An 8 kb/s low complexity ACELP speech codec
Cheng Deyuan · 2002
An 8 kb/s ACELP speech codec is proposed. The encoding algorithm is based on code-excited linear prediction (CELP) with a multi-level pulse amplitude algebraic codebook (ACELP). Only integer pitch delay is searched. There are 8 non-zero pulses with fixed amplitudes, each of +1, or +0.5, or -1 or -0.5, or zero in each algebraic codevector of length of 64 samples. An efficient nonexhaustive codebook search method is developed. The codevector's gain and LSP frequencies are scalar quantized. An adaptive pitch prefilter before LP synthesis filter and a spectral postfilter after LP synthesis filter are adopted in the speech decoder to enhance the reconstructed speech quality.