Adaptive long-term coding of LSF parameters trajectories for large delay / very- to ultra-low bit-rate speech coding

Laurent Girin (1)

1 GIPSA-MAGIC - GIPSA - Machines parlantes, Gestes oro-faciaux, Interaction Face-à-face, Communication augmentée

This paper presents a model-based method for coding the LSF parameters of LPC speech coders on a "long-term" basis, i.e. beyond the usual #20ms frame duration. The objective is to provide efficient LSF quantization for a speech coder with large delay but very- to ultra-low bit-rate (i.e. below 1kb/s). To do this, speech is first segmented into voiced/unvoiced segments. A Discrete Cosine model of the time-trajectory of the LSF vectors is then applied to each segment to capture the LSF inter-frame correlation over the whole segment. Bi-directional transformation from the model coefficients to a reduced set of LSF vectors enables both efficient "sparse" coding (using here multi-stage vector quantizers) and the generation of interpolated LSF vectors at the decoder. The proposed method provides up to 50%-gain in bit-rate over frame-by-frame quantization while preserving signal quality, and competes favorably with 2D-transform coding for the lower range of tested bit-rates. Moreover, the implicit time-interpolation nature of the long-term coding process provides this technique a high potential for use in speech synthesis systems.

Mots clés: Very-/ultra-low bit-rate speech coding; LPC coder; LSF quantization; long-term model; LSF trajectories

Domaines: Traitement du signal et de l'image [eess.SP]; Traitement du signal et de l'image [eess.SP]

Laurent Girin. Adaptive long-term coding of LSF parameters trajectories for large delay / very- to ultra-low bit-rate speech coding. EURASIP Journal on Audio, Speech, and Music Processing, 2010, 2010 (Article ID 597039), pp.n/c. ⟨10.1155/2010/597039⟩. ⟨hal-00534492⟩