Fast frequency-domain pitch estimation
First Claim
1. A method for estimating a pitch frequency of a speech signal, comprising:
- computing a first transform of the speech signal to a frequency domain over a first time interval;
computing a second transform of the speech signal to the frequency domain over a second time interval, which contains the first time interval; and
estimating the pitch frequency of the speech signal responsive to the first and second transforms, wherein the first and second transforms comprise Short Time Fourier Transforms.
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Accused Products
Abstract
A method for estimating a pitch frequency of an audio signal includes computing a first transform of the signal to a frequency domain over a first time interval, and computing a second transform of the signal to the frequency domain over a second time interval, which contains the first time interval. A line spectrum of the signal is found, based on the first and second transforms, the spectrum including spectral lines having respective line amplitudes and line frequencies. A utility function that is periodic in the frequencies of the lines in the spectrum is then computed. This function is indicative, for each candidate pitch frequency in a given pitch frequency range, of a compatibility of the spectrum with the candidate pitch frequency. The pitch frequency of the speech signal is estimated responsive to the utility function.
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Citations
52 Claims
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1. A method for estimating a pitch frequency of a speech signal, comprising:
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computing a first transform of the speech signal to a frequency domain over a first time interval;
computing a second transform of the speech signal to the frequency domain over a second time interval, which contains the first time interval; and
estimating the pitch frequency of the speech signal responsive to the first and second transforms, wherein the first and second transforms comprise Short Time Fourier Transforms. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method for estimating a pitch frequency of a speech signal, comprising:
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finding a line spectrum of the speech signal, the spectrum comprising spectral lines having respective line amplitudes and line frequencies;
computing a utility function, which is indicative, for each candidate pitch frequency in a given pitch frequency range, of a compatibility of the spectrum with the candidate pitch frequency, the utility function comprising at least one influence function that is periodic in a ratio of the frequency of one of the spectral lines to the candidate pitch frequency; and
estimating the pitch frequency of the speech signal responsive to the utility function. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17)
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18. A method for estimating a pitch frequency of a speech signal, comprising:
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finding a line spectrum of the signal, the spectrum comprising spectral lines having respective line amplitudes and line frequencies;
computing a utility function that is periodic in the frequencies of the lines in the spectrum, which function is indicative, for each candidate pitch frequency in a given pitch frequency range, of a compatibility of the spectrum with the candidate pitch frequency; and
estimating the pitch frequency of the speech signal responsive to the utility function, wherein computing the utility function comprises computing at least one influence function that is periodic in a ratio of the frequency of one of the spectral lines to the candidate pitch frequency, and wherein computing the at least one influence function comprises computing a function of the ratio having maxima at integer values of the ratio and minima therebetween, and wherein computing the function of the ratio comprises computing values of a piecewise linear function c(f), having a maximum value in a first interval surrounding f=0, a minimum value in a second interval surrounding f=1/2, and a value that varies linearly in a transition interval between the first and second intervals.
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19. A method for estimating a pitch frequency of a speech signal, comprising:
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finding a line spectrum of the speech signal, the spectrum comprising spectral lines having respective line amplitudes and line frequencies;
computing a utility function that is periodic in the frequencies of the lines in the spectrum, which function is indicative, for each candidate pitch frequency in a given pitch frequency range, of a compatibility of the spectrum with the candidate pitch frequency; and
estimating the pitch frequency of the speech signal responsive to the utility function, wherein computing the utility function comprises computing at least one influence function that is periodic in a ratio of the frequency of one of the spectral lines to the candidate pitch frequency, and wherein computing the at least one influence function comprises computing respective influence functions for multiple lines in the spectrum, and wherein computing the utility function comprises computing a superposition of the influence functions, and wherein the respective influence functions comprise piecewise linear functions having break points, and wherein computing the superposition comprises calculating values of the influence functions at the break points, such that the utility function is determined by interpolation between the break points. - View Dependent Claims (20)
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21. A method for estimating a pitch frequency of a speech signal, comprising:
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finding a line spectrum of the speech signal, the spectrum comprising spectral lines having respective line amplitudes and line frequencies;
computing a utility function that is periodic in the frequencies of the lines in the spectrum, which function is indicative, for each candidate pitch frequency in a given pitch frequency range, of a compatibility of the spectrum with the candidate pitch frequency; and
estimating the pitch frequency of the speech signal responsive to the utility function, wherein computing the utility function comprises computing at least one influence function that is periodic in a ratio of the frequency of one of the spectral lines to the candidate pitch frequency, and wherein computing the at least one influence function comprises computing respective influence functions for multiple lines in the spectrum, and wherein computing the utility function comprises computing a superposition of the influence functions, and wherein computing the respective influence functions comprises performing the following steps iteratively over the lines in the spectrum;
computing a first influence function for a first line in the spectrum;
responsive to the first influence function, identifying one or more intervals in the pitch frequency range that are incompatible with the spectrum;
defining a reduced pitch frequency range from which the one or more intervals have been eliminated; and
computing a second influence function for a second line in the spectrum, while substantially restricting computation of the second influence function to pitch frequencies within the reduced range. - View Dependent Claims (22, 23, 24)
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25. Apparatus for estimating a pitch frequency of a speech signal, comprising an audio processor, which is adapted to compute a first transform of the speech signal to a frequency domain over a first time interval and a second transform of the speech signal to a frequency domain over a second time interval, which contains the first time interval, and to estimate the pitch frequency of the speech signal responsive to the first and second frequency transforms,
wherein the first and second transforms comprise Short Time Fourier Transforms.
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28. Apparatus for estimating a pitch frequency of a speech signal, comprising an audio processor, which is adapted to compute a first transform of the speech signal to a frequency domain over a first time interval and a second transform of the speech signal to a frequency domain over a second time interval, which contains the first time interval, and to estimate the pitch frequency of the speech signal responsive to the first and second frequency transforms,
wherein the first time interval comprises a current frame of the speech signal, and the second time interval comprises the current frame and a preceding frame, and wherein the processor is adapted to compute the second transform by combining the first transform with a transform computed over the preceding frame, and wherein the transforms generate respective spectral coefficients, and wherein the processor is adapted to apply a phase shift to the coefficients generated by the transform computed over the preceding frame and to add the phase-shifted coefficients to the coefficients generated by the transform computed over the first time interval.
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30. Apparatus for estimating a pitch frequency of a speech signal, comprising an audio processor, which is adapted to compute a first transform of the speech signal to a frequency domain over a first time interval and a second transform of the speech signal to a frequency domain over a second time interval, which contains the first time interval, and to estimate the pitch frequency of the speech signal responsive to the first and second frequency transforms,
wherein the processor is adapted to derive first and second line spectra of the signal from the first and second transforms, respectively, and to determine the pitch frequency based on the line spectra.
- 34. Apparatus for estimating a pitch frequency of a speech signal, comprising an audio processor, which is adapted to find a line spectrum of the speech signal, the spectrum comprising spectral lines having respective line amplitudes and line frequencies, to compute a utility function, which is indicative, for each candidate pitch frequency in a given pitch frequency range, of a compatibility of the spectrum with the candidate pitch frequency, the utility function comprising at least one influence function that is periodic in a ratio of the frequency of one of the spectral lines to the candidate pitch frequency, and to estimate the pitch frequency of the speech signal responsive to the periodic function.
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48. Apparatus for estimating a pitch frequency of a speech signal, comprising an audio processor, which is adapted to find a line spectrum of the speech signal, the spectrum comprising spectral lines having respective line amplitudes and line frequencies, to compute a utility function that is periodic in the frequencies of the lines in the spectrum, which function is indicative, for each candidate pitch frequency in a given pitch frequency range, of a compatibility of the spectrum with the candidate pitch frequency, and to estimate the pitch frequency of the speech signal responsive to the periodic function,
wherein the utility function comprises at least one influence function that is periodic in a ratio of the frequency of one of the spectral lines to the candidate pitch frequency, and wherein the at least one influence function comprises a function of the ratio having maxima at integer values of the ratio and minima therebetween, and wherein the at least one influence function comprises a piecewise linear function c(f), having a maximum value in a first interval surrounding f=0, a minimum value in a second interval surrounding f=1/2, and a value that varies linearly in a transition interval between the first and second intervals.
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49. A computer software product, comprising a computer-readable storage medium in which program instructions are stored, which instructions, when read by a computer receiving a speech signal, cause the computer to compute a first transform of the speech signal to a frequency domain over a first time interval and a second transform of the speech signal over a second time interval to the frequency domain, which contains the first time interval, and to estimate the pitch frequency of the speech signal responsive to the first and second transforms,
wherein the first and second transforms comprise Short Time Fourier Transforms.
- 51. A computer software product, comprising a computer-readable storage medium in which program instructions are stored, which instructions, when read by a computer receiving a speech signal, cause the computer to find a line spectrum of the speech signal, the spectrum comprising spectral lines having respective line amplitudes and line frequencies, to compute a utility function, which is indicative, for each candidate pitch frequency in a given pitch frequency range, of a compatibility of the spectrum with the candidate pitch frequency, the utility function comprising at least one influence function that is periodic in a ratio of the frequency of one of the spectral lines to the candidate pitch frequency, and to estimate the pitch frequency of the speech signal responsive to the periodic function.
Specification