Echo canceller processing techniques and processing

摘要

Residual echo from an echo canceler circuit is reduced by a variable attenuator that operates in response to a processing circuit which determines and adjusts an attenuation factor. The attenuation factor is determined by comparing relative levels of the send input signal, the receive input signal, and the error signal remaining after removal of an expected echo signal from the send input signal. The variable attenuator provides linear power attenuation of the error signal in order to reduce transmission of the residual echo signal and to eliminate the perception of coupling and decoupling of the telephone connection which occurs in known echo cancelers employing center clipping. A noise injection circuit provides a noise signal that is injected into the transmitted signal in inverse proportion to the attenuation of the error signal in order to provide a constant noise level in the transmitted signal as the error signal is variably attentuated.