Low delay CELP coding at 8 kbps using classified voiced and unvoiced excitation codebooks

This paper presents an 8 kbps low delay CELP coding scheme which has a one way delay less than 5 ms. In the proposed scheme, we classify the analyzed speech as either voiced or unvoiced segment. An adaptive pitch excitation codebook is used to generate voiced speech while a Gaussian stochastic codebook is used to generate unvoiced speech. To eliminate the roughness of synthetic speech without affecting the pitch dynamics, we propose a new long-term prediction algorithm to smooth the pitch contour in the voiced speech segment. Closed-loop excitation gain adaptation is employed to make the coding scheme more robust