Constrained design of allpass transformed DFT filter-banks by quadratic programming

A novel numerical design approach for allpass transformed DFT filter-banks with subsampling is proposed. Such frequency warped filter-banks possess a non-uniform time-frequency resolution which is of interest, e.g., for speech and audio processing. The coefficients of the FIR synthesis filters are determined by a constrained least-squares error (CLSE) design. Thereby, the stopband energy of the synthesis filters is minimized with the constraint for perfect reconstruction (PR). This design by quadratic programming accounts also for polyphase network (PPN) filter-banks where the prototype filter degree exceeds the number of subbands to facilitate an enhanced frequency selectivity. In contrast to known designs for allpass transformed analysis-synthesis filter-banks (AS FBs), perfect signal reconstruction can be achieved effectively with synthesis filters featuring a pronounced bandpass characteristic.