Some experiments of 7 kHz audio coding at 16 kbit/s

The problem of coding speech at 7 kHz is considered. A possible application of these codecs could be the videophone, especially for hands-free telephone use. The authors propose a split-band coder structure, where both hands are coded with analysis-by-synthesis techniques in order to take advantage of their high coding gain. Two techniques are considered: multipulse coding and codebook-excited linear prediction. The structures of two possible codecs are described, and indications are given of the considerations that led to their design. Their main characteristic is the use, as far as possible, of excitation model parameters optimized within the analysis by synthesis loop, still maintaining a reasonable computational complexity. Subjective and objective results, obtained with high-quality speech, are reported. They show that the obtained speech quality is close to the original