%0 Journal Article
%T Adaptive Long-Term Coding of LSF Parameters Trajectories for Large-Delay/Very- to Ultra-Low Bit-Rate Speech Coding
%A Laurent Girin
%J EURASIP Journal on Audio, Speech, and Music Processing
%D 2010
%I Springer
%R 10.1155/2010/597039
%X This paper presents a model-based method for coding the LSF parameters of LPC speech coders on a ˇ°long-termˇ± basis, that is, beyond the usual 20¨C30 ms 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 1 kb/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 interframe correlation over the whole segment. Bi-directional transformation from the model coefficients to a reduced set of LSF vectors enables both efficient ˇ°sparseˇ± coding (using here multistage 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.
%U http://dx.doi.org/10.1155/2010/597039