Implementation And Optimization Of 16 Bit Fixed-Point Speech Codec On 24Bit DSP

Accompanied with the development of IP technology, VoIP(Voice over IP, voice communication based on the IP) has been applied widely in recent years. The delay of speech codec plays an important part in the quality of voice, therefore, how to realize a high speed speech codec is becoming the key of the IP technology.At present, most of the fixed-point DSP is 16bit data bus width, which will possibly cause the limitation of data precision, thus increase the complexity of algorithm. The chip AR1688 in the project is 24bit data bus width, and it can reduce the computation, improve the precision. Therefore, it is meaningful to realize the speech codec in the chip.The main task of the paper is the implementation of speech codec in 24bit DSP chip. The main algorithm is G.729 and Speex. Now G.729 is a mature international standard, which was proposed by ITU-T, in 1996. Because of its good effect and high stability, G729 is now widely used in PSTN and gateway. Due to G.729 coming forth early, it is applied widely in a large number of gateways and IP terminals. In order to be compatible with these old equipments, it is necessary to implement the speech codec in new gateways. Therefore, it is a practical significance to implement G.729 algorithm. And it is a practical and research significance to implement Speex algorithm, because of its wide range of bit-rates, integration of narrowband and wideband using an embedded bit-stream, and free open-source, patent and royalty-free. After pass the testing sequence, the next work is the optimization of the speech codec using the hardware features and instruction characteristic of AR1688 chip to reduce the complexity of algorithm, improve the speed of codec, adapt the requirements of processor, and reduce the power of equipment. Eventually, we successfully achieved the requirements of real-time speech codec in AR1688 chip.