Echo canceller with adaptive residual center clipper controlled by echo estimate

摘要

Residual noise control is provided on telecommunications links which are at least partly 4-wire, by means of a variable threshold center clipper 30 applied to the output of an echo canceller 100. The threshold of the center clipper 30 is varied in accordance with the magnitude of an echo estimate 21 generated by the echo canceller 100.PPIn order to prevent mutilation of near end speech the clipper is disabled when such speech is detected. However, the echo canceller 100 remains in circuit to allow control of echo even during doubletalk.PP The clippers threshold may be controlled in response to the instantaneous modulus of the echo estimate. Alternatively, the echo estimate may be fed to a modular 60 and filter 55 to provide a short term filtered version of the echo estimate which allows control of other components of residual noise.