A Low-Bit-Rate Extension Algorithm to the 8 kbit/s CS-ACELP Based on Adaptive Fixed Codebook Modeling

摘要

In this paper, we propose an adaptive encod- ing method of fixed codebook in CELP coders and implement an adaptive fixed code-excited linear prediction (AF-CELP) speech coder as a low-bit-rate extension to the 8 kbit/s CS-ACELP. The AF-CELP can be implemented at low bit rates as well as low complexity by exploiting the fact that the fixed codebook contri- bution to the speech signal is periodic, as is the adaptive code- book (or pitch filter) contribution. Listening tests show that the 6.4 kbit/s AF-CELP has a comparable quality to the 8 kbit/s CS-ACELP under real environmental test conditions.