Classified vector excitation speech coding

Code excited linear prediction (CELP) has been shown by M.R. Schroeder and B.S. Atal (1985) to be capable of achieving high quality speech compression at very low bit rates. However, the original method suffers from the two drawbacks that it requires a large amount of computation, and the Gaussian codebook used is not able to reproduce a sharp impulse in the coded residual waveform. The authors present a classified vector excitation coding (CVXC) scheme based on selective modelling of the LPC residual which attempts to overcome both these drawbacks by using separate codebooks for separate excitation types. A further feature of the authors coder which helps preserve the nature of pulsive residuals, is the use of pairwise nearest neighbour (PNN) matching to generate the excitation codebooks.