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Abstract

In an echo canceller, an estimated echo signal is produced by an adaptive filter from a receive path signal and is subtracted from an incoming transmit path signal to produce an outgoing transmit path signal. Averages of signal levels on the receive path and the incoming and outgoing transmit paths are produced by exponential averaging. Adaptation of the adaptive filter is inhibited after initial convergence. Adaptation is enabled again in response to an echo attenuation parameter being less than a first threshold value and a variation of an echo attenuation parameter being less than a second threshold value, this situation representing a detected echo path change. The detection of an echo path change is inhibited in the presence of a near end signal. The echo attenuation parameters can be either or both of the ERLE (echo return loss enhancement) due to the subtraction of the estimated echo signal or the combined attenuation of the ERLE plus the ERL (echo return loss) of the hybrid circuit, these parameters being determined from averaged signal levels on the signal paths.

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