September 22-25, 1997
This paper deals with the coding of spectral envelope parameters for very low bit rate speech coding (inferior to 500 bps). In order to obtain a sufficient intelligibility, segmental techniques are necessary. Variable dimension vector quantization is one of these. We propose a new interpretation of already published research from Chou- Lockabaugh  and Cernocky- Baudoin-Chollet [4,6] on the quantization of variable length sequences of spectral vectors, named respectively Variable to Variable length Vector Quantization (VVVQ) and Multigrams Quantization (MGQ). This interpretation gives a meaning to the Lagrange multiplier used in the optimization criterion of the VVVQ, and should allow new developments as, for example, new modelization of the probability density of the source. We have also studied the influence of the limitation of the delay introduced by the method. It was found that a maximal delay of 400 ms is generally sufficient. Finally, we propose the introduction of long sequences in the segmental codebook by linear interpolation of shorter ones.
Bibliographic reference. Baudoin, Geneviève / Cernocky, Jan / Chollet, Gérard (1997): "Quantization of spectral sequences using variable length spectral segments for speech coding at very low bit rate", In EUROSPEECH-1997, 1295-1298.