greater than 2;
N estimated echo path means formed by digital filters through which said N subband-analyzed received input signals are passed to obtain N subband echo replica signals;
second subband analysis means wherein an echo signal resulting from the transmission of said received input signal via said echo path is analyzed into said N subbands;
N subtracting means which subtract, from said N subband-analyzed echo signals, corresponding ones of said N subband echo replica signals to obtain N subband residual echo signals;
subband synthesis means for synthesizing said N subband residual echo signals into a full band residual echo signal; and
N coefficient calculation means each supplied with one of said N subband received input signals and that one of said N subband residual echo signals corresponding thereto, for calculating coefficients of one of said N digital filters, said coefficients of said N digital filters being provided to said N estimated echo paths;
said coefficient calculation means in each subband being operative to iteratively calculate values for adjusting said coefficients of said digital filter of each subband by a series of step sizes predetermined in accordance with exponential attenuation characteristics of an impulse response of said echo path in each subband, and being operative to adjust said coefficients on the basis of said adjusting values and to provide said adjusted coefficients to said digital filter, whereby an impulse response of said estimated echo path in each subband, formed by said digital filter, is caused to approach said impulse response to said echo path in said subband to thereby minimize said residual echo signal in said subband.
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Abstract
A received input signal and an echo signal resulting from the passage of the received input signal through an echo path are both analyzed or divided into a plurality of common subbands. The received input signal in each subband is supplied to an estimated echo path provided in the subband, by which it is rendered into an echo replica signal. The echo replica signal is subtracted, by a subtractor provided in each subband, from the echo signal in the same subband as the echo replica signal to obtain a residual echo signal. The residual echo signals in the respective subbands are synthesized into a full-band residual echo signal. The estimated echo path in each subband is formed by a digital FIR filter and its filter coefficients are calculated by a coefficient calculation part in the subband, based on the received input signal, the residual echo signal and a step size matrix. The filter coefficients are iteratively updated so that the residual echo signal in each subband may be minimized. The step size matrix is used to define the step size of the filter coefficients and is determined by an acoustic field characteristics calculation part, based on the variation characteristics of an impulse response of the echo path in each subband.
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Citations
13 Claims
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1. An echo canceller comprising:
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first subband analysis means wherein a received input signal to be provided on an echo path is analyzed into N subbands, N being an integer equal to or greater than 2; N estimated echo path means formed by digital filters through which said N subband-analyzed received input signals are passed to obtain N subband echo replica signals; second subband analysis means wherein an echo signal resulting from the transmission of said received input signal via said echo path is analyzed into said N subbands; N subtracting means which subtract, from said N subband-analyzed echo signals, corresponding ones of said N subband echo replica signals to obtain N subband residual echo signals; subband synthesis means for synthesizing said N subband residual echo signals into a full band residual echo signal; and N coefficient calculation means each supplied with one of said N subband received input signals and that one of said N subband residual echo signals corresponding thereto, for calculating coefficients of one of said N digital filters, said coefficients of said N digital filters being provided to said N estimated echo paths; said coefficient calculation means in each subband being operative to iteratively calculate values for adjusting said coefficients of said digital filter of each subband by a series of step sizes predetermined in accordance with exponential attenuation characteristics of an impulse response of said echo path in each subband, and being operative to adjust said coefficients on the basis of said adjusting values and to provide said adjusted coefficients to said digital filter, whereby an impulse response of said estimated echo path in each subband, formed by said digital filter, is caused to approach said impulse response to said echo path in said subband to thereby minimize said residual echo signal in said subband. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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Specification