US4625286A
Expired / Lapsed
US
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Time encoding of LPC roots
Assignee: Texas Instruments Inc
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Filing: 1982-05-03
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Granted: 1986-11-25
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Expires: 2002-05-03
Abstract
Abstract Since the formants in human speech move slowly over time, their slow time-varying behavior provides a source of information redundancy which can be used to reduce the required data rate in encoding of speech. In the present invention, speech is encoded by an adaptive tracking procedure, which follows the time-varying behavior of the speech parameters (e.g. the roots of the LPC inverse filter) with a minimum bit rate. A sequence of frames of parameters is segmented into locally-smooth segments which are approximated by higher-order orthogonal functions, and the required best-fit approximation order and coefficients are encoded.
Inventors
- 👤 Panos E. Papamichalis
- 👤 George R. Doddington
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 18:03
CPC Classifications
G; G10; G10L; G10L19/00; G10L19/04; G10L19/06
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
154 words
A method for LPC encoding of speech, comprising the steps of: providing, at each of a plurality of repeated frame intervals, a set of speech parameters; grouping said frame intervals into segments, such that each of said speech parameters varies smoothly from frame to frame within each of said segments; successively approximating values of each respective one of said parameters within each said respective segment, with linear combinations of orthogonal functions of successively higher order, until a final one of said linear combinations provides a predetermined degree of approximation to said respective parameter within said respective segment; and encoding, for each said respective segment, the number of frames within said segment, and, for each respective parameter within said respective segment, the order of said orthogonal functions in said final linear combination which provides said predetermined degree of approximation, and the respective coefficients of each of said orthogonal functions in said respective final linear combination.
Claim 2
Independent Claim
154 words
A method for LPC encoding of speech, comprising the steps of: providing, at each of a plurality of repeated frame intervals, a set of speech parameters; grouping said frame intervals into segments, such that each of said speech parameters varies smoothly from frame to frame within each of said segments; successively approximating values of each respective one of said parameters within each said respective segment, with linear combinations of orthogonal functions of successively higher order, until a final one of said linear combinations provides a predetermined degree of approximation to said respective parameter within said respective segment; and encoding, for each said respective segment, the number of frames within said segment, and, for each respective parameter within said respective segment, the order of said orthogonal functions in said final linear combination which provides said predetermined degree of approximation, and the respective coefficients of each of said orthogonal functions in said respective final linear combination.
Claim 3
Dependent Claim
11 words
The method of claim 1, wherein said orthogonal functions comprise polynomials.
Claim 4
Dependent Claim
12 words
The method of claim 2, wherein said orthogonal functions comprise Legendre polynomials.
Claim 5
Dependent Claim
56 words
The method of claim 2, wherein said family of orthongonal functions P n (x) is defined, in accordance with the number N of said frmes in said respective segment, by the recursive relation: ##EQU7## where x n are equally speced real numbers designating successive ones of said frames within said segment, and P 0 (x) =1.
Claim 6
Dependent Claim
26 words
The method of claim 1, further comprising the step of: identifying corresponding ones of said parameters within adjacent ones of said frames within said respective segment.
Claim 7
Dependent Claim
19 words
The method of claim 5, wherein said speech parameters comprise poles of the linear predictive coding filter transfer function.
Claim 8
Dependent Claim
91 words
The method of claim 5, further comprising the step of: identifying excluded values of respective ones of said speech parameters within each of said frames within said segment; lumping said excluded values together, to form a residual polynomial for each segment; transforming each said respective residual polynomial to provide corresponding reflection coefficients; and identifying corresponding ones of said reflection coefficients of said residual polynomial over all of said frames; prior to said step of successively approximating; whereby said reflection coefficients of said residual polynomial are approximated as only two parameter tracks.
Claim 9
Dependent Claim
19 words
The method of claim 1, wherein said grouping step comprises defining a segment end point at each voiced/unvoiced transition.
Claim 10
Dependent Claim
29 words
The method of claim 1, wherein said grouping step comprises defining a segment end point wherever a local maxmum of a dissimilarity measure above a predetermined threshold is attained.
Claim 11
Dependent Claim
43 words
The method of claim 9, wherein said dissimilarity measure comprises the sum of the Itakura likelihood ratio of a given frame with respect to its following frame, together with the Itakura ratio of the following frame with respect to its respective preceding frame.
Claim 12
Dependent Claim
72 words
The method of claim 1, wherein similar values of respective ones of said parameters are linked between successive frames, such that no parameter value is linked to more than one parameter value in a preceding or following frame, so that the concatenation of linked parameter values so defined defines a parameter track; and wherein said grouping step comprises defining a segment end point wherever one of said parameter tracks begins or ends.
Claim 13
Dependent Claim
12 words
The method of claim 1, wherein said speech parameters comprise reflection coefficients.
Claim 14
Dependent Claim
33 words
The method of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, wherein said encoding step comprises the step of encoding said respective values in a read-only memory.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1989-11-24 | 1990-05-26 | 1990-11-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-11-24 | 1994-05-26 | 1994-11-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-11-24 | 1998-05-26 | 1998-11-25 | $7700.00 | Window Closed / Lapsed |