An efficient method for multi-tap Long Term Predictor (ltp) transcoding: Application to ITU-T G723.1

Network interconnections cause interoperability problems between different speech coding formats. Today, tandem (decoding/re-encoding) is currently used in communication chains. To overcome tandem drawbacks (complexity, quality degradation, delay), intelligent solutions have been proposed to efficiently transcode CELP coders parameters. This paper focuses on CELP Long Term Predictor (LTP) parameters transcoding. First, a survey of LTP transcoding methods is given. Then a novel method is described for multitap LTP transcoding. The multitap gain vector codebook search is restricted to ordered subsets selected from LTP gain parameter of the first coder. This technique is applied to intelligent transcoding towards ITU-T G. 723.1. It achieves same quality as tandem while strongly reducing complexity.