Variable dimensional algebraic CELP coding of prototype waveforms

We propose a variable dimensional algebraic codebook structure in order to quantize the prototype waveforms efficiently. The proposed algorithm adjusts the interval of candidate pulse positions in a codevector according to the pitch period. The analysis-by-synthesis search procedure is computationally efficient due to the characteristics of the algebraic codebook structure. We also develop a method to perceptually improve the basis pulse of codevectors, which enhances the reconstructed speech quality with little increase in computational complexity. The improved prototype waveform interpolation coder adopting the proposed methods achieves a high quality of speech at 4 kbps