M-LCELP Speech Coding at 4kb/s with Multi-Mode and Multi-Codebook

Kazunori OZAWA  Masahiro SERIZAWA  Toshiki MIYANO  Toshiyuki NOMURA  Masao IKEKAWA  Shin-ichi TAUMI  

IEICE TRANSACTIONS on Communications   Vol.E77-B   No.9   pp.1114-1121
Publication Date: 1994/09/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Mobile Multimedia Communications)
speech coding,  vector quantization,  speech processing,  dsp,  cellular telephone,  

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This paper presents the M-LCELP (Multi-mode Learned Code Excited LPC) speech coder, which has been developed for the next generation half-rate digital cellular telephone systems. M-LCELP develops the following techniques to achieve high-quality synthetic speech at 4kb/s with practically reasonable computation and memory requirements: (1) Multi-mode and multi-codebook coding to improve coding efficiency, (2) Pitch lag differential coding with pitch tracking to reduce lag transmission rate, (3) A two-stage joint design regular-pulse codebook with common phase structure in voiced frames, to drastically reduce computation and memory requirements, (4) An efficient vector quantization for LSP parameters, (5) An adaptive MA type comb filter to suppress excitation signal inter-harmonic noise. The MOS subjective test results demonstrate that 4.075kb/s M-LCELP synthetic speech quality is mostly equivalent to that for a North American full-rate standard VSELP coder. M-LCELP codec requires 18 MOPS computation amount. The codec has been implemented using 2 floating-point dsp chips.