AN EFFICIENT TRANSCODING SCHEME FOR G.729 AND G.723.1 SPEECH CODECS: INTEROPERABILITY OVER THE INTERNET

摘要

This paper proposes an efficient conversion algorithm for G. 729 and G. 723.1 speech codecs to reduce computational complexity of the communications between the G.729 and G.723.1 speech codecs. The proposed transcoding method incorporates four processes: line spectral pair (LSP) interpolation, pitch conversion, fast adaptive-codebook search, and fast fixed-codebook search. To reduce search computations, we propose a fast adaptive codebook search algorithm that uses residual signals to predict the candidate gain-vectors of the adaptive codebook. For the fixed codebook, we propose a fast search algorithm that uses an energy function to predict the candidate pulse positions. Other codec parameters are directly converted in parametric levels without executing the decoding process. Simulation results show that the proposed methods can reduce total computational complexity by 65.8%, with a shorter coding delay compared with the commonly used decode-then-encode tandem approach. Objective and subjective evaluations were used to verify that the proposed transcoding scheme provides speech quality comparable to the tandem approach.