Hybrid subband coder/decoder method and apparatus
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United States of America Patent
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Nov 11, 1986
Grant Date -
N/A
app pub date -
Oct 17, 1984
filing date -
Oct 17, 1984
priority date (Note) -
Expired
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Abstract
The subband channels of a subband coder/decoder utilize different encoding/decoding algorithms so as to maximize overall signal transmission quality using a digital signal processor having limited digital memory capability. In the exemplary embodiment, a digitized 180-2900 Hz voice band signal is divided into four octave-spaced subbands. The highest frequency subband (1450-2900 Hz) is encoded/decoded using a block companded pulse code modulation (BCPCM) algorithm while each of the lower frequency subbands is encoded/decoded using an adaptive pulse code modulation (APCM) or an adaptive differential pulse code modulation (ADPCM) algorithm. The resulting 'hybrid' vocoder tends to maximize the quality of transmitted voice signals while yet permitting implementation within constrained digitial memory capacity and/or constrained transmission channel bandwidth.
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