EFFECTIVE DEPLOYMENT OF TEMPORAL NOISE SHAPING (TNS) FILTERS

• US 20100100211A1
• Filed: 12/22/2009
• Published: 04/22/2010
• Est. Priority Date: 03/29/2000
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Johnston, James David, Kuo, Shyh-Shiaw
• Granted Patent: US 8,452,431 B2
• Time in Patent Office: Days
• US Class Current: 700/94
• CPC Class Codes: G10L 19/03 Spectral prediction for preventing pre-echo; Temporary noise shaping [TNS], e.g. in MPEG2 or MPEG4

Abstract

The MPEG2 Advanced Audio Coder (AAC) standard limits the number of filters used to either one filter for a “short” block or three filters for a “long” block. In cases where the need for additional filters is present but the limit of permissible filters has been reached, the remaining frequency spectra are simply not covered by TNS. Two solutions are proposed to deploy TNS filters in order to get the entire spectrum of the signal into TNS. The first method involves a filter bridging technique and complies with the current AAC standard. The second method involves a filter clustering technique. Although the second method is both more efficient and accurate in capturing the temporal structure of the time signal, it is not AAC standard compliant. Thus, a new syntax for packing filter information derived using the second method for transmission to a receiver is also outlined.

Claims

1. A method of using filters to process audio signals, the method causing a computing device to perform steps comprising:

calculating a filter for each of a plurality of frequency bands;

determining a distance between coefficients in adjacent frequency bands;

clustering the filters into at least two groups based on energies in each of the frequency bands covered by the filters;

merging the clustered filters with a shortest distance between coefficients; and

processing audio signals using the merged filters.

2. The method of claim 1, wherein the filters are temporal noise shaping (TNS) filters.

3. The method of claim 1, wherein the coefficients are partial autocorrelation (PARCOR) coefficients.

4. The method of claim 3, wherein clustering the filters in at least two groups further comprises:

clustering the temporal noise shaping filters based on respective PARCOR coefficients of the temporal noise shaping filters.

5. The method of claim 1, wherein merging clustered filters includes calculating a new filter for a frequency range comprising the adjacent frequency bands of the filters with the shortest distance.

6. The method of claim 1, wherein merging the clustered filters further comprises:

calculating a new temporal noise filter for a frequency range comprising adjacent frequency bands of the temporal noise shaping filters with the shortest distance.

7. A system for processing audio signals using filters, the system comprising:

a processor;

a module controlling the processor to calculate a filter for each of a plurality of frequency bands;

a module controlling the processor to determine a distance between coefficients in adjacent frequency bands;

a module controlling the processor to cluster the filters into at least two groups based on energies in each of the frequency bands covered by the filters;

a module controlling the processor to merge the clustered filters with a shortest distance between coefficients; and

a module controlling the processor to process audio signals using the merged filters.

8. The system of claim 7, wherein the filters are temporal noise shaping (TNS) filters.

9. The system of claim 7, wherein the coefficients are partial autocorrelation (PARCOR) coefficients.

10. The system of claim 9, wherein the module controlling the processor to cluster the filters in at least two groups further causes the processor to cluster the temporal noise shaping filters based on respective PARCOR coefficients of the temporal noise shaping filters.

11. The system of claim 7, wherein the module controlling the processor to merge clustered filters further causes the processor to calculate a new filter for a frequency range comprising the adjacent frequency bands of the filters with the shortest distance.

12. The system of claim 7, wherein the module controlling the processor to merge the clustered filters further causes the processor to calculate a new temporal noise filter for a frequency range comprising adjacent frequency bands of the temporal noise shaping filters with the shortest distance.

13. A computer-readable storage medium storing instructions which, when executed by a computing device, cause the computing device to use filters to process audio signals, the instructions comprising:

calculating a filter for each of a plurality of frequency bands;

determining a distance between coefficients in adjacent frequency bands;

clustering the filters into at least two groups based on energies in each of the frequency bands covered by the filters;

merging the clustered filters with a shortest distance between coefficients; and

processing audio signals using the merged filters.

14. The computer-readable storage medium of claim 13, wherein the filters are temporal noise shaping (TNS) filters.

15. The computer-readable storage medium of claim 13, wherein the coefficients are partial autocorrelation (PARCOR) coefficients.

16. The computer-readable storage medium of claim 15, wherein clustering the filters in at least two groups further comprises clustering the temporal noise shaping filters based on respective PARCOR coefficients of the temporal noise shaping filters.

17. The computer-readable storage medium of claim 13, wherein merging clustered filters includes calculating a new filter for a frequency range comprising the adjacent frequency bands of the filters with the shortest distance.

18. The computer-readable storage medium of claim 13, wherein merging the clustered filters further comprises calculating a new temporal noise filter for a frequency range comprising adjacent frequency bands of the temporal noise shaping filters with the shortest distance.