Complex-valued synthesis filter bank with phase shift

• US 9,634,647 B2
• Filed: 11/30/2016
• Issued: 04/25/2017
• 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
• Primary Examiner(s): Yaary, Michael D
• Application Number:
  US15/364,384
• Publication Number:
  US 20170085250A1
• Time in Patent Office: 146 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

An apparatus for generating real-valued output audio samples is disclosed. The apparatus includes a memory that stores complex-valued input subband samples, real-valued demodulated samples, and the real-valued output audio samples. The apparatus also incudes a phase shifter that shifts a phase of the complex-valued input subband samples by an amount equal to a previously added phase shift and a complex-valued synthesis filter bank that generates the real-valued output audio samples in response to the complex-valued input subband samples, the real-valued demodulated samples, and prototype filter coefficients.

Claims

1. An apparatus for generating real-valued output audio samples, the apparatus comprising:

memory that stores complex-valued input subband samples, real-valued demodulated samples, and the real-valued output audio samples;

a phase shifter that shifts a phase of the complex-valued input subband samples by an amount equal to a previously added phase shift; and

a complex-valued synthesis filter bank that generates the real-valued output audio samples in response to the complex-valued input subband samples, the real-valued demodulated samples, and prototype filter coefficients, wherein the complex-valued synthesis filter bank;

shifts a first subset of the real-valued demodulated samples in the memory;

multiplies the complex-valued input subband samples by a complex-valued exponential modulation matrix to generate complex-valued demodulated samples;

stores the real part of the complex-valued demodulated samples in the memory as a second subset of the real-valued demodulated samples;

extracts a third subset of the real-valued demodulated samples from the memory;

multiplies the third subset of the real-valued demodulated samples by the prototype filter coefficients to generate windowed samples;

combines the windowed samples to generate the real-valued output audio samples; and

stores the real-valued output audio samples in the memory.

2. The apparatus of claim 1 wherein the prototype filter coefficients represent an asymmetric low-pass prototype filter or a symmetric low-pass prototype filter.

3. The apparatus of claim 1 wherein the real-valued demodulated samples are shifted by 128 positions in the memory.

4. The apparatus of claim 1 wherein the third subset of the real-valued demodulated samples comprises an array of 640 elements.

5. The apparatus of claim 1 wherein the complex-valued synthesis filter bank is a QMF filter bank.

6. The apparatus of claim 1 wherein the real-valued output audio samples are time domain audio samples.

7. The apparatus of claim 1 wherein the complex-valued synthesis filter bank is part of a high frequency reconstruction (HFR) module that reconstructs high frequency components of the audio signal.

8. The apparatus of claim 1 wherein the memory comprises a collective memory of an audio decoder.

9. The apparatus of claim 1 wherein the real-valued output audio samples comprise an array of 64 samples.

10. A method for generating real-valued output audio samples, the method comprising:

storing complex-valued input subband samples in a memory;

shifting a phase of the complex-valued input subband samples by an amount equal to a previously added phase shift;

generating the real-valued output audio samples in response to the complex-valued input subband samples, real-valued demodulated samples, and prototype filter coefficients using a complex-valued synthesis filter bank; and

storing the real-valued output audio samples in the memory,

wherein the complex-valued synthesis filter bank;

shifts a first subset of the real-valued demodulated samples in the memory;

multiplies the complex-valued input subband samples by a complex-valued exponential modulation matrix to generate complex-valued demodulated samples;

stores the real part of the complex-valued demodulated samples in the memory as a second subset of the real-valued demodulated samples;

extracts a third subset of the real-valued demodulated samples from the memory;

multiplies the third subset of the real-valued demodulated samples by the prototype filter coefficients to generate windowed samples;

combines the windowed samples to generate the real-valued output audio samples; and

stores the real-valued output audio samples in the memory.

11. The method of claim 10 wherein the prototype filter coefficients represent an asymmetric low-pass prototype filter or a symmetric low-pass prototype filter.

12. The method of claim 10 wherein the real-valued demodulated samples are shifted by 128 positions in the memory.

13. The method of claim 10 wherein the third subset of the real-valued demodulated samples comprises an array of 640 elements.

14. The apparatus of claim 10 wherein the real-valued output audio samples are time domain audio samples.

15. The method of claim 10 wherein the complex-valued low delay synthesis filter bank is used as part of a high frequency reconstruction (HFR) process for reconstructing high frequency components of the audio signal.

16. The method of claim 10 wherein the complex-valued low delay synthesis filter bank is a QMF filter bank.

17. The apparatus of claim 10 wherein the real-valued output audio samples comprise an array of 64 samples.

18. The apparatus of claim 10 wherein the memory comprises a collective memory of an audio decoder.