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EP0481374A2
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Dynamic bit allocation subband excited transform coding method and apparatus
Assignee: Verizon Laboratories Inc
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Filing: 1991-10-11
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Granted: —
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Expires: 2011-10-11
Abstract
Abstract In an adaptive subband excited transform speech encoding system, a range of quantizers (30) are available and are dynamically selected for each window of speech. The quantizers (30) designated for individual subbands are determined to minimize mean squared error distortion in the recreated signal while using no more than a predetermined number of quantization bits per window of speech.
Inventors
- 👤 Baruch Mazor
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-02 05:24
CPC Classifications
H; H04; H04B; H04B1/00; H04B1/66; H04B1/667; G; G10; G10L; G10L19/00; G10L19/02; G10L19/0204
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
127 words
A speech coding system comprising: transform means for performing a discrete transform of a window of speech to generate a discrete transform spectrum of coefficients; envelope defining and encoding means for defining an approximate envelope of the discrete spectrum in each of a plurality of subbands of coefficients and for encoding the defined envelope of each subband of coefficients; means for scaling each spectrum coefficient relative to the defined envelope of the respective subband of coefficients; a plurality of quantizers of different bit lengths for encoding scaled spectrum coefficients within each subband; and means for determining a quantizer, if any, to be used to encode the coefficients of each subband within each window of speech wherein the selection of available quantizers used in successive windows is variable.
Claim 2
Dependent Claim
25 words
A speech coding system as claimed in Claim 1 wherein the means for determining allocates bits to minimize quantization error for each window of speech.
Claim 3
Dependent Claim
38 words
A speech coding system as claimed in Claim 1 wherein the means for determining iteratively estimates distortion and computes for each distortion estimate a bit allocation across the spectrum to near fully allocate a predetermined number of bits.
Claim 4
Dependent Claim
63 words
A speech coding system as claimed in Claim 3 wherein the means for determining computes the allocation of bits as a number of bits greater than or equal to zero which is derived from log₂(P i /D) for each subband where P i is a power density estimate for the subband and D is a distortion error estimate for the window of speech.
Claim 5
Dependent Claim
27 words
A speech coding system as claimed in Claim 4 wherein P i is estimated for each subband from the defined envelope of the respective subband of coefficients.
Claim 6
Dependent Claim
39 words
A speech coding system as claimed in Claim 4 wherein the means for determining tunes the computed bit allocation toward the number of available bits by adding bits to higher energy subbands or subtracting bits from lower energy subbands.
Claim 7
Dependent Claim
27 words
A speech coding system as claimed in Claim 6 wherein P i is estimated for each subband from the defined envelope of the respective subband of coefficients.
Claim 8
Dependent Claim
18 words
A speech coding system as claimed in Claim 1 wherein the transform means performs a discrete Fourier transform.
Claim 9
Independent Claim
92 words
A method of coding speech comprising: performing a discrete transform of a window of speech to generate a discrete spectrum of coefficients; defining an approximate envelope of the discrete spectrum in each of a plurality of subbands of coefficients and digitally encoding the defined envelope of each subband of coefficients; and with at least one of a plurality of quantizers of different bit lengths, encoding each of scaled coefficients within subbands into a number of bits, the quantizer used for each subband being determined for each window of speech to minimize distortion.
Claim 10
Dependent Claim
21 words
A method as claimed in Claim 9 wherein the quantizers are determined to minimize quantization error for each window of speech.
Claim 11
Dependent Claim
37 words
A method as claimed in Claim 9 wherein the quantizers are determined by iteratively estimating distortion and computing for each distortion estimate a bit allocation across the spectrum to nearly fully allocate a predetermined number of bits.
Claim 12
Dependent Claim
63 words
A method as claimed in Claim 11 wherein the quantizers are determined by computing the allocation of bits as a number of bits greater than or equal to zero which is derived from log₂ (P i /D) for each subband where P i is a power density estimate for the subband and D is a distortion error estimate for the window of speech.
Claim 13
Dependent Claim
25 words
A method as claimed in Claim 12 wherein P i is estimated for each subband from the defined envelope of the respective subband of coefficients.
Claim 14
Dependent Claim
34 words
A method as claimed in claim 12 wherein the allocation of bits is tuned toward the number of available bits by adding bits to higher energy subbands and subtracting bits from lower energy subbands.
Claim 15
Dependent Claim
25 words
A method as claimed in Claim 6 wherein P i is estimated for each subband from the defined envelope of the respective subband of coefficients.
Claim 16
Dependent Claim
15 words
A method as claimed in Claim 1 wherein the transform is a discrete Fourier transform.
References Cited (Backward Citations)
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