FILTER COEFFICIENT UPDATING IN TIME DOMAIN FILTERING

• US 20180254053A1
• Filed: 09/15/2016
• Published: 09/06/2018
• Est. Priority Date: 09/18/2015
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: SHI, Dong, SUN, Xuejing
• Granted Patent: US 10,332,540 B2
• Time in Patent Office: Days
• CPC Class Codes: G10L 25/18 the extracted parameters being spectral information of each sub-band
• CPC Class Codes: G10L 25/48 specially adapted for particular use
• CPC Class Codes: H03H 17/0227 Measures concerning the coefficients
• CPC Class Codes: H03H 17/0294 Variable filters; Programmable filters
• CPC Class Codes: H03H 21/0025 Particular filtering methods
• CPC Class Codes: H03H 21/0043 Adaptive algorithms

Abstract

Example embodiments disclosed herein relate to filter coefficient updating in time domain filtering. A method of processing an audio signal is disclosed. The method includes obtaining a predetermined number of target gains for a first portion of the audio signal by analyzing the first portion of the audio signal. Each of the target gains is corresponding to a linear subband of the audio signal. The method also includes determining a filter coefficients for time domain filtering the first portion of the audio signal so as to approximate a frequency response given by the target gains. The filter coefficients are determined by iteratively selecting at least one target gain from the target gains and updating the filter coefficient based on the selected at least one target gain. Corresponding system and computer program product for processing an audio signal are also disclosed.

Claims

1. A method of processing an audio signal comprising:

obtaining a predetermined number of target gains for a first portion of the audio signal by analyzing the first portion of the audio signal, each of the target gains corresponding to a subband of the audio signal; and

determining filter coefficients for filtering the first portion of the audio signal so as to approximate a frequency response given by the obtained target gains, the filter coefficients determined by iteratively

selecting at least one target gain from the target gains, and

updating the filter coefficients based on the filter coefficients of the previous iteration and the selected at least one target gain, and

filtering the first portion of the audio signal in time domain based on the filter coefficients.

2. The method of claim 1, wherein obtaining the target gains comprises:

determining the predetermined number based on an order of the filtering.

3. The method of claim 1 or 2, wherein selecting at least one target gain from the target gains comprises:

selecting at least one target gain from the target gains based on at least one of the following;

computation resources available for the updating of the filter coefficient, or

a convergence requirement of the updating of the filter coefficient.

4. The method of any of claims 1 to 3, wherein selecting at least one target gain from the target gains comprises:

for a first target gain from the target gains for the first portion, determining a difference between the first target gain and a second target gain for a second portion of the audio signal, the second portion being prior to the first portion, the first and second target gains being corresponding to a same linear subband; and

selecting the first target gain in response to the difference exceeding a predetermined threshold.

5. The method of any of claims 1 to 4, wherein updating the filter coefficient based on the selected at least one target gain comprises:

obtaining a mapping that correlates the selected at least one target gain to the filter coefficient; and

updating the filter coefficient based on the selected at least one target gain and the mapping.

6. The method of any of claims 1 to 5, wherein updating the filter coefficient based on the selected at least one target gain comprises:

for a first target gain from the selected at least one target gain for the first portion, smoothing the first target gain based on a smoothing factor and a second target gain for a second portion of the audio signal, the second portion being prior to the first portion, the first and second target gains being corresponding to a same linear subband; and

updating the filter coefficient based on the smoothed target gain.

7. The method of any of claims 1 to 6, wherein the predetermined number is a first predetermined number and the subbands are linear subbands, the method further comprising:

converting the first predetermined number of target gains into a second predetermined number of target gains, each of the second predetermined number of target gains corresponding to a perceptual subband of the audio signal, the second predetermined number being lower than the first predetermined number, and

wherein selecting at least one target gain from the target gains comprises;

selecting at least one target gain from the second predetermined number of target gains.

8. The method of any of claims 1 to 7, wherein the filter coefficients are determined based on a least square method.

9. The method of any of claims 1 to 8, wherein the filter coefficients are updated based on the selected at least one target gain and a predetermined mapping matrix.

10. The method of claim 9, wherein the updating comprises selecting a mapping column from the mapping matrix based on the selected at least one target gain.

11. The method of any previous claim, wherein the filter coefficients are updated based on a linear combination of the selected target gains and respective mapping columns from the mapping matrix.

23. A computer program product for processing an audio signal, comprising a computer program tangibly embodied on a machine readable medium, the computer program containing program code for performing the method according to any one of claims 1 to 11.

12. A system for processing an audio signal, comprising:

a target gain obtaining module configured to obtain a predetermined number of target gains for a first portion of the audio signal by analyzing the first portion of the audio signal, each of the target gains corresponding to a subband of the audio signal; and

a coefficient determination module configured to determine filter coefficients for filtering the first portion of the audio signal so as to approximate a frequency response given by the obtained target gains, the filter coefficients determined by iteratively;

selecting at least one target gain from the target gains, and

updating the filter coefficients based on the filter coefficients of the previous iteration and the selected at least one target gain, and

an audio filtering module configured to filter the first portion of the audio signal in time domain based on the updated filter coefficients.

13. The system of claim 12, wherein the target gain obtaining module is further configured to determine the predetermined number based on an order of the filtering.

14. The system of claim 12 or 13, wherein the coefficient determination module is further configured to select at least one target gain from the target gains based on at least one of the following:

computation resources available for the updating of the filter coefficient, or

a convergence requirement of the updating of the filter coefficient.

15. The system of any of claims 12 to 14, wherein the coefficient determination module is further configured to:

for a first target gain from the target gains for the first portion, determine a difference between the first target gain and a second target gain for a second portion of the audio signal, the second portion being prior to the first portion, the first and second target gains being corresponding to a same linear subband; and

select the first target gain in response to the difference exceeding a predetermined threshold.

16. The system of any of claims 12 to 15, wherein the coefficient determination module is further configured to:

obtain a mapping that correlates the selected at least one target gain to the filter coefficient; and

update the filter coefficient based on the selected at least one target gain and the mapping.

17. The system of any of claims 12 to 15, wherein the coefficient determination module is further configured to:

for a first target gain from the selected at least one target gain for the first portion, smooth the first target gain based on a smoothing factor and a second target gain for a second portion of the audio signal, the second portion being prior to the first portion, the first and second target gains being corresponding to a same linear subband; and

update the filter coefficient based on the smoothed target gain.

18. The system of any of claims 12 to 16, wherein the predetermined number is a first predetermined number and the subbands are linear subbands, the system further comprising:

a target gain converting module configured to convert the first predetermined number of target gains into a second predetermined number of target gains, each of the second predetermined number of target gains corresponding to a perceptual subband of the audio signal, the second predetermined number being lower than the first predetermined number, and

wherein the coefficient determination module is further configured to select at least one target gain from the second predetermined number of target gains.

19. The system of any of claims 12 to 18, wherein the filter coefficients are determined based on a least square method.

20. The system of any of claims 12 to 19, wherein the filter coefficients are updated based on the selected at least one target gain and a predetermined mapping matrix.

21. The system of claim 20, wherein the updating comprises selecting a mapping column from the mapping matrix corresponding to the selected at least one target gain.

22. The system of any of claims 12 to 21, wherein the filter coefficients are updated based on a linear combination of the selected target gains and respective mapping columns in the mapping matrix.