With developing rapidly in modem communication and multi-media communication, a higher demand for information compression is put forward. In speech compression field, the current standards of speech coding no longer meet the demands of some applications. It becomes a more and more urgent task to try to find new methods and algorithms of speech coding and to publish new standards of speech coding. For two applications of wide-band speech coding (one is used a information inquiring system, and another is used a multi-media communication system), this paper presents two different wide-band speech coding schemes by using current popular algorithms of speech coding to try to attain the rate at or below which the new standards will request. This paper also uses the theory and techniques of Wavelets Transform to detect some parameters of speech signal, and gets good results. All work is as follows: 1. In this paper, the study emphasis on the algorithm Code Excited Linear Prediction (CELP), especially on the kernel techniques such as Linear Prediction Analysis, Construction of Code-Book, Code-Book Search and Perceptual Weighting. Author completes the software implement of CELP algorithm, and expands it to wide-band speech coding. 2. For the application of information inquiring system, the paper presents a Multimode and Variable-Rate Coding Algorithm Based on Splitting Band. The average rate attains below 7kb/s. Considering the special features of the code- store-playback system, the main features of the algorithm are: · By comparing the energy and short-term spectrum parameters of two neighboring frames, author designs a Voice Activity Detector (VAD) to detect efficiently the voice and the silence frames. · The unvoiced and the voiced (U/V) frames are detected efficiently by using the short-term energy and short-term zero-crossings. · According to the techniques of VAD and U/V Detecting and the special features of the speech signal of different spectrum bands and different frames. author designs a Multimode and Variable-Rate CELP Coding Algorithm. The algorithm makes the rate reduced deeply. · For the high and low bands, the coding scheme uses different perceptual weighting filter to attain the better results of perception of human ear. · For the National "863" Project --- "multi-media communication system" , this paper presents a wideband speech coding scheme which is suitable for the coding-transmission-decoding system~ In this coding scheme, author adopts the improved CELP algorithm for the low band, and adopts respectively two algorithms for the high band as follows: ~ 2-bit ADPCM algorithm ~ a ADM coder which have a 10-tap adaptive predictor. It attains a good S/N rate. Finally, the coding schemes attains respectively two rates --- 20.6kb/s and 3.6kb/s. · U
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