Improvement issues on transcoding algorithms: for the flexible usage to the various pairs of speech codec

The paper describes important issues on transcoding between different speech codecs by considering the paradigms of source and target coders. Conventional transcoding algorithms on LSP, pitch and adaptive/fixed codebook conversion are refined with regard to the structure of the coders. In addition, a new perceptual weighting filter, that plays a role in the post-filter and perceptual weighting filter together, is proposed to improve the performance further. The performance of the proposed algorithms is verified in a step-by-step manner with examples of transcoding between AMR, G.723.1 and G.729. By applying the proposed algorithm to the transcoders, the complexity is reduced by about 20-76.88% and quality is also improved compared to conventional approaches.