Patent EP0592151A1 successfully refreshed from Google Patents.
EP0592151A1
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Time-frequency interpolation with application to low rate speech coding
Assignee: AT&T Inc
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Filing: 1993-09-30
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Granted: —
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Expires: 2013-09-30
Abstract
Abstract A method for high quality speech coding is disclosed which offers advantages over conventional CELP (code-excited linear predictive) algorithms for low rate coding. The method, Time-Frequency Interpolation (TFI), provides a perceptually advantageous framework for voiced speech processing. The general formulation of the TFI technique is described.
Inventors
- 👤 Yair Shoham
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-02 22:25
CPC Classifications
G; G10; G10L; G10L19/00; G10L19/02; G10L19/0212; G10L2019/0001; G10L2019/0012; G10L25/00; G10L25/93
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
81 words
A method of encoding a speech signal, said speech signal comprising a sequence of samples, wherein each of said samples is taken at a discrete point in time, said method comprising the steps of: forming a plurality of spectra, wherein each spectrum in said plurality of spectra is associated with a sample in said sequence of samples and wherein each spectrum is generated from a contiguous plurality of samples; decimating said plurality of spectra to form a set of decimated spectra.
Claim 2
Independent Claim
59 words
A method of decoding a coded speech signal, wherein said coded speech signal comprises a set of decimated spectra, said method comprising the steps of: interpolating said set of decimated spectra to form a complete spectrum sequence; inverse transforming said complete spectrum sequence to form a set of signals; windowing said set of signals to form a windowed signal.
Claim 3
Dependent Claim
13 words
The method of claim 2 wherein said step of interpolating comprises linear interpolation.
Claim 4
Dependent Claim
49 words
The method of claim 2 wherein each spectrum in said plurality of spectra comprises a set of coefficients, each coefficient in said set of coefficients having a magnitude component and phase component, and wherein said step of interpolating is applied non-linearly and separately to said magnitude and phase component.
Claim 5
Dependent Claim
23 words
The method of claim 1 wherein said plurality of spectra further comprises forming a reduce-sized parametric representation of said set of decimated spectra.
Claim 6
Dependent Claim
37 words
The method of claim 2 wherein said step of inverse transforming is according to the rule where y(n,m) is said set of signals, Y(n,K) is said complete spectrum sequence and c(m) is a discrete time scale function.
Claim 7
Independent Claim
191 words
A method for encoding a plurality of speech signals, wherein each of said speech signals comprises a sequence of samples occurring during a time frame and wherein said time frames are contiguous, said method comprising for each time frame the steps of: generating a plurality of parameters characterizing said speech signal; quantizing said parameters to form a set of quantized parameters; selecting an index associated with an entry in a codebook which entry best matches said quantized parameters in accordance with a first error measure; determining a pitch period for said speech signal; selecting an index associated with an entry in a codebook which entry best matches said pitch period in accordance with a second error measure; inverse filtering said speech signal to produce an excitation signal using filter parameters determined by said set of quantized parameters; transforming said excitation signal to form a first spectrum; modifying said first spectrum to form a modified spectrum; quantizing said modified spectrum to form a quantized modified spectrum; and selecting an index associated with an entry in a codebook which entry best matches said quantized modified spectrum in accordance with a third error measure.
Claim 8
Dependent Claim
28 words
The method of claim 7 wherein said step of forming a plurality of parameters comprises identifying characteristics of said speech signal indicating that the speech is voiced speech.
Claim 9
Dependent Claim
16 words
The method of claim 7 wherein said plurality of parameters are generated by linear predictive coding.
Claim 10
Dependent Claim
48 words
The method of claim 7 wherein said step of forming a plurality of parameters characterizing said speech signals comprises the steps of: identifying whether said speech signals represent voiced speech, and when said identifying fails to identify voiced speech, forming a second coded signal using alternative coding techniques.
Claim 11
Dependent Claim
15 words
The method of claim 10 wherein said alternative coding technique is code-excited linear predictive coding.
Claim 12
Dependent Claim
25 words
The method of claim 7 wherein said transforming is according to a discrete Fourier transform rule with a period approximately equal to said pitch period.
Claim 13
Dependent Claim
20 words
The method of claim 7 wherein said step of quantizing the modified spectrum is according to predictive weighted vector quantization.
Claim 14
Dependent Claim
83 words
The method of claim 7 further comprising the steps of: enchancing said modified spectrum; aligning said modified spectrum with the spectrum of a speech signal from a prior frame; interpolating between said modified spectrum and said spectrum of a speech signal from a prior frame to find spectra for other samples in said frame to yield a complete spectrum sequence; inverse transforming said complete spectrum sequence to yield a set of signals; and windowing said set of signals to yield a windowed signal.
Claim 15
Dependent Claim
124 words
The method of claim 7 further comprising the steps of: enhancing said modified spectrum; aligning said modified spectrum with the spectrum of a speech signal from a prior frame; inverse transforming said modified spectrum to yield a first signal, y (-1, m ) and inverse transforming said spectrum of said speech signal from said prior frame to yield a second signal, y ( N -1 ,m); linearly interpolating between said first signal and said second signal to yield a final signal, z ( m ), wherein said interpolation is according to the rule: z ( m )=α( m ) y (-1, m )+β( m ) y ( N -1, m ) where and where w ( n , m ) is a windowing function.
Claim 16
Independent Claim
198 words
A method for decoding a coded plurality of speech signals, said signals representing: a first index associated with an entry in a look-up table wherein said entry represents a plurality of parameters characterizing said speech signal, a second index associated with an entry in a second look-up table wherein said entry represents a pitch signal for said speech signal, and a third index associated with an entry in a third look-up table wherein said entry represents a spectrum of said speech signal, said method comprising the steps of: determining said parameters characterizing said speech signal based on said first index; determining said pitch signal based on said second index; determining said spectrum based on said third index; modifying and enhancing said spectrum to form a modified spectrum; aligning said modified spectrum with the spectrum of a speech signal from a prior frame; interpolating between said spectrum and the spectrum of a speech signal from a prior frame to yield a complete spectrum sequence; inverse transforming said second spectrum to yield a set of signals; windowing said set of signals to yield a windowed signal; and filtering said windowed signal, wherein said filter characteristics are determined by said parameters.
Claim 17
Independent Claim
213 words
A system for encoding a plurality of speech signals, wherein each of said speech signals comprises a sequence of samples occuring during a time frame and wherein said time frames are contiguous, said system comprising: means for generating a plurality of parameters characterizing said speech signal; means for quantizing said parameters to form a set of quantized parameters; means for selecting an index associated with an entry in a codebook which entry best matches said quantized parameters in accordance with a first error measure; means for determining a pitch period for said speech signal; means for selecting an index associated with an entry in a codebook which entry best matches said pitch period in accordance with a second error measure; means for inverse filtering said speech signal to produce an excitation signal, wherein said means for inverse filtering comprises a filter with filter parameters determined by said set of quantized parameters; means for transforming said excitation signal to form a first spectrum; means for modifying said first spectrum to form a modified spectrum; means for quantizing said modified spectrum to form a quantized modified spectrum; and means for selecting an index associated with an entry in a codebook which entry best matches said quantized modified spectrum in accordance with a third error measure.
Claim 18
Dependent Claim
84 words
The system of claim 17 further comprising: means for enchancing said modified spectrum; means for aligning said modified spectrum with the spectrum of a speech signal from a prior frame; means for interpolating between said modified spectrum and said spectrum of a speech signal from a prior frame to find spectra for other samples in said frame to yield a complete spectrum sequence; means for inverse transforming said complete spectrum sequence; and means for windowing said set of signals to yield a windowed signal.
Claim 19
Independent Claim
213 words
A system for decoding a coded plurality of speech signals, said signals representing: a first index associated with an entry in a look-up table wherein said entry represents a plurality of parameters characterizing said speech signal, a second index associated with an entry in a second look-up table wherein said entry represents a pitch signal for said speech signal, and a third index associated with an entry in a third look-up table wherein said entry represents a spectrum of said speech signal, said system comprising: means for determining said parameters characterizing said speech signal based on said first index; means for determining said pitch signal based on said second index; means for determining said spectrum based on said third index; means for modifying and enhancing said spectrum to form a modified spectrum; means for aligning said modified spectrum with the spectrum of a speech signal from a prior frame; means for interpolating between said spectrum and the spectrum of a speech signal from a prior frame to yield a complete spectrum sequence; means for inverse transforming said second spectrum to yield a set of signals; means for windowing said set of signals to yield a windowed signal; and means for filtering said windowed signal, wherein said filter characteristics are determined by said parameters.
References Cited (Backward Citations)
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