Method and apparatus for reducing correlated errors in subband coding systems with quantizers

Abstract

A method and apparatus for reducing correlated errors in subband coding systems with quantizers is disclosed. A subband coding system comprises a plurality of subband analysis filters to divide the frequency spectrum of the input signal into subbands, individual subband quantizers for coding each subband by a preselected number of quantization levels, corresponding subband decoders and subband synthesis filters. The transfer function of each of the subband synthesis filters is advantageously determined based on the transfer functions of the subband analysis filters as well as on the characteristics of the quantizer used to code the corresponding subband. Specifically, the synthesis filter transfer functions may be based on a perfect reconstruction filter bank or a quadrature mirror filter bank, as well as on the gain factors of a gain plus additive noise linear model for the Lloyd-Max quantizers used to code the corresponding subbands. That portion of the error between the input signal and the replica signal as reconstructed by the system which is correlated to the input signal may be advantageously reduced or eliminated, irrespective of that portion of the error which is uncorrelated to the input signal. Thus, the total error in a final signal may be advantageously reduced by the subsequent application of prior art techniques for the reduction of random, uncorrelated noise.

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