T. Moriya et al., TRAINING METHOD OF THE EXCITATION CODEBOOKS FOR CODE-EXCITED LINEAR PREDICTION, Electronics and communications in Japan. Part 3, Fundamental electronic science, 77(11), 1994, pp. 34-44
This paper considers the codebook for low bit-rate speech coding by co
de-excited linear prediction (CELP) and the mapping table for the chan
nel code. It also proposes an optimization procedure for sequential tr
aining based on the structured excitation codebook. In the discussions
of structurization of the codebook, the conjugate structure to repres
ent the output by the sum of two vectors, the pitch synchronized proce
ssing, rotating use of the codebook, the time-domain sloped gain, and
the integrated mapping to the channel code are considered. The distort
ion measure used in the training is the same closed-loop measure as is
used in the coding. In other words, the distortion between the input
speech and the synthesized speech at the perceptually weighted filter
output is minimized. By training the codebook, the SNR of the coded sp
eech is improved by approximately 1 dB. The improvement in speech qual
ity is also verified. It is also verified that the robustness against
bit error can be improved by the training of the mapping table to the
channel code, as well as by training based on the distortion measure c
onsidering bit error.