Variable dimension spectral coding of speech at 2400 bps and below with phonetic classification

The low bit rate enhanced multiband excitation or EMBE speech coder adds several important new features including phonetic classification and a naval spectral quantization technique called variable dimension vector quantization (VDVQ) to the basic multiband excitation vocoder. Phonetic classification allows the adaptation of spectral modeling and quantization to the local acoustic-phonetic character of the speech signal, enhancing quality and robustness. The VDVQ scheme quantizes the log-spectrum with relatively few bits while preserving perceptually important features. Both the fixed rate (2.4 kb/s) and the variable rate (1.44 kb/s average) implementations of EMBE deliver speech quality comparable to the 4.8 kb/s Federal Standard 1016 CELP coder and the 4.15 kb/s Inmarsat-M standard IMBE coder