Two-Channel IIR QMF banks with approximately linear-phase analysis and synthesis filters

A computationally simple method to obtain IIR analysis and synthesis filters that possess negligible phase distortion is presented. It is shown that for a certain class of FIR filter banks, the polyphase components are approximately all-pass. By applying the balanced reduction procedure to the polyphase components of such an FIR prototype filter all-pass IIR polyphase components are obtained. The resulting IIR designs have negligible phase distortion. Design examples indicate that the derived IIR filter banks can be implemented more efficiently than the FIR prototypes. Results show that the IIR filters are better than linear phase perfect reconstruction systems when implemented in a finite wordlength processor