Research On High Quality Waveform Interpolation Speech Coding At 2kb/s

Speech coding, which generally refers to the process of reducing the number of bits required for adequately representing speech signals in digital form, is one of the most important and fundamental function in modern digital speech communication systems. At present, speech coding technologies at above 8kb/s have already been standardized and achieved toll-quality. There is an ongoing standardization effort conducted by ITU-T for a 4kb/s speech coder with toll-quality. But with the rapid advancement of personal computer and international network, it's urgent to need a kind of speech coder at 2kb/s with communication quality in the area of mobile communications, multimedia communications and computer communications. Therefore, how to achieve communication quality at 2kb/s is a very important research issue. This dissertation presents a high quality Waveform Interpolation (WI) speech coding algorithm at 2kb/s based on the Characteristic Waveform Interpolation (CWI) algorithm. The main research results are as follows: (1) Two kinds of vector quantization (VQ) methods of line spectrum frequency (LSF) parameters are proposed. An efficient quantization method of LSF parameters is proposed based on second order temporal decomposition (TD) model by using the LSF ordering property. Experimental results show that a relative low spectral distortion and high average algorithm delay can be obtained at below 500b/s. So we quantize LSF parameters each frame to overcome the shortcoming of high delay. The Predictive Simultaneous Joint Muli-stage Split Vector Quantization (PSJ_MSVQ) scheme at 800b/s is designed by using the correlation of LSF parameters between frames and inter frames. The vector quantizer achieves an average spectral distortion of less than 1dB at 20 bits/frame with low computational complexity and storage requirements. (2) An algorithm of pitch detection for WI coding model is presented. Firstly, a pitch detection algorithm based on the Dyadic Wavelet Transform and the Normalized AutoCorrelation Function (DWT_NACF_PDA) is proposed. Compared with the normalized autocorrelation-based pitch detection algorithm in ITU-T G.729 standard, the DWT_NACF_PDA has a lower pitch-estimation error and computational complexity. After that, a pitch detection algorithm based on the Dyadic Wavelet Transform and the Normalized Cross-Correlation Function (DWT_NCCF_PDA) is...