Vector Quantization In The Low-rate Voice Codecs

Speech communication is an important and indispensable service of different modern communication systems from the very time when the telephone was invented<, With the increasing of network use^ the integrating and diversifying of network service, the contradiction among bandwidth> system capacity and service quality are more and more obvious, traditional 64Kbps PCM speech coding can not satisfy the requirement of transmit bandwidth which is becoming more and more congested?So, How to reduce the bit-rate of speech without notably degrading its perceptual quality is a question placed at the front of the researchers.First, based on the discrete model of speech production, the paper tell the principle and technology of low bit-rate speech codec in brief; Second the subject of the paper is reached which is on VQ (Vector Quantization) in low bit-rate speech codec. In this section, the paper comes to basic concepts, ingredients and key sides of VQ. Then in combination with the previous theory, the VQ of last low bit-rate speech codec -ITU-T G.729 and AMR of 3G WCDMA taken into the objects, the paper analyses the VQ of LSP/LSF coefficients , pitch gain and algebraic-codebook gain.During my postgraduate study, I took part in the project - field implementation on DSP of AMR speech codec in 3G WCDMA, it gives me a chance of understanding the low bit-rate speech codec more deeply; and according to these modules which I implemented, it make me comprehend the VQ more accurately.