Effective deployment of Temporal Noise Shaping (TNS) filters
View Patent ↗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.
1. An audio encoding or audio decoding method for encoding or decoding an audio signal, the method comprising:
calculating, by a system including a processor, filters for a plurality of frequency bands, the filters comprising coefficients;
determining, by the system, distances between the coefficients;
merging, by the system, the filters based on the distances to yield merged filters;
and processing, by the system, the audio signal using centroids of subsets of the merged filters,
wherein one or more of the calculating, the determining, and the merging is implemented, at least in part, by one or more hardware elements of an audio signal processing device.
2. The audio encoding or audio decoding method of claim 1 , wherein the merging of the filters is based on energies in each of the plurality of frequency bands covered by the filters.
3. The audio encoding or audio decoding method of claim 1 , wherein the filters are temporal noise shaping filters.
4. The audio encoding or audio decoding method of claim 1 , wherein the coefficients are partial autocorrelation coefficients.
5. The audio encoding or audio decoding method of claim 1 , wherein the merging of the filters comprises calculating a new filter for a frequency range comprising adjacent frequency bands of the filters with a shortest distance.
6. The audio encoding or audio decoding method of claim 1 , wherein the merging of the filters comprises calculating a temporal noise filter for a frequency range comprising adjacent frequency bands of the filters.
7. The audio encoding or audio decoding method of claim 1 , wherein the processing of the audio signals comprises recalculating the merged filters for a strongest audio signal in a temporal noise shape band.
8. The audio encoding or audio decoding method of claim 1 , wherein the merging of the filters based on the distances is according to shortest distances.
9. An audio encoder or audio decoder system for encoding or decoding an audio signal, the system comprising:
a processor; and
a memory that stores executable instructions that, when executed by the processor, facilitate performance of operations, comprising:
calculating filters for a plurality of frequency bands, the filters comprising coefficients;
determining distances between the coefficients;
merging the filters based on the distances to yield merged filters;
and processing the audio signal using centroids of subsets of the merged filters,
wherein one or more of the processor, the memory, the filters, and the merged is implemented, at least in part, by one or more hardware elements of the audio encoder or audio decoder system.
10. The system of claim 9 , wherein the merging of the filters is based on energies in each of the plurality of frequency bands covered by the filters.
11. The system of claim 9 , wherein the coefficients are partial autocorrelation coefficients.
12. The system of claim 9 , wherein the merging of the filters comprises calculating a new filter for a frequency range comprising adjacent frequency bands of the filters with a shortest distance.
13. The system of claim 9 , wherein the processing of the audio signals comprises recalculating the merged filters for a strongest audio signal in a temporal noise shape band.
14. The system of claim 9 , wherein the merging of the filters based on the distances is according to shortest distances.
15. The system of claim 9 , wherein the filters are temporal noise shaping filters.
16. A non-transitory and machine-readable storage medium, comprising executable instructions that, when executed by a processor, facilitate performance of an audio encoding or audio decoding method for encoding or decoding an audio signal, the method comprising:
calculating filters for a plurality of frequency bands, the filters comprising coefficients;
determining distances between the coefficients;
merging the filters based on the distances to yield merged filters; and
processing the audio signal using centroids of subsets of the merged filters.
17. The non-transitory and machine-readable storage medium of claim 16 , wherein the merging of the filters is based on energies in each of the plurality of frequency bands covered by the filters.
18. The non-transitory and machine-readable storage medium of claim 16 , wherein the coefficients are partial autocorrelation coefficients.
19. The non-transitory and machine-readable storage medium of claim 16 , wherein the merging of the filters comprises calculating a new filter for a frequency range comprising adjacent frequency bands of the filters with a shortest distance.
20. The non-transitory and machine-readable storage medium of claim 16 , wherein the processing of the audio signals comprises recalculating the merged filters for a strongest audio signal in a temporal noise shape band.