Echo canceler with subband attenuation and noise injection control

Abstract

An echo canceler for canceling echo components of a send-input signal, includes an analysis filter bank for dividing the send-input signal into a plurality of subband send-input signals. A receive-signal is also divided into a plurality of subband receive signals. Each of the subband receive signals is convolved with an impulse response function pertaining the echo path coupling the receive signal to the send-input signal within each subband. The convolutions yield a plurality of estimated echo signals, which are then each subtracted from the corresponding subband send-input signal, to produce a plurality of error signals. Residual echo components within the error signals are attenuated by a variable attenuator in response to a comparison of relative levels of corresponding subband send-input Signals, subband receive signals and the error signals. A noise component is injected into each attenuated error signal in order to compensate for attenuation of background noise incidental to the variable attenuation of the error signals. The amplitude of the noise components are each determined independently on the basis of an estimated noise content of the subband send-input signals and in accordance with the applied attenuation within each subband. The attenuated and noise-compensated error signals are combined by a synthesis filter to provide a send-output signal.