Predictive speech signal coding with reduced noise effects
AssigneeBell Telephone Laboratories, Incorporated
InventorsBishnu S. Atal, Manfred R. Schroeder
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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.
Claims14
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.
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.
Dependencies are inferred from the claim text.