Subband echo cancellation in automatic speech dialog systems

Echo cancellation has been most widely studied for hands-free telephony and for cancelling line echos in telephone central o ces. The problem of echo cancelling in speech dialog systems is similar, however it has some speci c requirements. In this contribution, a subband echo cancellation structure is proposed which can be integrated in the feature extraction part of a recognizer. A NLMS gradient-based adaptation is performed in frequency subbands that can either be derived directly from FFT analysis of input speech signal, or by using a proposed reduced-subband approach where the number of subbands is reduced in order to lessen the aliasing e ect of the FFT. A double-talk detector is proposed based on the estimated error function for decision on stopping the adaptation. Finally, a new approach of combining echo cancellation and noise reduction is proposed.