CELP: a candidate for GSM half-rate coding

A systematic study of code excited linear predictive (CELP) coders is presented. The design of an optimized version complying with the specifications for a GSM half-rate coder is described. This study is divided into three parts: election of an unquantized configuration, assuming unquantized scale factors and filter coefficients, fine tuning of the parameter quantization, and adaptation to the GSM specifications. A strong emphasis is placed on efficient codebook search procedures, and two approaches are briefly described: the truncated autocorrelation approach and the unity-magnitude approach. The final coder version achieves a very good combination of speech quality and implementation complexity