A Way To Improve MELP 2.4kbps Speech Codec

Digital speech signal have much more advantages than analog speech signal. It has high safety, high anti-jamming property. The performance of the 16kbps and 9.6kbps speech codec is very excellent, the technology of 4.8kbps speech codec is also successful. The performance of 2.4kbps speech codec is poorer than 4.8kbps and better than 1.2kbps.So in the future, the emphasis of low rate speech codec research is the 2.4kbps speech codec.The arithmetic and construct of low rate speech codec is becoming more and more complicated. A lot of mid-rate speech codec technologies used in low rate speech codec. For example, MELP (mix excited linear predictor) 2.4kbps speech codec, the speech codec standard of 98 federal American. It is a very excellent low rate speech codec. It based on LPC, adopted many new technologies, its performance even exceeded mid-low rate speech codec (4.8kbps).To improve its performance we will adapt it.The improvement of the codec and my work are listed as below:(1)Analyse the speech signal and find the properties of the transition speech frame. Set the value of parameters to judge the transition speech frame.(2)Cut the transition speech frame into two smaller frames, encode and decode them independently. So it will avoid the error produced by classing the transition frame into V/UV frame.(3)Adapt the codec's code book, using two code books, the voiced code book and the unvoiced code book. So it can enhance the SNR by increasing the volume of the code book when the calculation isn't increased.(4)Adapt the bit allotion to fit the improvement.(5)Analyse the result of the experiment.