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Digital encoder with dynamic quantization bit allocation

  • US 5,664,056 A
  • Filed: 07/08/1994
  • Issued: 09/02/1997
  • Est. Priority Date: 08/02/1991
  • Status: Expired due to Term
First Claim
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1. A digital encoding apparatus for compressing a digital input signal to provide a compressed output signal, the apparatus comprising:

  • frequency dividing means for receiving the digital input signal and for dividing the digital input signal into a plurality of frequency ranges;

    time dividing means for dividing in time at least one of the frequency ranges of the digital input signal into a plurality of blocks;

    orthogonal transform means for orthogonally transforming each block to provide a plurality of spectral coefficients;

    means for grouping by frequency the plurality of spectral coefficients from the orthogonal transform means into critical bands, each critical band having a band energy and a band frequency;

    bit allocation pattern selecting means for selecting a predetermined bit allocation pattern from a plurality of predetermined bit allocation patterns;

    first bit allocating means for allocating a total number of fixed bits among the critical bands to allocate to each critical band a number of fixed bits for quantizing each spectral coefficient in the critical band, the number of fixed bits allocated to each critical band being determined according to the selected predetermined bit allocation pattern;

    second bit allocating means for allocating a total of number of variable bits among the critical bands to allocate to each critical band a number of variable bits for quantizing each spectral coefficient in the critical band, the number of variable bits allocated to each critical band being determined according to the band energy of the critical band; and

    means for quantizing each spectral coefficient in each band using a number of bits equal to a sum of the number of fixed bits allocated for quantizing each spectral coefficient in the critical band and the number of variable bits allocated for quantizing each spectral coefficient in the critical band, the spectral coefficients in at least one of the critical bands being quantized using a number of fixed bits greater than zero and a number of variable bits greater than zero.

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