Multi-band residual coding of CELP codecs at 8 kb/s

We explore the benefits for CELP coding of speech at 8 kb/s of dividing the residual signal after pitch filtering into three band-passed components and using separate codebooks to represent each component. Minimization of the perceptually weighted error between the input signal and the reconstructed signal is divided into several band-limited minimization operations where the lowest frequency match dominates the quality of the result. For equal total numbers of bits allocated to code the residual in a 5 ms frame, spectral division of the coding operation results on the average in a better match than temporal division into subframes. These results permit the design of a high quality speech codec at 8 kb/s with modest delay and low complexity.<>