Constrained Voicing-Based Codebook in Low-Rate Wideband CELP Coding

In this work we propose an efficient technique to quantize the immitance spectral frequency (ISF) in an algebraic code-excited linear prediction (ACELP) wideband codec. The Constrained Voicing-Based Vector Quantization (C-VBVQ) presented in this paper improves substantially the performance of the unconstrained-VBVQ approach for both clean and noisy speech. Both techniques reduce the codebook search time by almost one third. However, in the C-VBVQ training phase, the three codebooks that are individually designed for voiced, unvoiced and transition speech, are jointly reoptimized to impose a structural configuration. The proposed technique reduces the processing delay since it restricts the quantization of an input vector to only one smaller but optimal codebook. For each speech frame, one codebook is selected from the set of three codebooks based on the interframe correlation of the spectral information. The C-VBVQ was successfully implemented in an ACELP wideband coder. The objective and subjective performance are not only superior to that of the combination of the split vector quantization and multistage vector quantization but also to the unconstrained VBVQ.