ISCA Archive Eurospeech 1995
ISCA Archive Eurospeech 1995

Fast low-delay CELP coding of speech at 8kbps

Siu-pun Chui, Cheung-fat Chan

This paper presents a 2.5ms low-delay CELP coder at 8kbps with low complexity. Two major contributions were made in order to achieve this goal The first contribution is based on using hybrid input/output block adaptive linear prediction scheme for short-term analysis. In this scheme, LSP coefficients are used as parameters for spectral adaptation and they are partitioned into two segments; LSPs corresponding to low frequency regions are backward adapted from the reproduction speech while LSPs in high frequency regions are adapted from input speech and quantized as side information to decoder. The rationale behind this scheme is to compensate the spectrum distortion introduced by conventional backward adaptation scheme. The second contribution is a fast method for stochastic codebook search. This method relies on using a vector-sum codebook where the crosscorrelation of any pair of basis vectors is odd-symmetric. As a result of this odd-symmetric crosscorrelation (OSC) property the energy term of the cost function for codebook search is a constant with respect to the search and the optimum codeword can be easily determined by using a sign detection procedure with a complexity almost independent of the codebook size.