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US 5,694,521 AGranted
Variable speed playback system
AssigneeRockwell International Corporation
InventorsEyal Shlomot, Albert Achuan Hsueh
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Abstract
A variable speed playback system exploits multiple-period similarities within a residual signal, and includes multiple-period template matching which may be applied to alter the excitation periodical structure, and thereby increase or decrease the rate of speech playback. Embodiments of the present invention enable accurate fast or slow speech playback for store and forward applications without changing the pitch period of the speech. A correlated multiple-period similarity measure is determined for an excitation signal within a compressor/expander. The multiple-period similarity enables overlap-and-add expansion or compression by a rational ratio. Energy variations at the onset and offset portions of the speech may be weighted by energy-based adaptive weight windows.
Claims34
A system for providing fast and slow speed playback capabilities, operable on a linear predictive coding (LPC) excitation signal which is represented by a waveform including periodic and non-periodic portions, comprising:
- a signal compressor/expander for receiving and modifying the entire LPC excitation signal, wherein compression and expansion are performed according to a rational N-to-M ratio;
- means for segregating at least one set of variable-length templates within the LPC excitation signal, each template defining at least one segment of time representing part of the waveform of the LPC excitation signal;
- means for selecting a set of templates X.sub.ML and y.sub.ML having similar waveforms among the segregated variable-length templates, the selected set of templates including M segments of variable length L which provides a maximum amount of matching between X.sub.ML and y.sub.ML, wherein the length of templates X.sub.ML and y.sub.ML is determined according to M multiplied by L which is not dependent upon the periodicity of the waveform;
- means for compressing and expanding the LPC excitation signal for fast and slow playback, respectively, by overlapping and adding the selected set of templates X.sub.ML and y.sub.ML into at least one template having M segments, the M segments defining a modified excitation signal;
- a filter for filtering the modified excitation signal;
- and
- output means for outputting the filtered signal.
4 more elements
A store and retrieve system for providing fast and slow speed playback capabilities, operable on a linear predictive coding (LPC) excitation signal including periodic and non-periodic portions, comprising:
- a signal compressor/expander for receiving and modifying the entire LPC excitation signal, wherein compression and expansion are performed according to a rational N-to-M ratio, the signal compressor/expander including:
- means for selecting at least one set of templates within the LPC excitation signal, wherein each template in a set defines M segments of time which correspond to M segments in other templates within the set, wherein each segment has a variable length L,
- means for calculating the normalized correlation of each set of templates, such that as L varies, the normalized correlations of the sets of templates correspondingly vary,
- means for determining a value L.sup.* for which the normalized correlation among the sets of templates is maximized, such that an operational set of templates X.sub.ML* and y.sub.ML* is extracted, wherein the length of templates X.sub.ML* and y.sub.ML* is determined according to M multiplied by L which is not dependent upon the periodicity of the waveform,
- means for determining an energy of each segment in each template,
- means for calculating ratios of the energies of corresponding segments,
- means for constructing complementary windows according to the N-to-M ratio, the value of L.sup.*, and the ratios of the energies,
- means for multiplying the operational set of templates with the complementary windows to provide windowed templates,
- means for overlapping the windowed templates, and
- means for summing the overlapped windowed templates, wherein the summed templates represent a modified LPC excitation signal;
- an LPC synthesis filter for receiving the modified LPC excitation signal, and filtering the modified LPC excitation signal to yield a modified speech signal;
- and
- means for outputting the modified speech signal.
10 more elements
A method for providing fast and slow speed playback capabilities, operable on a linear predictive coding (LPC) excitation signal including periodic and non-periodic portions, comprising the steps of:
- receiving the LPC excitation signal;
- modifying the entire LPC excitation signal, wherein compression and expansion are performed according to a rational N-to-M ratio, including the steps of:
- selecting at least one set of templates within the LPC excitation signal, wherein each template in a set defines M segments of time which correspond to M segments in other templates within the set, wherein each segment has a variable length L,
- correlating each set of templates, such that as L varies, the correlations of the sets of templates correspondingly vary,
- determining a value L.sup.* for which the correlation among the sets of templates is maximized, such that an operational set of templates X.sub.ML* and y.sub.ML* is selected, wherein the length of templates X.sub.ML* and y.sub.ML* is determined according to M multiplied by L which is independent of the periodicity of the excitation signal,
- determining an energy of each segment in each template,
- calculating ratios of the energies of corresponding segments,
- constructing complementary windows according to the N-to-M ratio, the ratios of the energies, and L.sup.*,
- multiplying the operational set of templates with the complementary windows to provide windowed templates,
- overlapping the windowed templates, and
- summing the overlapped windowed templates, wherein the summed templates represent a modified LPC excitation signal;
- filtering the modified LPC excitation signal to yield a modified speech signal;
- and
- means for outputting the modified speech signal.
11 more elements
A system for providing fast and slow speed playback capabilities, operable on a linear predictive coding (LPC) excitation signal which is represented by a waveform, comprising:
- a signal compressor/expander for receiving and modifying the LPC excitation signal, wherein compression and expansion are performed according to a rational N-to-M ratio, the signal compressor/expander including:
- means for segregating at least one set of templates within the LPC excitation signal, each template defining at least one segment of time representing part of the waveform of the LPC excitation signal,
- selecting means for selecting a set of templates having similar waveforms, and
- combining means for compressing and expanding the LPC excitation signal for fast and slow playback, respectively, by combining the set of templates into a single template having M segments, which defines a modified excitation signal, wherein the combining means includes:
- means for calculating a correlation C.sub.ML of each set of templates, wherein each set of templates includes two templates, the at least one segment defined in each template having a variable length L, and the two templates defining the at least one segment are represented as X.sub.ML and y.sub.ML ;
- means for determining a value L.sup.* for which the correlation among the sets of templates is maximized according to:
- L.sup.* arg.sub.L max(C.sub.ML),
- such that templates X.sub.ML* and y.sub.ML* are selected according to the length L.sup.* of the templates for which the correlation is maximized;
- means for determining energy values of each corresponding segment in each template X.sub.ML* and y.sub.ML*, wherein the energy values are calculated for each corresponding segment k=0, . . . , M-1 as:
- ##EQU23## means for calculating ratios of the energies of corresponding segments, wherein the ratios of the energies of corresponding segments are determined by:
- ##EQU24## means for determining and applying weight coefficients of the ratios, wherein the weight coefficients of the ratios, for k=0, . . . , M-1, are determined by:
- ##EQU25## where w(k)=0, for E.sub.X (k).sup.* E.sub.y (k)=0, a filter for filtering the modified excitation signal;
- and output means for outputting the filtered signal.
10 more elements
A store and retrieve system for providing fast and slow speed playback capabilities, operable on a linear predictive coding (LPC) excitation signal, comprising:
- a signal compressor/expander for receiving and modifying the LPC excitation signal, wherein compression and expansion are performed according to a rational N-to-M ratio, the signal compressor/expander including:
- means for selecting at least one set of templates within the LPC excitation signal, wherein each template in a set defines M segments of time which correspond to M segments in other templates within the set, wherein each segment has a variable length L,
- means for calculating the normalized correlation of each set of templates, such that as L varies, the normalized correlations of the sets of templates correspondingly vary,
- means for determining a value L.sup.* for which the normalized correlation among the sets of templates is maximized, such that an operational set of templates X.sub.ML, and y.sub.ML* is found,
- means for determining an energy of each segment in each template,
- means for calculating ratios of the energies of corresponding segments,
- means for determining weight coefficients of the energy ratios, wherein the weight coefficients of the energy ratios, for k=0, . . . , M-1, are determined by:
- ##EQU30## where w(k)=0, for E.sub.x (k)*E.sub.y (k)=0. means for determining preliminary window amplitudes according to the N-to-M ratio and the value of L.sup.*, wherein the preliminary window amplitude as given as:
- ##EQU31## for k=0, . . , M-1 and i=0, . . . L.sup.* -1, means for constructing complementary windows according to the N-to-M ratio, the value of L.sup.*, and the ratios of the energies, wherein the complementary windows are constructed according to the N-to-M ratio, L.sup.*, the weight coefficients, the calculated energies, and the preliminary window amplitudes, such that for fast playback, the complementary windows are constructed according to:
- ##EQU32## and for slow playback, the complementary windows are constructed according to:
- ##EQU33## means for multiplying the operational set of templates with the complementary windows to provide windowed templates,
- means for overlapping the windowed templates, and
- means for summing the overlapped windowed templates, wherein the summed templates represent a modified LPC excitation signal;
- an LPC synthesis filter for receiving the modified LPC excitation signal, and filtering the modified LPC excitation signal to yield a modified speech signal;
- and
- means for outputting the modified speech signal.
13 more elements
Dependencies are inferred from the claim text.