Method for reduction of aliasing introduced by spectral envelope adjustment in real-valued filterbanks
First Claim
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1. Apparatus for audio spectral envelope adjustment of an audio signal, comprising one or more processors that:
- provide a plurality of audio subband signals,an audio subband signal having associated therewith a channel number k indicating an audio frequency range covered by the audio subband signal, the audio subband signal originating from a channel filter having the channel number k in an analysis filterbank having a plurality of channel filters, wherein the channel filter having the channel number k has a channel response which is overlapped with a channel response of an adjacent channel filter having a channel number k-1 in an overlapping range;
examine the audio subband signal having associated therewith the channel number k and examine an adjacent audio subband signal having associated therewith the channel number k-1 to determine, whether the audio subband signal and the adjacent audio subband signal have aliasing generating audio signal components in the overlapping range;
calculate a first gain adjustment value and a second gain adjustment value for the audio subband signal and the adjacent audio subband signal in response to a positive result of the examiner, wherein the calculating comprises determining the first gain adjustment value and the second gain adjustment value dependent on each other, and wherein the calculating comprises calculating the first gain adjustment value and the second gain adjustment value based on an average audio energy of the audio subband signal and the adjacent audio subband signal; and
gain adjust the audio subband signal and the adjacent audio subband signal using the first and the second gain adjustment values to obtain an envelope adjusted audio signal or output the first and the second gain adjustment values for transmission or storing.
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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.
161 Citations
19 Claims
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1. Apparatus for audio spectral envelope adjustment of an audio signal, comprising one or more processors that:
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provide a plurality of audio subband signals, an audio subband signal having associated therewith a channel number k indicating an audio frequency range covered by the audio subband signal, the audio subband signal originating from a channel filter having the channel number k in an analysis filterbank having a plurality of channel filters, wherein the channel filter having the channel number k has a channel response which is overlapped with a channel response of an adjacent channel filter having a channel number k-1 in an overlapping range; examine the audio subband signal having associated therewith the channel number k and examine an adjacent audio subband signal having associated therewith the channel number k-1 to determine, whether the audio subband signal and the adjacent audio subband signal have aliasing generating audio signal components in the overlapping range; calculate a first gain adjustment value and a second gain adjustment value for the audio subband signal and the adjacent audio subband signal in response to a positive result of the examiner, wherein the calculating comprises determining the first gain adjustment value and the second gain adjustment value dependent on each other, and wherein the calculating comprises calculating the first gain adjustment value and the second gain adjustment value based on an average audio energy of the audio subband signal and the adjacent audio subband signal; and gain adjust the audio subband signal and the adjacent audio subband signal using the first and the second gain adjustment values to obtain an envelope adjusted audio signal or output the first and the second gain adjustment values for transmission or storing. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method of audio spectral envelope adjustment of an audio signal, comprising:
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providing a plurality of audio subband signals, an audio subband signal having associated therewith a channel number k indicating the frequency range covered by the audio subband signal, the audio subband signal originating from a channel filter having the channel number k in an analysis filterbank having a plurality of channel filters, wherein the channel filter having the channel number k has a channel response which is overlapped with a channel response of an adjacent channel filter having a channel number k-1 in an overlapping range; examining the audio subband signal having associated therewith the channel number k and examining an adjacent audio subband signal having associated therewith the channel number k-1 to determine, whether the audio subband signal and the adjacent audio subband signal have aliasing generating signal components in the overlapping range; calculating a first gain adjustment value and a second gain adjustment value for the audio subband signal and the adjacent audio subband signal in response to a positive result of the examining, wherein the calculating comprises determining the first gain adjustment value and the second gain adjustment value dependent on each other, wherein the calculating comprises calculating the first gain adjustment value and the second gain adjustment value based on an average audio energy of the audio subband signal and the adjacent audio subband signal; and gain adjusting the audio subband signal and the adjacent audio subband signal using the first and the second gain adjustment values to obtain an envelope adjusted audio signal or outputting the first and the second gain adjustment values for transmission or storing, wherein one or more of the providing, the analysis filterbank, the examining, the calculating, the gain adjusting and the outputting is implemented, at least in part, by one or more hardware elements of an audio signal processing device.
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19. A non-transitory storage medium having stored thereon a computer program having a program code for performing when running on a computer, the method of audio spectral envelope adjustment of an audio signal, the method comprising:
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providing a plurality of audio subband signals, an audio subband signal having associated therewith a channel number k indicating the frequency range covered by the audio subband signal, the audio subband signal originating from a channel filter having the channel number k in an analysis filterbank having a plurality of channel filters, wherein the channel filter having the channel number k has a channel response which is overlapped with a channel response of an adjacent channel filter having a channel number k-1 in an overlapping range; examining the audio subband signal having associated therewith the channel number k and examining an adjacent audio subband signal having associated therewith the channel number k-1 to determine, whether the audio subband signal and the adjacent audio subband signal have aliasing generating signal components in the overlapping range; calculating a first gain adjustment value and a second gain adjustment value for the audio subband signal and the adjacent audio subband signal in response to a positive result of the examining, wherein the calculating comprises determining the first gain adjustment value and the second gain adjustment value dependent on each other, wherein the calculating comprises calculating the first gain adjustment value and the second gain adjustment value based on an average audio energy of the audio subband signal and the adjacent audio subband signal; and gain adjusting the audio subband signal and the adjacent audio subband signal using the first and the second gain adjustment values to obtain an envelope adjusted audio signal or outputting the first and the second gain adjustment values for transmission or storing.
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Specification