Speech transcoding from AMR to G.729 in excitation domain

When speech communication happens between two networks which adopt different speech coding standards, transcoding is always needed. In the transcoding between coding standards based on code-excited linear prediction, the fixed codebook usually needs to search due to the different structures between them. A transcoding method in excitation domain from AMR in modes with different fixed codebook structures to G.729 is presented, including transcoding with and without periodicity enhancement. In this transcoding, besides the translation of LSPs, pitch delays, and gains of adaptive codebooks and fixed codebooks as usual, fixed codebooks of different coding standards with diverse codebook structures can be translated efficiently according to MMSE rule. Experiment results indicate that, the transcoding without periodicity enhancement has less computational complexity than that with periodicity enhancement, even much less than tandem transcoding, yet maintains similar speech quality. In most cases, their PESQ scores are very similar.