Fast mpeg audio subband decoding using a multimedia processor

Abstract

A decoding process for a MPEG1 audio subband uses the symmetry of filter coefficients to reduce the number of multiplications required to decode an audio subband. The decoding process can be efficiently implemented on a single-instruction-multiple-data (SIMD) processor having vector registers capable of holding multiple samples from the subband. In a particular embodiment, some of samples are stored in a first vector register in a normal order and other samples are stored in a second vector register in a reverse order. For example, for eight data element vector registers, the first vector register contains a series of samples index values 0 to 7, and the second vector register contains a series of samples index values 31 to 24. Such ordering facilitates SIMD instructions which perform parallel operations combining value of index i with values of index 31-i. In accordance with another aspect of the invention, time domain samples having odd and even time indices are determined in parallel using vectors having data elements with indices corresponding to the time indices and a sign vector where each data element of the sign vector is positive or negative according to whether the associated time index is even or odd.