Acoustic echo control in subbands — An application of multirate systems

This paper discusses the application of multirate signal processing techniques for the design of a system to cancel acoustic echoes in subbands. After a description of the computational complexity and the filterbank design, the need of delaying the microphone signal is explained. Aliasing caused by nonideal filterbanks and especially the noncausal subband impulse responses limit the quality of the system. If certain restrictions (e.g. an upper threshold of delay or a finit amount of memory) have to be fulfilled, it is neccesary to "balance" the entire system. Hence, all components should be in the same "quality-range". Finally we point out the advantages gained by applying multirate processing.