A mixed prototype waveform/CELP coder for sub 3 kbit/s
- 1 January 1993
- conference paper
- Published by Institute of Electrical and Electronics Engineers (IEEE)
- Vol. 2, 175-178 vol.2
- https://doi.org/10.1109/icassp.1993.319262
Abstract
CELP (code-excited linear prediction) analysis-by-synthesis speech coders do not make a distinction between voiced and unvoiced speech frames. For sub-3 kbit/s coding it is necessary to separate unvoiced and voiced frames and code-voiced speech using an inherently periodic scheme. The authors address these problems by using a prototype waveform coder for voiced frames while retaining a CELP algorithm for unvoiced frames. For voiced speech a single residual prototype is selected to represent a section of 25 ms. Prototypes are interpolated across the frame to provide a smooth evolution of amplitude and harmonic content. Two coding schemes for the prototypes are discussed: a pitch harmonic scheme operating in the DFT (discrete Fourier transform) domain and an impulsive codebook time-domain technique. Unvoiced frames are coded using a standard CELP architecture excluding the adaptive codebook search. The overall bit rate using either of the voiced frame coding algorithms is shown to be sub-3 kbit/s for good communications quality speech.Keywords
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