A high quality 4 kb/s multiple pulse-dispersion ACELP speech coder

Pulse dispersion is a very efficient technology to improve the speech quality of a low bit-rate code-excited linear-prediction (CELP) coder. A novel high quality 4 kb/s algebraic CELP (ACELP) speech coder is presented. Different pulse-dispersion technologies are applied to both encoder and decoder to reduce the adverse effects of the sparse algebraic codebook vector and improve the perceptual quality of noise-like and unvoiced speech. Also, pitch preemphasis technology is introduced to improve the robustness of pitch analysis. An harmonic-enhancement technology is introduced to enhance the performance of the fixed codebook further. Informal tests show that the speech quality of the presented 4 kb/s speech coder is very close to that of the 4.75 kb/s coder of ETSI AMR.