Two-stage vector quantization-lattice vector quantization (VQ-LVQ) is used to encode the speech line spectrum pair (LSP) parameters. VQ-LVQ has the advantages of lower implementational complexity and less required memory than split vector quantization (SVQ) and multi-stage vector quantization (MSVQ) with unstructured codebooks. Based on the authors' speech data base and the same spectral measure, VQ-LVQ can save about 3 bits/frame compared to SVQ, and has advantages of about 2 to 3 bits/frame compared to unstructured codebook MSVQ, depending on the number of stages and the survivor path search complexity. The paper also provides a discussion on some factors influencing the evaluation of the LSP encoding performance.
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