|Author:||Wong, Chi-keung Julian|
|Title:||Coding of speech at 16 kbit/s using low-delay code excited linear prediction (LD-CELP)|
|Subject:||Speech processing systems|
Signal processing -- Digital techniques
Hong Kong Polytechnic -- Dissertations
|Department:||Department of Electronic Engineering|
|Pages:||76 leaves : ill. ; 30 cm|
|Abstract:||This thesis presents herewith a Low-Delay Code-Excited Linear Prediction (LD-CELP) speech coder which has been standardized in 1992 as a CCITT G Series Recommendation for universal applications of speech coding at 16 kbit/s. Low-Delay CELP coder has a performance equivalent or better than G.721 (32 kbit/s ADPCM) and meets all the speech quality requirements set by CCITT Study Group XV. The objectives of this thesis are to simulate the Low-Delay CELP speech coder in high level language (Turbo C Language) and to evaluate the speech quality by using objective measures in time and frequency domains. The algorithms of conventional CELP and Low-Delay CELP coders and concepts related to Low-delay CELP (including perceptual weighting filter, synthesis filter, excitation gain adaptation, excitation VQ codebook and adaptive postfilter) are described. A model of burst-noise channel is used for simulation. The simulation model is operated on coded speech files to evaluate the effects of speakers, input level variations, burst noise and codeword corruptions. To access the speech quality, objective measures such as segmental signal-to-noise ratio for waveform distortion measure; and LPC cepstrum distance measure for frequency spectrum distortion measure are employed.|
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