High-performance IIR QMF banks for speech subband coding

In this paper, two high-performance implementations of IIR QMF banks for speech coding are proposed. The first implementation involves a perfect reconstruction (PR) QMF bank while the second is a tree-structured filter bank. In contrast to existing implementations of PR QMF banks, our approach does not require the transmission of initial conditions nor the design of synthesis filters which are more complex than their analysis counterparts. In systems with delay constraints, the tree structured IIR QMF bank can be used; a 4-channel scheme shows a low delay of about 1.9 ms (15 samples) at an 8 kHz sampling rate. No existing FIR QMF banks can achieve this low delay. Moreover, the phase distortion of the low-delay filter bank does not appear to affect the perceptual quality of the processed speech signals. Subjective tests were conducted to evaluate the speech quality