Research And Realization Of The DTX/CNG Algorithm Based On Scalable Wideband Speech Coder/Decoder System

In normal speech communication, nearly half of the time there is no talking at all. Using this characteristic, Discontinuous transmission/comfortable noise generation (DTX/CNG) technology lower down the coding rate when there is no speech, otherwise elevate the rate. So that the average of the rate will be lower.G.729EV is a new recommendation of scalable wideband coder raised in recent months. In this paper the writer researches on appending DTX/CNG algorithm to G.729EV. CNG is to generate comfortable noise to be similar with the environment noise at the coder side. So when detected there is speech, coding at a normal coding rate, and when no speech, DTX decides when to send SID frame every several frames. The SID parameters are used to generate comfortable noise at the decoder.The chief works that have been done in the paper include:(1) Introduce and discuss the situation and development of DTX/CNG algorithm.(2) Introduce briefly the basic acknowledge of speech coding used in the paper, include: Code Excited Linear Prediction (CELP), Time Domain Bandwidth Extension (TDBWE), vector qualification and so on.(3) Research DTX/CNG algorithm based on G.729EV recommendation.(4) Realize DTX/CNG algorithm at PC based on C language program, and tested based on the standard testing plans provided by ITU.After a series of standard testing, the DTX/CNG algorithm completely matches the requirements of "Terms of Reference (ToR)" provide by ITU. The quality of the synthesized speech nearly no descends after coded and decoded when the average rate is lower down dramatically. And the added complexity and storage of the algorithm are permissive.