A METHOD AND DEVICE FOR DESIGNING AND SEARCHING LARGE STOCHASTIC CODEBOOKS IN LOW BIT RATE SPEECH ENCODERS

摘要

A stochastic codebook structure with low storage requirements is designed and efficiently searched in view of encoding a sound signal. This codebook consists of a set of codevectors, built from a small set of random vectors. Each codevector is obtained by the addition of several signed vectors from the small set (for example 64) of random (e.g. Gaussian) vectors. For example, a codebook which consists of the addition of two signed vectors from a collection of 64 Gaussian vectors gives rise to a 13-bit (8192-entry) codebook (6 bits for each of the two vector and 1 bit for the signs). Similarly, adding 3 vectors from a collection of 64 vectors gives rise to a 19-bit codebook. Besides the memory efficient structure of the codebook, a fast search procedure is used whereby only a small subset of the codebook is searched. In this fast search procedure, a small number of vectors from the collection of random vectors are preselected, and the search is confined to the subset of codebook consisting of these preselected vectors.