Studies On Speech Coding At Low Rates

With the development of communication technology and the improvement of the speech transmit technology in real time based on Internet, the high request to transmission efficiency and memory capacity of the speech is needed. One of the mains way to solve these problems is the speech coding.In the study of speech coding in present, The Mixed Excitation Linear Prediction (MELP) is a kind of relatively good method. The MELP Vocoder is the new Federal Standard speech coder. It was selected by the United States Department of Defense Digital Voice Processing Consortium (DDVPC). The MELP Vocoder is based on the traditional LPC parametric model, but also includes four additional features. These are mixed-excitation, aperiodic pulses, pulse dispersion, and adaptive spectral enhancement. So the MELP Vocoder can produce more natural sounding speech.With a analysis to MELP coding arithmetic, a speech codec scheme in software is presented in this paper. Carry on emulation to MELP standard, realize that the compression of the pronunciation file is solved and pressed. First this thesis sample to wav file ,carry on the speech to analyze and draws with the parameter to the speech data of every frame. These parameter include pitch, bpvc, jitter , LPC, etc. Then, these parameters will be quantized by MSVQ technology. Last these parameters will be decoded in the decoder.