A high-gain DSI-ADPCM system
- 24 March 2005
- conference paper
- Published by Institute of Electrical and Electronics Engineers (IEEE)
- Vol. 4, 436-441
- https://doi.org/10.1109/icassp.1979.1170673
Abstract
This paper describes DSI-ADPCM system in which a digital speech interpolation (DSI) system is combined with an adaptive differential PCM (ADPCM). The speech detector in DSI detects speech signals above -51 dBm with 32 ms hangover time, and attains 36 % reduction of average activity of a trunk in the international long distance lines. The adaptive bit assignment to the voiced and unvoiced sounds is adopted to cope with the freeze-out condition. These facts result in a DSI gain of 3. Furthermore, the 4 bit encoding is applied to DSI output at ADPCM with 6 kHz sampling attaining an ADPCM gain of 2.6. While the frequency of PCM speech signal with 8 kHz sampling is shifted 250 Hz down to lower range before the conversion of the sampling frequency from 8 kHz to 6 kHz is made to avoid quality degradation. Thus the total gain of 7 is expected when DSI and ADPCM are incorporated, and has already been demonstrated by computer simulation with satisfactorily high quality of speech.Keywords
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