Applications of wavelets to Speech processing: A case study of a celp coder

Wavelets are a new family of orthogonal basis functions for representing finite energy signals. In this chapter, we provide a brief review of wavelets and their properties. We cite a number of applications of wavelets to speech processing that have been proposed recently. As a detailed case study in wavelet applications, we present our work on a wavelet-transform-based CELP coder design for high-quality speech coding at about 4.8 kbits/s. The coder quantizes the second residual using a wavelet transform approach instead of the stochastic-codebook-based vector quantization normally used in CELP coders, including the U.S. Federal Standard FS 1016 coder at 4.8 kbits/s. The wavelet coder improves the computational efficiency for encoding the second residual by requiring only 1.2 MIPS instead of 8.3 MIPS required by FS 1016. Subjective speech quality tests involving pairwise comparisons show that the wavelet coder was preferred 61% of the time over FS 1016.