AIM EFFICIENT TRANSCODING ALGORITHM FOR G.723.1 AND G.729A SPEECH CODERS

摘要

To set a valid communication channel between two endpoints employing different speech coders, decoder and encoder of each endpoint need to be placed in tandem. However, tandem coding is often associated with problems such as poor speech quality, high computational load, and additional transmission delay. In this paper, we propose an efficient transcoding algorithm for a legitimate communication between 5.3 kbps G.723.1 and 8 kbps G.729A coders. The proposed transcoding algorithm is composed of four parts: LSP conversion, open-loop pitch conversion, fast adaptive codebook search, and fast fixed codebook search. In each part of the transcoding algorithm, parameters of the target coder are obtained directly from the parameters of the source coder. The efficiency transcoding algorithm is supported via the computational reduction of about 25-35% in the encoding part. Subjective preference tests as well as objective quality evaluation confirmed that the proposed transcoding algorithm can produce equivalent speech quality to the tandem coding with the shorter processing delay and less computational complexity.