An efficient transcoding algorithm for G.723.1 and G.729A speech coders: Interoperability between mobile and IP network

In this paper, an efficient transcoding algorithm for G.723.1 and G.729A speech coders is proposed. Transcoding in this paper is completed through four processing steps: LSP conversion, pitch interval conversion, fast adaptive-codebook search, and fast fixed-codebook search. For maintaining minimum distortion, sensitive parameters to quality such as adaptive- and fixed-codebooks are re-estimated from synthesized target signals. To reduce overall complexity, other parameters are directly converted in parametric levels without running through the decoding process. Objective and subjective preference tests verify that the proposed transcoding algorithm has comparable quality to the classical encoder-decoder tandem approach. To compare the complexity of the algorithms, we implement them on the TI TMS320C6201 DSP chip. As a result, the proposed algorithm achieves 26-38% reduction of the overall complexity with a shorter processing delay.