Flexible frequency decompositions for cosine-modulated filter banks

We investigate the use of nonuniform cosine-modulated filter banks for audio coding. A rate-distortion framework is employed, similar to the work in Herley et al. (1994), to select the filter bank structure from a large library of possible frequency decompositions. A new flexible frequency decomposition algorithm is proposed that jointly optimizes the filter bank structure and the bit allocation over the subband channels. Experimental results for both synthetic and real audio signals are provided. The new algorithm shows significant improvements in comparison with fixed uniform frequency decompositions, but special care has to be taken to reduce the size of the decomposition overhead.