Complex-valued synthesis filter bank with phase shift

Patent metadata

Field	Value
Publication number	US-9634647-B2
Application number	US-201615364384-A
Country	US
Kind code	B2
Filing date	Nov 30, 2016
Priority date	Feb 18, 2009
Publication date	Apr 25, 2017
Grant date	Apr 25, 2017

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.

First claim

The invention claimed is:

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.

Assignees

• Dolby Int Ab

Inventors

• Ekstrand Per

Classifications

• G10L19/26

  Pre-filtering or post-filtering · CPC title

• G10L21/00 Primary

  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 title

• H04S7/307

  Frequency adjustment, e.g. tone control (H04S7/301 takes precedence) · CPC title

• H03H17/0266 Primary

  Filter banks · CPC title

• H03H17/0248

  Filters characterised by a particular frequency response or filtering method · CPC title