Adaptive Linear Predictive Coding/Decoding

• US 20130103408A1
• Filed: 06/17/2011
• Published: 04/25/2013
• Est. Priority Date: 06/29/2010
• Status: Active Grant

• Current Assignee: Orange S.A.
• Original Assignee: Orange S.A.
• Inventors: Philippe, Pierrick, Virette, David, Lamblin, Claude
• Granted Patent: US 9,620,139 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
• CPC Class Codes: G10L 19/18 Vocoders using multiple modes
• CPC Class Codes: G10L 21/00 Speech or voice signal processing techniques to produce another audible or non-audible signal, e.g. visual or tactile, in order to modify its quality or its intelligibility G10L19/00 takes precedence

Abstract

A method of coding/decoding of a digital audio signal comprising a succession of consecutive blocks of data, on the basis of a predictive filter. A modified predictive filter is used for the coding of at least one current block, the modified filter being constructed by the combination of: a rear filter calculated for a past block, preceding the current block, and enrichment parameters for the rear filter, which are determined as a function of the signal in the current block and comprising the coefficients of a modifying filter.

Claims

1. A method of coding a digital audio signal comprising a succession of consecutive blocks of data, on the basis of a predictive filter, the method comprising the use of a modified predictive filter, for coding at least one current block, said modified filter being constructed by the combination of:

a backward filter calculated for a past block, preceding the current block, and

enrichment parameters of the backward filter determined as a function of the signal in the current block and comprising the coefficients of a modifying filter.

2. The method of claim 1, comprising, for coding a current block, a choice based on at least one predetermined criterion of a predictive filter from among at least:

a backward filter, calculated for a past block, preceding the current block, and

a forward filter, suitable for the current block, and

a modified filter, estimated on the basis of a backward filter and as a function of the signal in the current block.

3. The method of claim 2, wherein said criterion takes into account a stationarity of the signal between the past block and the current block, for the choice of one of the filters from among a backward filter, a forward filter and a modified filter.

4. The method of claim 3, wherein the predetermined criterion comprises an estimate of a prediction gain based on a relationship between the power of the signal in the current block and the power of a residual signal after this signal is filtered using each of said backward, forward and modified filters.

5. The method of claim 3, wherein said criterion further takes into account a number of parameters to be sent to a decoder for decoding a current block and comprising at least the coefficients that the filter to be chosen comprises.

6. The method of claim 5, wherein the predetermined criterion comprises a search for the optimum between:

the prediction gain offered by the filter, and

a bitrate suitable for transmitting said parameters.

7. The method of claim 1, comprising the steps of:

a) determining a plurality of forward filters of distinct respective orders,

b) determining a plurality of backward filters of distinct respective orders,

c) calculating a plurality of modified filters of distinct respective orders, each estimated on the basis of a backward filter determined in step b) and as a function of the signal in a current block,

d) comparing, for the same number of parameters to be sent to a decoder, this number being determined as a function of said filter orders, the performance of at least two filters from among said forward filters, said backward filters and said modified filters, and

e) selecting, for coding a current block, a predictive filter with the best performance according to the comparison of step d), for a given number of parameters to be sent to a decoder.

8. The method of claim 1, wherein the modifying filter is estimated by deconvolution of a forward filter suitable for filtering the current block, by said backward filter calculated for a past block.

9. The method of claim 1, wherein the modifying filter is determined on the basis of an analysis of a residual signal obtained after filtering of the current block by said backward filter calculated for a past block.

10. The method of claim 1, wherein the modifying filter is estimated by identification in the least squares sense, by calculating autocorrelation terms of the backward filter coefficients and intercorrelation between the modified filter and the backward filter.

11. The method of claim 1, further comprising an information message to a decoder, of the type:

choice of a forward filter for a current block, with a transmission of parameters representing coefficients of the forward filter,

or choice of a backward filter or a modified filter for a current block, with, in the case of a choice of a modified filter, a transmission of parameters representing coefficients of said modifying filter.

14. A signal encoding device for implementing the method of claim 1, comprising at least:

suitable means of calculating a modified filter on the basis of a backward filter and at least as a function of the signal in the current block, and

means of coding at least one current block using said modified filter.

16. A computer program comprising instructions for implementing the method of coding of claim 1, when this program is executed by a processor.

18. The method of claim 5, wherein the predetermined criterion comprises an estimate of a prediction gain based on a relationship between the power of the signal in the current block and the power of the residual signal after this signal is filtered using each of said backward, forward and modified filters.

12. A method of decoding a digital audio signal comprising a succession of consecutive blocks of data, the method using a predictive filter for decoding a current block, the method comprising:

a reception of information for calculating a modified predictive filter (A) based on the combination of;

a backward filter, calculated for a past block, preceding the current block, and

enrichment parameters of the backward filter, originating from the information received, comprising filter coefficients, for forming a modifying filter comprising said coefficients,

and use of said predictive filter thus modified for decoding at least one current block.

13. The method of claim 12, comprising the following steps for determining the backward filter:

determining an order of the backward filter, as a function of said received information, and

calculating the backward filter from previously decoded data and by using said filter order.

15. The signal decoding device for implementing the method of claim 12, comprising at least:

means of reception of information for calculating a modified predictive filter

suitable means of calculating said modified filter, based on;

a backward filter, calculated for a past block, preceding the current block, and

enrichment parameters of the backward filter, originating from the information received,

and means of decoding at least one current block using the modified filter.

17. A computer program comprising instructions for implementing the method of decoding of claim 12, when this program is executed by a processor.