Linear predictive codeword excited speech synthesizer
First Claim
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1. A linear predictive codeword excited speech synthesizer comprising:
- linear predictive code analysis means for receiving an input speech signal and generating therefrom a set of linear predictive filter coefficients;
codeword selection means responsive to said linear predictive code analysis means for generating a codeword index;
inverse filter means responsive to said input speech signal and said linear predictive code analysis means for generating a residual speech signal output;
pitch detector means responsive to said inverse filter means for generating pitch lag and pitch tap gain output signals;
frame buffer means for receiving and storing samples of said input speech signal and said residual speech signal output;
pitch epoch position detector means responsive to said pitch detector means for operating on stored input and residual speech signals in said frame buffer so as to detect a point of maximum excitation over a pitch cycle;
gain estimator means for generating a gain output signal in response to segments of said stored input and residual speech signals in said frame buffer means; and
means for transmitting said linear predictive filter coefficients, said codeword index, said pitch lag and pitch tap gain output signals, and said gain output signal.
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Abstract
A linear predictive codeword excited speech synthesizer performs a voiced/unvoiced decision to determine the type of excitation to be supplied to a synthesis filter. The synthesizer selects the excitation for voiced speech from a codebook, using an analysis-by-synthesis technique in which the transfer function of a linear predictive coefficient synthesis filter closely resembles the gross spectral shape of the input speech signal. By pitch-periodic repetition of the selected codebook vector, a high quality synthetic speech output is generated.
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Citations
6 Claims
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1. A linear predictive codeword excited speech synthesizer comprising:
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linear predictive code analysis means for receiving an input speech signal and generating therefrom a set of linear predictive filter coefficients; codeword selection means responsive to said linear predictive code analysis means for generating a codeword index; inverse filter means responsive to said input speech signal and said linear predictive code analysis means for generating a residual speech signal output; pitch detector means responsive to said inverse filter means for generating pitch lag and pitch tap gain output signals; frame buffer means for receiving and storing samples of said input speech signal and said residual speech signal output; pitch epoch position detector means responsive to said pitch detector means for operating on stored input and residual speech signals in said frame buffer so as to detect a point of maximum excitation over a pitch cycle; gain estimator means for generating a gain output signal in response to segments of said stored input and residual speech signals in said frame buffer means; and means for transmitting said linear predictive filter coefficients, said codeword index, said pitch lag and pitch tap gain output signals, and said gain output signal. - View Dependent Claims (2, 3, 4, 5)
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6. A method for operating a linear predictive codeword excited speech synthesizer, said synthesizer including linear predictive code analysis means for receiving an input speech signal and generating therefrom a set of linear predictive filter coefficients, an all-pole linear predictive coefficient synthesis filter responsive to said linear predictive code analysis means for producing a filter transfer function that closely resembles a gross spectral shape of the input speech signal, and a codebook for providing a selected output signal, said method comprising:
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analyzing the input speech signal to produce said set of linear predictive filter coefficents; applying said linear predictive filter coefficents to said synthesis filter to generate said filter transfer function; searching said codebook to produce an output signal therefrom; muItiplying said output signal from said codebook by a gain factor to generate an excitation sequence input signal for said synthesis filter; subtracting the output signal of said synthesis filter from a speech samples input signal to produce a codeword index; choosing a new excitation codeword at a start of each frame of voiced speech, in synchronism with an output pitch period; and exciting said synthesis filter with a first P samples of said codeword, where P is the fundamental or pitch period of the input speech signal, the P samples being repeatedly played out to said synthesis filter to create a synthetic voiced output signal.
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Specification