A network speech echo canceller with comfort noise

This paper describes a proposed comfort noise system for a network echo canceller. In this system, any residual echo is suppressed using a single threshold centre-clipper, but instead of transmitting silence to the far-end of the network, a synthetic version of the background sounds is sent. This masks any ‘noise modulation’ or ‘noise pumping’ that may otherwise occur. The background sounds are characterised using linear prediction. Periods when only background sounds are present are identified by a modified GSM Voice Activity Detector (VAD). Informal listening tests have shown that this ‘synthetic background’ is preferable to the transmission of silence or pseudo-random noise that is not spectrally shaped to match the original background.