Research And Implementation Of A Speech Codec Algorithm

Speech coding is one of the techniques most closely associated with everyday life. With a wide range of application, it has made a lot of very sophisticated results. Among them, ITU-T G.723.1 is a superior performance of the voice-encoding scheme, a typical modern speech coding core technology. In this paper, for the ITU-T G.723.1 codec algorithm, we conduct in-depth research and improvement; further, based on the TMS320VC5420 DSP chip platform, we achieve the experimental verification of the improved G.723.1 codec algorithm by assembly language. The main work is as follows:(1) Algorithm theory research and implementation: In-depth study of the G.723.1 algorithm, a detailed analysis of the main principles of the codec algorithm module, and simulation implementation by high-level assembly language.(2) Reduce the bit rate: In some applications, we need a voice compression algorithm with a lower encoding rate and compatibal algorithm framework with G.723.1. The paper improves G.723.1 algorithm and compress the bit rate from 5.3 kbps to 4.75 kbps, while keeping the algorithm structure and main modules unchanged. PESQ voice quality objective evaluation showed that voice quality of the improved algorithm, although slightly lower than G.723.1, is better than the same rate algorithm of ETSI AMR 4.75 kbps, and far better than the same rate algorithm of FS1016 (the U.S. Department of Defense).(3) Study on the sensitivity of code word bits. The paper also studies how to improve the ability of anti-channel error of G.723.1 (and its improved algorithm). The core is to study the impact on the decoding voice quality when the coding bits error occurs. Based on the Monte Carlo simulations, the paper uses random error simulation and PESQ voice qulity objective evaluation to build a reasonable and complete testing system. Simulation test results and the general conclusions of comventional speech coder are similar, but more precise and accurate.(4) DSP implementation: based on the TMS320VC5420 DSP chip platform, the paper achieves the G.723.1 codec algorithm by assembly language. Tests show that the complexity of codec algorithm is less than 30 MIPS, reaching the needs of pratical application.