A gain control system for dynamically tuning an echo canceller, the echo canceller being configured to estimate an echo of a far-end signal and subtract that echo estimate from a microphone signal to output an echo cancelled signal, the system comprising a monitoring unit configured to estimate an energy associated with an impulse response of an adaptive filter configured to generate the echo estimate from the far-end signal, and a gain tuner configured to adjust an attenuation of at least one of the microphone signal and the far-end signal in dependence on the estimated energy. Embodiments of the invention include a threshold control system for controlling a non-linear processor (NLP) in an echo canceller. An aim of both the threshold control system and the gain control system is to obtain some indication of the stability of the adaptive filter. This indication is then used to automatically tune the operational parameters of the echo canceller the non-linear processor threshold in the case of the threshold control system and attenuation in the case of the gain controller and thus avoid the need to manually tune these parameters.
Gain control in an echo canceller