Spectral Quantization and Interpolation in CELP Coders

SUMMARY: Recently codebook-excited linear prediction (CELP) coders, also known as stochastic coders, have been investigated for speech coding at low-to-medium bit rates. In the CELP coder one portion of the bits is allocated to quantizing the LPC spectrum, while the remainder is used to characterize the excitation for the LPC filter. Some of the most common LPC parameters used for spectral quantization are the arcsine of the reflection coefficients (RC), the log-area ratios (LAR), and the line spectral frequencies (LSF). Most of these quantization procedures were investigated in the context of vocoder applications and it is not clear whether the results from the vocoder studies are applicable to CELP coders.