Research And Realization Of AMR Audio Codec

Speech coding is an important technique in digital audio communication. In the previous coding algorithm, higher coding rate can easily ensure higher quality of speech but occupies larger system resource; however, lower coding rate with reduced cost can hardly ensure the quality of speech. Variable rate speech coding has the ability of changing bit rate dynamically according to the channel conditions. It could trade speech quality and capacity smoothly and flexibly by offering different codec modes to respond to the changing radio and traffic conditions. Also, it could satisfy different requirements of the network and system. Thus it becomes a research hotspot in recent years.Adaptive Multi-Rate(AMR) codec was standardized by 3GPP, in which ACELP(Algebraic Codec-Excited Linear Prediction) algorithm, Voice Activity Detector(VAD) technique, Rate Decision Algorithm(RDA), Error Concealment Units(ECU) and Comfort Noise Aspects(CNA) technique were utilized. It has the ability of switching bit rate from 4.75kb/s to 12.2kb/s according to the channel conditions, so it could trade speech quality and capacity smoothly and flexibly. Recently, with the development of operation speed and operation ability of DSP, it becomes a trend utilizing DSP to implement audio and video arithmetic. TI TMS320C6000 DSPs is now the preferred digitl signal processor of Base Station in communication field.The basic concept of speech processing was introduced in this paper, including the kinds and development trade of speech coding. Then the arithmetic and key technique refered were researched and explored. Part of the formula illation was included, and also the technique of VAD, RDA, ECU and CNA in variable rate speech coding was particularly described. On this base, DSP technique was researched. By software programming and hardware debugging, AMR codec algorithm was implemented on DSP. Furthermore, the code was optimized in many levels so that code and data memory were greatly reduced and the efficiency of the programme was improved. Lastly, radio transceiver was used outside DSP. By the means of interface designe and hardware debugging, a wireless transmission platform was developed on which AMR codec algorithm was validated.