An efficient algebraic codebook structure for CS-ACELP based speech codecs

The algebraic codebook search methods adopted by ITU-T G.729 and its annexes have high computational load and search time. To reduce the code-search time and computational load of Conjugate Structure-Algebraic Code-Excited Linear Prediction (CS-ACELP) coders, we propose a new algebraic codebook structure. In this proposed technique the structure of G.729 algebraic codebook is modified such that it uses only 4 tracks occupying 10 positions each instead of using 5 tracks occupying 8 positions each. The existing search methods are applied on the new codebook structure to have a good comparative study. The experimental and simulation results show that the proposed structure reduces the computational load and code-search time with good Perceptual Evaluation of Speech Quality (PESQ) value. Search load is reduced to approx 75% for Exhaustive search and Focused search algorithms and approx 81% for Depth first tree search algorithm for the proposed structure.