Improving transcoding capability of speech coders in clean and frame erasured channel environments

With the trend of merging various networks, a need arises to provide transcoding between different speech coding formats. Presently this means cross tandeming the two coders, but it results in both quality loss and extra delay. A possible alternative is using a bit-stream mapping approach that directly converts parameter values. This paper proposes a bit-stream mapping method between ITU-T Recommendation G.729 and TIA IS-641. Informal listening tests and PSQM scores show that the proposed method has better quality than the cross tandeming method in both clean and frame erased channel environments.