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In this paper, the authors propose 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, they 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, they 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.
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