Complexity scalability design in coding of the adaptive codebook for ITU-T G.729 speech coder

Using the adaptive codebook and stochastic codebook, the code-excited linear prediction (CELP) speech coders can achieve a good speech quality at low bit rate. When the complexity reduction of the stochastic codebook search reaches a bottleneck, the only way to reduce the complexity of the speech codec would be simplifying the computation of the adaptive codebook. This paper introduces and describes the complexity scalability design for the adaptive codebook search of the G.729 speech coder. Two schemes, the search-range reduction and the dimension-reduced method, for complexity reduction will be discussed. Simulation results show that the proposed approaches can effectively reduce the computational complexity of the close-loop pitch search with imperceptible degradation of the speech quality.