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UBC Theses and Dissertations

Speech bandwidth compression using a time transformation method Crowson, Donald Beattie


This thesis is concerned with the development of a slope-feedback coder, the purpose of which is to reduce the bandwidth required for the transmission of telephone-quality speech. Three similar coders, which operate separately on each of the three principal formants in speech, are required. The coding results in a reduction in the speech bandwidth from 3200 cps to 500 cps; the corresponding channel-capacity required is reduced from 32,000 bits per second to 6,200 bits per second. Theoretical statements of the performance of the coder are given showing how it transforms some stylised input signals (e.g. ramp and sinewave). From these statements, it is shown that: a) a single channel for each coder leads to very inferior performance - it is shown that two channels are required, and this gives good performance using much the same bandwidth; b) the signal-to-noise ratio required is moderate. A slope-feedback coder has been constructed, and a technical description of this apparatus is given. Experimental tests of the coder operating on simulated formants justify the theoretical predictions to within a root-mean-square error of twelve percent. This error decreases to six percent if those errors which are most subject to apparatus error are not considered.

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