An iterative training method is proposed for the design of random codebooks and channel code mapping tables for a CELP coder. The method is based on a structured excitation source such as a conjugate structure, pitch isynchronization, rotation of samples, time-domain sloped gain, and code mapping to channel code. Closed-loop distortion measure, that is, perceptually weighted distortion between the input and the synthesized speech, is used in all training procedures. The training improves the SNR by around 1 dB and improves subjective quality. The channel code mapping and channel-matched distortion measure increases robustness against channel error.

Keywords: codebook, CELP, training, code mapping