A fast ACELP codebook search method

The ACELP coding algorithm has been widely adopted in standard speech coders due to the advantages of codebook storage and the efficient search scheme. Especially, the focused search and the depth first tree search are very efficient methods dramatically reducing the search complexity while providing a good sub optimal solution. In this paper, we propose a fast algebraic codebook search method which improves the depth first tree search method: The proposed method reduces the search complexity by pruning the trees which are less possible to be selected as an optimum excitation. This method needs no additional computation for the selection of trees to be pruned and reduces the computational complexity considerably compared with the original depth first tree search method with very slight degradation of speech quality. We also implemented a GSM EFR codec chosen as an example to examine our method on the 16 bit fixed-point DSP.