Echo cancelling using adaptive bulk delay and filter

摘要

Telephone circuit echo cancelling is disclosed of the type employing a digital transversal filter which adapts to incorporate the impulse response of the echo producing system in such a way as to cancel the echo. Such impulse responses often include large initial periods of substantially zero response due to transmission delays; the echo cancelling of the invention does not attempt to provide filter coefficients and delays for this initial period. Instead, a bulk delay memory holds signal samples for this initial period and then provides them to the transversal filter input. A method is disclosed for automatically selecting the value of the bulk delay based on input and output signals of the system.