Method and apparatus for encoding speech
DCFirst Claim
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1. A speech encoder comprising:
- Fourier transform means for performing a Fourier transform of a window of speech with formants to generate a Fourier transform spectrum;
normalizing means for defining from the Fourier transform spectrum at least one curve of different magnitudes approximating different magnitudes of the Fourier transform spectrum across the spectrum, for digitally encoding the at least one defined curve and for defining the Fourier transform spectrum relative to the at least one defined curve to provide a normalized spectrum; and
means for encoding at least a portion of the normalized spectrum.
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Abstract
In a speech encoder a Fourier transform of the speech is provided. The Fourier transform is equalized by normalizing the spectrum coefficients to a curve which approximates the shape of the spectrum. Both the curve and the equalized spectrum are encoded. Preferably, only a baseband of the normalized spectrum is encoded and that baseband is repeated in the decoder. The spectrum is normalized by scaling different regions (subbands) of the spectrum differently to flatten the spectrum.
82 Citations
29 Claims
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1. A speech encoder comprising:
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Fourier transform means for performing a Fourier transform of a window of speech with formants to generate a Fourier transform spectrum; normalizing means for defining from the Fourier transform spectrum at least one curve of different magnitudes approximating different magnitudes of the Fourier transform spectrum across the spectrum, for digitally encoding the at least one defined curve and for defining the Fourier transform spectrum relative to the at least one defined curve to provide a normalized spectrum; and means for encoding at least a portion of the normalized spectrum. - View Dependent Claims (2, 3, 4, 5, 6, 24)
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7. A speech encoder comprising:
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means for sampling a speech signal; an analog to digital converter for providing digital representations of the speech samples; a preemphasis filter; Fourier transform means for performing a Fourier transform of a window of digital speech samples to generate a Fourier transform spectrum; means for determining the maximum magnitude of the Fourier transform spectrum within each of a plurality of regions of the spectrum; means for digitally encoding the maximum magnitude of each region; means for dividing each coefficient of the Fourier spectrum in each region by the maximum magnitude of each region to provide a first set of normalized outputs; means for determining the maximum magnitude of the first set of normalized outputs in each of a plurality of subregions of the spectrum; means for digitally encoding the maximum magnitude of each subregion; means for dividing each output of the first set of normalized outputs by the maximum magnitude of each subregion to provide a second set of normalized outputs; and means for encoding a baseband of the second set of normalized outputs.
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8. A method of encoding speech comprising:
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performing a Fourier transform of a window of speech with formants to generate a Fourier transform spectrum; providing a normalized spectrum by defining from the Fourier transform spectrum at least one curve of different magnitudes approximately different magnitudes of the Fourier transform spectrum across the spectrum, digitally encoding the at least one defined curve and defining the Fourier transform spectrum relative to the at least one defined curve; and encoding at least a portion of the normalized spectrum. - View Dependent Claims (9, 10, 11, 12, 13, 25)
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14. A speech encoder comprising:
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transform means for performing a transform of an incoming speech signal with formants to generate a transform spectrum which varies significantly in magnitude across the spectrum; equalizing means for modifying the transform spectrum to provide a substantially flat spectrum and for encoding a function derived from the transform spectrum by which the transform spectrum is modified; and means for encoding at least a portion of the equalized spectrum. - View Dependent Claims (15, 16, 17, 26)
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18. A speech encoder comprising:
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transform means for performing a transform of a window of speech with formants to generate a transform spectrum; normalizing means for defining a magnitude relative to each of a plurality of regions of the transform spectrum and for scaling each coefficient of the transform spectrum, in each region of at least a portion of the spectrum, to the defined magnitude of the region of provide a normalized spectrum; and means for encoding the defined magnitudes and at least a portion of the normalized spectrum. - View Dependent Claims (19, 27)
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20. A method of encoding speech comprising:
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performing a transform of an incoming speech signal to generate a transform spectrum which varies significantly in magnitude across the spectrum; modifying the transform spectrum by a function derived from the transform spectrum to provide a substantially flat spectrum; and encoding the function derived from the transform spectrum by which the transform spectrum is modified and encoding at least a portion of the modified spectrum. - View Dependent Claims (21, 23, 28)
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22. A method of encoding speech comprising:
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performing a transform of a window of speech with formants to generate a transform spectrum; defining a magnitude relative to each of a plurality of regions of the transform spectrum and scaling each coefficient of the transform spectrum, in each region of at least a portion of the spectrum, to the defined magnitude of the region; and encoding the defined magnitudes and at least a portion of the scaled coefficients of the transform spectrum. - View Dependent Claims (29)
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Specification