ISSN : 1796-2021
Volume : 4    Issue : 2    Date : March 2009

Constrained Voicing-Based Codebook in Low-Rate Wideband CELP Coding
Driss Guerchi
Page(s): 71-77
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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.

Index Terms
Wideband speech coding, constrained voicing-based vector quantization, low-complexity ISF