Quantization Noise Shaping in Oversampled Filter Banks

The use of a noise-shaping system in oversampled filter banks has been shown to improve the effective resolution of subband coders. Although the filter banks directly determine the noise-shaping coefficients, a comparison between theoretical and simulated results has not been done, while the effect of the selection of the filter banks on the performance of the noise-shaping system has not yet been evaluated. Therefore, an algorithm for the generation of cosine-modulated perfect-reconstruction filter banks is presented, such that the generated filters could be used as a test bed. The optimal noise-shaping coefficients are then derived, and the noise-shaping system is inserted into the subband coder. It is found that the theoretical results agree with the simulations, but that the performance of the noise-shaping system is limited by ill-conditioning at higher system orders. An increase in filter length and an increase in the degree of overlap between neighbouring channels contribute independently to a better performance. Also, it is seen that nearperfect reconstruction filter banks are limited by their reconstruction error but yield good results at low bitrates.