Residual signal in sub-band acoustic echo cancellers

All-pass based Power Symmetric QMF-IIR (PS-QMF-IIR) and Aliasing Cancellation QMF-FIR (AC-QMF-FIR) sub-band decomposition approaches are studied in the context of Acoustic Echo Cancellation. The properties of the residual echo signal are obtained. For both filter types, if the filters have very sharp transition-bands, the residual echo signal contains tonal components. It is shown that these can be efficiently removed by using notch filters. Experimental results indicate that PS-QMF-IIR filters are better suited for this application than FIR filter based sub-band approaches, when combined with the notch filters presented.