Dynamic bit allocation subband excited transform coding method and apparatus
DCFirst Claim
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1. A speech coding system comprising:
- transform means for performing a discrete transform of a window of speech to generate a discrete transform spectrum of coefficients comprising a plurality of subbands of coefficients;
envelope defining and encoding means for defining an approximate envelope of the discrete spectrum of coefficients in each of the plurality of subbands of coefficients and for encoding the defined envelope of each subband of coefficients;
means for scaling each spectrum coefficient relative to the encoded defined envelope of the respective subband of coefficients;
a plurality of quantizers having different bit lengths for encoding the scaled spectrum coefficients within each subband; and
means for determining a quantizer from the plurality of quantizers having different bit lengths, if any, to be used to encode the scaled spectrum coefficients of each subband within each window of speech wherein the selection of available quantizers used in successive windows is variable.
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Abstract
In an adaptive subband excited transform speech encoding system, a range of quantizers are available and are dynamically selected for each window of speech. The quantizers designated for individual subbands are determined to minimize mean squared error distortion in the recreated signal while using no more than a predetermined number of quantization bits per window of speech.
73 Citations
18 Claims
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1. A speech coding system comprising:
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transform means for performing a discrete transform of a window of speech to generate a discrete transform spectrum of coefficients comprising a plurality of subbands of coefficients; envelope defining and encoding means for defining an approximate envelope of the discrete spectrum of coefficients in each of the plurality of subbands of coefficients and for encoding the defined envelope of each subband of coefficients; means for scaling each spectrum coefficient relative to the encoded defined envelope of the respective subband of coefficients; a plurality of quantizers having different bit lengths for encoding the scaled spectrum coefficients within each subband; and means for determining a quantizer from the plurality of quantizers having different bit lengths, if any, to be used to encode the scaled spectrum coefficients of each subband within each window of speech wherein the selection of available quantizers used in successive windows is variable. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of coding speech comprising:
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performing a discrete transform of a window of speech to generate a discrete spectrum of coefficients comprising a plurality of subbands of coefficients; defining an approximate envelope of the discrete spectrum of coefficients in each of the plurality of subbands of coefficients and digitally encoding the defined envelope of each subband of coefficients; dynamically selecting a quantizer from a plurality of quantizers having different bit lengths for use with each subband of each window of speech to minimize distortion, the selection of available quantizers used in successive windows being variable and based on spectral power density of the window; scaling the coefficients within the subbands relative to the defined approximate envelopes of the subbands; and encoding each of the scaled coefficients within the subbands into a number of bits using the selected quantizer. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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Specification