Embedded Wideband Vselp Speech Coding With Optimized Codebooks

The need of variable bit rate actually exists for an increasing number of applications such as videoconferencing, audioconferencing and packet circuit multiplication. In this contribution we extend the concept of variable bit rate to multi-stage VSELP coding. First we begin with an unified approach for multi stage CELP and VSELP coding and we show that codebooks orthogonalization leads to optimum embedded coders for variable bit rates. Then we derive a new algorithm for the off-line optimization of the basis vectors in the multi-stage case. Finally we give some subjective test results obtained with 24 and 32 kbitts embedded wideband speech coders.