Complex exponential modulated filter bank for high frequency reconstruction or parametric stereo

• US 9,762,210 B1
• Filed: 05/30/2017
• Issued: 09/12/2017
• 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): Mai, Tan V.
• Application Number:
  US15/608,020
• Publication Number:
  US 20170264271A1
• Time in Patent Office: 105 Days
• 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 and method are disclosed for filtering an audio signal. The apparatus includes an analysis filter bank, a phase shifter, a high frequency reconstructor or parametric stereo processor, and a synthesis filter bank. The analysis filterbank receives real-valued time domain input audio samples and generates complex valued subband samples. The phase shifter shifts a phase of the complex-valued subband samples by an amount. The high frequency reconstructor or parametric stereo processor modifies at least some of the complex valued subband samples. A phase shifter then unshifts a phase of the modified complex-valued subband samples by the amount. The synthesis filter bank receives the modified complex valued subband samples and generates time domain output audio samples.

Claims

1. A signal processing device for filtering and processing an audio signal, the signal processing device comprising:

an analysis filter bank that receives real valued time domain input audio samples and generates complex-valued subband samples;

a phase shifter that shifts a phase of the complex-valued subband samples by an amount;

a high frequency reconstructor or a parametric stereo processor that generates modified complex-valued subband samples;

a phase shifter that unshifts a phase of the modified complex-valued subband samples by the amount; and

a synthesis filter bank that receives the modified complex-valued subband samples and generates time domain output audio samples,

wherein the analysis filter bank comprises analysis filters (h_k(n)) that are complex exponential modulated versions of a prototype filter (p₀(n)) according to;

2. The signal processing device of claim 1 wherein the prototype filter (p₀(n)) is a symmetric low pass prototype filter or an asymmetric low pass prototype filter.

3. The signal processing device of claim 1 wherein the analysis filter bank is a pseudo QMF bank.

4. The signal processing device of claim 1 wherein an order of the prototype filter (p₀(n)) equals the system delay D.

5. The signal processing device of claim 1 wherein the high frequency reconstructor performs spectral band replication (SBR).

6. The signal processing device of claim 1 wherein a value of the amount is chosen to reduce a complexity of an implementation of the apparatus.

7. The signal processing device of claim 1 wherein the one or more hardware elements comprise a digital signal processor, a microprocessor, or a memory.

8. The signal processing device of claim 1 wherein a number of channels in the analysis filter bank is different than a number of channels in the synthesis filter bank.

9. The signal processing device of claim 8 wherein the number of channels in the analysis filter bank is 32 and the number of channels in the synthesis filter bank is 64.

10. A method performed by an signal processing device for filtering an audio signal, the method comprising:

filtering real-valued time domain input audio samples with an analysis filter bank to generate complex valued subband samples;

shifting a phase of the complex-valued subband samples by an amount;

generating modified complex valued subband samples through a high frequency reconstruction process or a parametric stereo process;

unshifting a phase of the modified complex-valued subband samples by the amount;

filtering the modified complex valued subband samples with a synthesis filter bank to generate time domain output audio samples,

wherein the analysis filter bank comprises analysis filters (h_k(n)) that are complex exponential modulated versions of a prototype filter (p₀(n)) according to;

11. A non-transitory computer readable medium containing instructions that when executed by a processor perform the method of claim 10.