Digital filterbank for spectral envelope adjustment
AssigneeDolby International AB
InventorPer Ekstrand
Life of this patent
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Abstract
An apparatus and method are disclosed for processing an audio signal. The apparatus includes an input interface, a digital filterbank having an analysis part and a synthesis part, a first phase shifter, a spectral envelope adjuster, a second phase shifter, and an output interface. The first phase shifter and the second phase shifter reduce a complexity of the digital filterbank, which includes both analysis and synthesis filters that are complex-exponential modulated versions of a prototype filter.
Claims7
A signal processing device for 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 unit that generates modified complex valued subband samples by applying time and frequency varying gains to the complex valued subband samples;
- and
- a synthesis filter bank that receives the modified complex valued subband samples and generates time domain output audio samples,
- wherein the synthesis filter bank comprises synthesis filters (fk(n)) that are complex exponential modulated versions of a prototype filter (p0(n)) according to:
- f
- k
- (
- n
- )
- =
- p
- 0
- (
- n
- )
-
- exp
-
- {
- i
-
- π
- M
-
- (
- k
- +
- 1
- 2
- )
-
- (
- n
- -
- D
- 2
- +
- A
- )
- }
- ,
- 0
- ≤
- n
- <
- N
- ,
- 0
- ≤
- k
- <
- M
- where the synthesis filter bank has M channels, the prototype filter (0(n)) has a length N, the analysis filter bank and the synthesis filter bank have a system delay of D samples that represents a latency of a signal passing through the analysis filter followed by the synthesis filter, with D being smaller than N, and A is a constant chosen to enable efficient implementation of the analysis filter bank.
A method performed by a signal processing device for processing an audio signal, the method comprising:
- receiving real-valued time domain input audio samples;
- filtering the real-valued time domain input audio samples with an analysis filter bank to generate complex valued subband samples;
- generating modified complex valued subband samples by applying time and frequency varying gains to the complex valued subband samples;
- filtering the modified complex valued subband samples with a synthesis filter bank to generate time domain output audio samples,
- wherein the synthesis filter bank comprises synthesis filters (fk(n)) that are complex exponential modulated versions of a prototype filter (p0(n)) according to:
- f
- k
- (
- n
- )
- =
- p
- 0
- (
- n
- )
-
- exp
-
- {
- i
-
- π
- M
-
- (
- k
- +
- 1
- 2
- )
-
- (
- n
- -
- D
- 2
- +
- A
- )
- }
- ,
- 0
- ≤
- n
- <
- N
- ,
- 0
- ≤
- k
- <
- M
- where the synthesis filter bank has M channels, the prototype filter (p0(n)) has a length N, the analysis filter bank and the synthesis filter bank have a system delay of D samples that represents a latency of a signal passing through the analysis filter followed by the synthesis filter, with D being smaller than N, and A is a constant chosen to enable efficient implementation of the analysis filter bank.
Dependencies are inferred from the claim text.