Amplitude quantization for CELP excitation signals

The authors present a computationally expensive method for tuning the innovation coding of a CELP (code excited linear prediction) coder to the LTP coding. Evidence is given, both from vector quantization (VQ) theory and from simulations, that coding the innovation gain with only one bit is feasible by introducing an adaptive procedure. A stochastic codebook of innovations is selected for the simulations. Simulations demonstrate that the density function for the amplitude of an innovation vector is distinctly bimodal. In an analogy to coding of Gaussian vectors, it is shown that this property is in agreement with classical VQ theory