Predictive speech signal coding with reduced noise effects
First Claim
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1. A predictive speech signal communication system comprising apparatus (135) for analyzing a speech signal in selected time intervals to generate a set of formant related prediction parameter signals for each interval;
- circuitry (107,109) jointly responsive to said speech signal and said formant related prediction parameter signals for producing a signal representative of the difference between said speech signal and its predicted value;
a modifying circuit (137) for modifying said difference representative signal;
a quantizer (111) responsive to said modified difference signal for generating a quantized signal; and
a subtracter circuit (113) for forming a quantizing error signal corresponding to the difference between said quantized and unquantized modified difference signal CHARACTERIZED IN THAT said modifying circuit (137) is jointly responsive to said formant related prediction parameter signals, said quantizing error signal and said difference signal to concentrate the quantizing error in the formant portions of said speech signal spectrum whereby the quantizing error is masked by said speech signal formants.
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Abstract
A predictive speech signal processor features an adaptive filter in a feedback network around the quantizer. The adaptive filter essentially combines the quantizing error signal, the formant related prediction parameter signals and the difference signal to concentrate the quantizing error noise in spectral peaks corresponding to the time-varying formant portions of the speech spectrum so that the quantizing noise is masked by the speech signal formants.
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Citations
14 Claims
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1. A predictive speech signal communication system comprising apparatus (135) for analyzing a speech signal in selected time intervals to generate a set of formant related prediction parameter signals for each interval;
- circuitry (107,109) jointly responsive to said speech signal and said formant related prediction parameter signals for producing a signal representative of the difference between said speech signal and its predicted value;
a modifying circuit (137) for modifying said difference representative signal;
a quantizer (111) responsive to said modified difference signal for generating a quantized signal; and
a subtracter circuit (113) for forming a quantizing error signal corresponding to the difference between said quantized and unquantized modified difference signal CHARACTERIZED IN THAT said modifying circuit (137) is jointly responsive to said formant related prediction parameter signals, said quantizing error signal and said difference signal to concentrate the quantizing error in the formant portions of said speech signal spectrum whereby the quantizing error is masked by said speech signal formants. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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7. A predictive speech signal communication system according to claim 6 further comprising means (203, 205, 217) responsive to said quantized signal for producing an excitation signal and means (215, 219, 207) jointly responsive to said excitation signal and said formant related predictive parameter signals for forming a replica of said speech signal CHARACTERIZED IN THAT said excitation signal producing means (213, 217, 205) includes a voice periodicity predictor (217) responsive to said quantized signal, said pitch related prediction parameter signals and said pitch period related signal for forming a signal corresponding to the predicted value of said difference signal and means (205) for combining said predicted value of said difference signal with said quantized signal.
- circuitry (107,109) jointly responsive to said speech signal and said formant related prediction parameter signals for producing a signal representative of the difference between said speech signal and its predicted value;
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8. A method for processing a speech signal comprising the steps of analyzing said speech signal in selected intervals to generate a set of formant related prediction parameter signals for each interval;
- producing a signal representative of the difference between the present speech signal and its predicted value responsive to said speech signal and said formant related prediction parameter signals;
modifying said difference signal;
quantizing said modified difference signal; and
forming a quantizing error signal corresponding to the difference between said quantized and unquantized modified difference signals CHARACTERIZED IN THAT the modification of said difference signal includes combining said formant related prediction parameter signals, said quantizing error signal and said difference signal to concentrate the quantizing error in the formant portions of said speech signal spectrum so that the quantizing error is masked by said speech signal formants. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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14. A method for processing a speech signal according to claim 13 further including the steps of producing an excitation signal responsive to said quantized signal and forming a replica of said speech signal by combining said excitation signal with said formant related prediction parameter signals CHARACTERIZED IN THAT said excitation producing step comprises forming a signal corresponding to the predicted value of said difference signal from the preceding portion of said quantized signal, said pitch related prediction parameter signals b1, b2, b3 and said pitch related signal m and combining the present quantized signal with said predicted value of difference signal.
- producing a signal representative of the difference between the present speech signal and its predicted value responsive to said speech signal and said formant related prediction parameter signals;
Specification