The Algorithm and Real-time Implementation of 2.4kbps LPC Vocoder with Mixed Excitation
Zhang Xiongwei Zhang Kui Chen Xianzhi
2.4kbps LPC vocoder can be widely used in narrowband digital communication, satellite VSAT channel and ISDN, etc. The conventional LPC vocoder can synthesize speech with fairly high intelligibility and naturalness, but its quality doesn't satisfy the general subscribers. The main reason for its poor quality lies in the use of an over-implified excitation model. In this paper, we propose a new LPC vocoder algorithm which uses the mixed excitation model. It is called M—LPC algorithm. Compared with the conventional LPC algorithm, the M—LPC algorithm improves a lot in the aspects of excitation source, pitch detection and synthesis, etc. The computer simulation results show that the M—LPC algorithm can produce high quality speech at 2.4kbps. The M—LPC algorithm has been implemented using MS320C25, and informal listening tests indicate that the quality of 2.4kbps vocoder employing M—LPC algorithm is very satisfactory.