Echo canceller
AssigneeAdaptive Digital Technologies
InventorsScott David Kurtz, Brian Michael McCarthy, Sr.
Life of this patent
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Abstract
A method of echo cancellation for a signal transmission system in which the size of the step used to adapt filter coefficients is adjusted in accordance with the echo delay and in which stationary signals are avoided by determining when the mean and variance of coefficients obtained from a second order linear predictive coding analysis of successive far end samples exceed preset thresholds.
Claims11
A method of echo cancellation for a signal transmission system in which filter coefficients are adapted by cross-correlation of a transmission signal and an error signal, the improvement comprising the steps of:
- determining the echo delay;
- adjusting the step size used to update adaptation of said filter coefficients and said cross-correlation in accordance with the echo delay;
- and
- when there is significant delay, using the product of the most recent value of the far end power and a previous value of far end power that corresponds to the echo delay to normalize said step size.
A method of echo cancellation for a signal transmission system in which filter coefficients are adapted by cross-correlation of a transmission signal and an error signal, the improvement comprising the steps of;
- determining the echo delay;
- adjusting the step size used to update adaptation of said filter coefficients and said cross-correlation in accordance with the echo delay;
- and
- identifying echo tails from multiple, time variant echo sources by determining which echo amplitudes correspond to echoes from independent sources by:
- a. cross-correlating the far signal and the normalized near signal to form a cross-correlation array CC[O . . . (T−1)];
- b. searching said cross-correlation array to find a local maximum for every n samples to form a decimated peak echo array having 1/n the number of samples as the cross-correlation array;
- and
- c. flagging all of the elements associated with said maximum local amplitude to exclude them from being selected for filter adaptation.
A method of operating an echo canceller to avoid stationary signals, comprising:
- a. autocorrelating successive far end samples to obtain three autocorrelation coefficients (CORRI for I=0, 2);
- b. performing a second order linear predictive coding analysis on the three autocorrelation coefficients to obtain two reflection coefficients (RC0 and RC1), (where RC0=−CORR1/CORR0 and RC1=(CORR2*CORR0−CORR12)/(CORRR02−CORR12));
- d. determining that a stationary signal is present when the mean and variance of said reflection coefficients reach preset values;
- and
- e. modifying the processing of said samples when said stationary signals are determined to be present.
Dependencies are inferred from the claim text.