Method for reduction of aliasing introduced by spectral envelope adjustment in real-valued filterbanks
First Claim
1. Apparatus for performing gain adjustment on a plurality of audio sub band signals generated by filtering an audio signal using a filter bank, the filter bank having sub band filters, adjacent sub band filters of the filterbank having transition bands overlapping in an overlapping range, comprising:
- an analyzer for analysing the plurality of audio sub band signals generated by filtering the signal using the filter bank to determine, whether a subband signal of a sub band filter and a sub band signal of an adjacent sub band filter have aliasing generating signal components in the overlapping range between the sub band filter and the adjacent sub band filter to obtain grouped audio sub band signals;
a calculator configured for calculating a first gain adjustment value and a second gain adjustment value for the grouped adjacent audio sub band signals comprising an audio sub band signal and an adjacent audio sub band signal, wherein the calculator is operativeto determine a first energy measure indicating a signal energy of the audio sub band signal and a second energy measure indicating a signal energy of the adjacent audio sub band signal,to determine an indication of a reference energy for the grouped adjacent audio sub band signals as a linear combination of a first reference energy value for the audio sub band signal and a second reference energy value for the adjacent audio sub band signal, andto determine an energy estimate for an energy in the grouped adjacent audio sub band signals as a linear combination of the first energy measure for the audio sub band signal and the second energy measure for the adjacent audio sub band signal, andto calculate the first gain adjustment value and the second gain adjustment value for the grouped adjacent audio sub band signals based on the linear combination of the first reference energy value for the audio sub band signal and the second reference energy value for the adjacent audio sub band signal and based on the linear combination of the first energy measure for the audio sub band signal and the second energy measure for the adjacent audio sub band signal; and
a gain adjuster configured for applying the first gain adjustment value to the audio sub band signal of the grouped adjacent audio sub band signals and for applying the second gain adjustment value to the adjacent audio sub band signal of the grouped adjacent audio sub band signals,wherein one or more of the analyzer, the calculator, and the gain adjuster is implemented, at least in part, by one or more hardware elements of the apparatus.
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Abstract
The present invention proposes a new method for improving the performance of a real-valued filterbank based spectral envelope adjuster. By adaptively locking the gain values for adjacent channels dependent on the sign of the channels, as defined in the application, reduced aliasing is achieved. Furthermore, the grouping of the channels during gain-calculation, gives an improved energy estimate of the real valued subband signals in the filterbank.
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Citations
18 Claims
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1. Apparatus for performing gain adjustment on a plurality of audio sub band signals generated by filtering an audio signal using a filter bank, the filter bank having sub band filters, adjacent sub band filters of the filterbank having transition bands overlapping in an overlapping range, comprising:
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an analyzer for analysing the plurality of audio sub band signals generated by filtering the signal using the filter bank to determine, whether a subband signal of a sub band filter and a sub band signal of an adjacent sub band filter have aliasing generating signal components in the overlapping range between the sub band filter and the adjacent sub band filter to obtain grouped audio sub band signals; a calculator configured for calculating a first gain adjustment value and a second gain adjustment value for the grouped adjacent audio sub band signals comprising an audio sub band signal and an adjacent audio sub band signal, wherein the calculator is operative to determine a first energy measure indicating a signal energy of the audio sub band signal and a second energy measure indicating a signal energy of the adjacent audio sub band signal, to determine an indication of a reference energy for the grouped adjacent audio sub band signals as a linear combination of a first reference energy value for the audio sub band signal and a second reference energy value for the adjacent audio sub band signal, and to determine an energy estimate for an energy in the grouped adjacent audio sub band signals as a linear combination of the first energy measure for the audio sub band signal and the second energy measure for the adjacent audio sub band signal, and to calculate the first gain adjustment value and the second gain adjustment value for the grouped adjacent audio sub band signals based on the linear combination of the first reference energy value for the audio sub band signal and the second reference energy value for the adjacent audio sub band signal and based on the linear combination of the first energy measure for the audio sub band signal and the second energy measure for the adjacent audio sub band signal; and a gain adjuster configured for applying the first gain adjustment value to the audio sub band signal of the grouped adjacent audio sub band signals and for applying the second gain adjustment value to the adjacent audio sub band signal of the grouped adjacent audio sub band signals, wherein one or more of the analyzer, the calculator, and the gain adjuster is implemented, at least in part, by one or more hardware elements of the apparatus. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. Method of performing gain adjustment on a plurality of audio sub band signals generated by filtering an audio signal using a filter bank, the filter bank having audio sub band filters, adjacent audio sub band filters of the filter bank having transition bands overlapping in an overlapping range, comprising:
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analysing the plurality of audio sub band signals generated by filtering the signal using the filter bank to determine, whether a subband signal of a sub band filter and a sub band signal of an adjacent sub band filter have aliasing generating signal components in the overlapping range between the sub band filter and the adjacent sub band filter to obtain grouped audio sub band signals; calculating a first gain adjustment value and a second gain adjustment value for the grouped adjacent audio sub band signals comprising an audio sub band signal and an adjacent audio sub band signal, wherein the calculating comprises; determining a first energy measure indicating a signal energy of the audio sub band signal and a second energy measure indicating a signal energy of the adjacent audio sub band signal, determining an indication of a reference energy for the grouped adjacent audio sub band signals as a linear combination of a first reference energy value for the audio sub band signal and a second reference energy value for the adjacent audio sub band signal, determining an energy estimate for an energy in the grouped adjacent audio sub band signals as a linear combination of the first energy measure for the audio sub band signal and the second energy measure for the adjacent audio sub band signal, and calculating the first gain adjustment value and the second gain adjustment value for the grouped adjacent audio sub band signals based on the linear combination of the first reference energy value for the audio sub band signal and the second reference energy value for the adjacent audio sub band signal and based on the linear combination of the first energy measure for the audio sub band signal and the second energy measure for the adjacent audio sub band signal; and applying the first gain adjustment value to the audio sub band signal of the grouped adjacent audio sub band signals and applying the second gain adjustment value to the adjacent audio sub band signal of the grouped adjacent audio sub band signals, wherein one or more of analyzing the plurality of audio sub band signals, calculating a first gain adjustment value, and applying the first gain adjustment value is implemented, at least in part, by one or more hardware elements of an audio signal processing device.
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18. A non-transitory storage medium having stored thereon a computer program having a program code for performing, when the computer program runs on a computer, a method of performing gain adjustment on a plurality of audio sub band signals generated by filtering an audio signal using a filter bank, the filter bank having audio sub band filters, adjacent audio sub band filters of the filter bank having transition bands overlapping in an overlapping range, the method comprising:
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analysing the plurality of audio sub band signals generated by filtering the signal using the filter bank to determine, whether a subband signal of a sub band filter and a sub band signal of an adjacent sub band filter have aliasing generating signal components in the overlapping range between the sub band filter and the adjacent sub band filter to obtain grouped audio sub band signals; calculating a first gain adjustment value and a second gain adjustment value for grouped adjacent audio sub band signals comprising an audio sub band signal and an adjacent audio sub band signal, wherein the calculating comprises; determining a first energy measure indicating a signal energy of the audio sub band signal and a second energy measure indicating a signal energy of the adjacent audio sub band signal, determining an indication of a reference energy for the grouped adjacent audio sub band signals as a linear combination of a first reference energy value for the audio sub band signal and a second reference energy value for the adjacent audio sub band signal, determining an energy estimate for an energy in the grouped adjacent audio sub band signals as a linear combination of the first energy measure for the audio sub band signal and the second energy measure for the adjacent audio sub band signal, and calculating the first gain adjustment value and the second gain adjustment value for the grouped adjacent audio sub band signals based on the linear combination of the first reference energy value for the audio sub band signal and the second reference energy value for the adjacent audio sub band signal and based on the linear combination of the first energy measure for the audio sub band signal and the second energy measure for the adjacent audio sub band signal; and applying the first gain adjustment value to the audio sub band signal of the grouped adjacent audio sub band signals and applying the second gain adjustment value to the adjacent audio sub band signal of the grouped adjacent audio sub band signals.
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Specification