Low delay modulated filter bank

• US 9,865,275 B2
• Filed: 07/20/2016
• Issued: 01/09/2018
• Est. Priority Date: 02/18/2009
• Status: Active Grant

• Current Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Original Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Inventors: Ekstrand, Per, Appleton, Nicholas Luke
• Primary Examiner(s): Yaary, Michael D
• Application Number:
  US15/214,694
• Publication Number:
  US 20160329062A1
• Time in Patent Office: 538 Days
• Field of Search: None
• CPC Class Codes: G06F 17/10 Complex mathematical operations function generation by table look-up G06F1/03; evaluation of elementary functions by calculation G06F7/544
• CPC Class Codes: G06F 17/11 for solving equations , e.g. nonlinear equations, general mathematical optimization problems optimization specially adapted for a specific administrative, business or logistic context G06Q10/04
• CPC Class Codes: G10L 19/008 Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/0208 Subband vocoders
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 19/265 Pre-filtering, e.g. high frequency emphasis prior to encoding
• 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
• CPC Class Codes: H03H 17/0201 Wave digital filters
• CPC Class Codes: H03H 17/0248 Filters characterised by a particular frequency response or filtering method
• CPC Class Codes: H03H 17/0266 Filter banks
• CPC Class Codes: H03H 17/0275 comprising non-recursive filters
• CPC Class Codes: H03H 17/0294 Variable filters; Programmable filters
• CPC Class Codes: H03H 2017/0297 Coefficients derived from input parameters
• CPC Class Codes: H04R 3/04 for correcting frequency response
• CPC Class Codes: H04S 7/307 Frequency adjustment, e.g. tone control H04S7/301 takes precedence

Abstract

The document relates to modulated digital filter banks, as well as to methods and systems for the design of such filter banks. In particular, the document discloses a method comprising accessing a time-domain audio signal and applying a first filter bank to the time-domain audio signal, thereby producing a first plurality of subbands of frequency-domain audio data representative of at least a part of the audio signal. The filter bank comprises an decimated modulated filter bank obtained from an asymmetric prototype filter. The method further comprises applying a second filter bank to at least a first subband of the first plurality of subbands of frequency-domain audio data, thereby producing a second plurality of subbands of frequency-domain audio data representative of at least a part of the audio signal. The second modulated filter bank comprises an asymmetric modulated filter bank which includes no decimation. The method further comprises outputting at least the second plurality of subbands of frequency domain audio data.

Claims

1. An apparatus comprising:

an interface configured to receive time-domain audio signals and to output frequency-domain audio data; and

a logic system in communication with the interface, the logic system being configured to;

apply a first filter bank to a time-domain audio signal, thereby producing a first plurality of subbands of frequency-domain audio data representative of at least a part of the audio signal, wherein the filter bank comprises an decimated modulated filter bank obtained from an asymmetric prototype filter;

apply a second filter bank to at least a first subband of the first plurality of subbands of frequency-domain audio data, thereby producing a second plurality of subbands of frequency-domain audio data representative of at least a part of the audio signal, wherein the second modulated filter bank comprises an asymmetric modulated filter bank which includes no decimation; and

output, via the interface, at least the second plurality of subbands of frequency domain audio data.

2. The apparatus of claim 1 wherein the asymmetric modulated filter bank which includes no decimation is a Nyquist filter bank.

3. The apparatus of claim 2 wherein the Nyquist filter bank is obtained using a Nyquist prototype filter of length eleven.

4. The apparatus of claim 2 wherein the Nyquist filter bank is obtained using a Nyquist prototype filter with a delay of three samples.

5. The apparatus of claim 1 wherein said first subband is the lowest-frequency subband of the first plurality of subbands of frequency-domain audio data.

6. The apparatus of claim 1 wherein the logic system is configured to apply the second filter bank to only said first subband, and wherein the second plurality of subbands of frequency-domain audio data consists of eight subbands of frequency-domain audio data.

7. The apparatus of claim 1 wherein the logic system is further configured to:

apply a third filter bank to at least a second subband of the first plurality of subbands of frequency-domain audio data, thereby producing a third plurality of subbands of frequency-domain audio data representative of a part of the audio signal, wherein the third modulated filter bank comprises an asymmetric modulated filter bank which includes no decimation

output, via the interface, the third plurality of subbands of frequency domain audio data.

8. The apparatus of claim 1 wherein the asymmetric modulated filter bank which includes no decimation is a Nyquist filter bank.

9. The apparatus of claim 8 wherein the Nyquist filter bank is obtained using a Nyquist prototype filter of length eleven.

10. The apparatus of claim 8 wherein the Nyquist filter bank is obtained using a Nyquist prototype filter with a delay of three samples.

11. The apparatus of claim 7 wherein said second subband is the second-lowest-frequency subband of the first plurality of subbands of frequency-domain audio data.

12. The apparatus of claim 7 wherein the logic system is configured to apply the third filter bank to only said second subband, and wherein the third plurality of subbands of frequency-domain audio data consists of four subbands of frequency-domain audio data.

13. The apparatus of claim 1 wherein the logic system is further configured to:

apply a fourth filter bank to at least a third subband of the first plurality of subbands of frequency-domain audio data, thereby producing a fourth plurality of subbands of frequency-domain audio data representative of a part of the audio signal, wherein the fourth modulated filter bank comprises an asymmetric modulated filter bank which includes no decimation output, via the interface, the fourth plurality of subbands of frequency domain audio data.

14. The apparatus of claim 13 wherein the asymmetric modulated filter bank which includes no decimation is a Nyquist filter bank.

15. The apparatus of claim 14 wherein the Nyquist filter bank is obtained using a Nyquist prototype filter of length eleven.

16. The apparatus of claim 14 wherein the Nyquist filter bank is obtained using a Nyquist prototype filter with a delay of three samples.

17. The apparatus of claim 13 wherein said third subband is the third-lowest-frequency subband of the first plurality of subbands of frequency-domain audio data.

18. The apparatus of claim 13 wherein the logic system is configured to apply the fourth filter bank to only said third subband, and wherein the fourth plurality of subbands of frequency-domain audio data consists of four subbands of frequency-domain audio data.

19. A method comprising:

accessing a time-domain audio signal;

applying a first filter bank to the time-domain audio signal, thereby producing a first plurality of subbands of frequency-domain audio data representative of at least a part of the audio signal, wherein the filter bank comprises an decimated modulated filter bank obtained from an asymmetric prototype filter;

applying a second filter bank to at least a first subband of the first plurality of subbands of frequency-domain audio data, thereby producing a second plurality of subbands of frequency-domain audio data representative of at least a part of the audio signal, wherein the second modulated filter bank comprises an asymmetric modulated filter bank which includes no decimation; and

outputting at least the second plurality of subbands of frequency domain audio data.

20. A non-transitory, computer-readable storage medium on which is stored a computer program which, when executed by a logic system of an apparatus which comprises the logic system and, in communication therewith, an interface configured to receive time-domain audio signals and to output frequency-domain audio data, configured the logic system to:

apply a first filter bank to a time-domain audio signal, thereby producing a first plurality of subbands of frequency-domain audio data representative of at least a part of the audio signal, wherein the filter bank comprises an decimated modulated filter bank obtained from an asymmetric prototype filter;

apply a second filter bank to at least a first subband of the first plurality of subbands of frequency-domain audio data, thereby producing a second plurality of subbands of frequency-domain audio data representative of at least a part of the audio signal, wherein the second modulated filter bank comprises an asymmetric modulated filter bank which includes no decimation; and

output, via the interface, at least the second plurality of subbands of frequency domain audio data.