Method for reduction of aliasing introduced by spectral envelope adjustment in real-valued filterbanks
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.
1. Apparatus for spectral envelope adjustment of a signal, comprising:
a provider for providing a plurality of subband signals, a subband signal having associated therewith a channel number k indicating a frequency range covered by the subband signal, the subband signal originating from a channel filter having the channel number k in an analysis filter-bank 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;
an examiner for examining the subband signal having associated therewith the channel number k and for examining an adjacent subband signal having associated therewith the channel number k−1 to determine, whether the subband signal and the adjacent subband signal have aliasing generating signal components in the overlapping range,
wherein the examiner is operative to calculate signs of subband signals based on coefficients of prediction polynomials for the subband signal and the adjacent subband signal, and to indicate a positive result, the positive result being that the subband signal and the adjacent subband signal have aliasing generating signal components in the overlapping range, when the signs have a predetermined relationship to each other,
a calculator for calculating a first gain adjustment value and a second gain adjustment value for the subband signal and the adjacent subband signal in response to the positive result of the examiner, wherein the calculator is operative to determine the first gain adjustment value and the second gain adjustment value dependent on each other; and
a gain adjuster for gain adjusting the subband signal and the adjacent subband signal using the first and the second gain adjusting values or an output for outputting the first and the second gain adjustment values for transmission or storing, wherein the provider, the examiner, the calculator or the gain adjuster comprises a hardware implementation.
2. Apparatus in accordance with claim 1 , in which the examiner is operative to apply an auto-correlation method or a co-variance method.
3. Apparatus in accordance with claim 1 , in which the prediction polynomial is a low order polynomial having a first order coefficient, wherein the order of the low order polynomial is smaller than 4 and in which the examiner is operative to use the first order coefficient for calculating the signs of the subband signals.
4. Apparatus in accordance with claim 1 , in which the predetermined relationship is defined such that the subband signal having associated therewith the channel number k has a first sign and the adjacent subband signal having associated therewith the channel number k−1 has a second sign, which is opposite to the first sign.
5. Apparatus in accordance with claim 4 , in which the first sign is negative, and the second sign is positive.
6. Apparatus in accordance with claim 1 , in which the examiner is operative to perform a tonal analysis for the subband signal and the adjacent subband signal for determining a tonal component having a tonality measure above a tonality threshold.
7. Apparatus in accordance with claim 6 , in which the examiner is operative to determine, whether the tonal component is in the overlapping range of channel k and channel k−1.
8. Apparatus in accordance with claim 1 , further comprising a further provider for providing a first reference spectral envelope value for the subband signal and a second reference spectral envelope value for the adjacent subband signal,
in which the calculator is operative to determine a first energy measure indicating a signal energy of the subband signal and a second energy measure indicating a signal energy of the adjacent subband signal, and
in which the examiner is further operative to calculate the first and the second gain adjustment values based on a linear combination of the first reference spectral envelope value and the second reference spectral envelope value or a linear combination of the first energy measure or the second energy measure.
9. Apparatus in accordance with claim 1 , in which the calculator is operative to calculate the first and the second gain adjustment values such that they differ by less than a predetermined threshold or are equal to each other.
10. Apparatus in accordance with claim 9 , in which the predetermined threshold is lower than or equal to 6 dB.
11. Apparatus in accordance with claim 1 , further comprising a further provider for providing an unmodified first gain adjustment value for the subband signal and an unmodified second gain adjustment value for the adjacent subband signal, and
in which the calculator is operative to calculate the first and the second gain adjustment values so that both are larger than or equal to a lower value of the first and the second unmodified gain adjustment values and smaller or equal to a higher value of the first and the second unmodified gain adjustment values.
12. Apparatus in accordance with claim 11 , in which the unmodified first gain adjustment value and the unmodified second gain adjustment value are indicative for a spectral envelope of an original signal in a frequency band, wherein the frequency band is to be reconstructed by a spectral band replication.
13. Apparatus in accordance with claim 1 , further comprising a synthesis filterbank for filtering the gain adjusted subband signals to obtain a synthesized output signal.
14. Apparatus in accordance with claim 1 , in which the analysis filterbank is a real valued filterbank, and
in which the synthesis filterbank is a real valued filterbank.
15. Apparatus in accordance with claim 1 , in which the analysis filterbank is a complex-valued filterbank, and in which the synthesis filterbank is a real-valued filterbank.
16. Apparatus in accordance with claim 1 , in which the calculator is operative to calculate the first gain adjustment value and the second gain adjustment value based on an average energy of the subband signal and the adjacent subband signal.
17. Apparatus for spectral envelope adjustment of a signal, comprising:
a provider for providing a plurality of subband signals, a subband signal having associated therewith a channel number k indicating a frequency range covered by the subband signal, the 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;
an examiner for examining the subband signal having associated therewith the channel number k and for examining an adjacent subband signal having associated therewith the channel number k−1 to determine, whether the subband signal and the adjacent subband signal have aliasing generating signal components in the overlapping range;
a further provider for providing an unmodified first gain adjustment value for the subband signal and an unmodified second gain adjustment value for the adjacent subband signal;
a calculator for calculating a first gain adjustment value and a second gain adjustment value for the subband signal and the adjacent subband signal in response to a positive result of the examiner, the positive result being that the subband signal and the adjacent subband signal have aliasing generating signal components in the overlapping range, wherein the calculator is operative to determine the first gain adjustment value and the second gain adjustment value dependent on each other,
wherein the calculator is operative to calculate the first and the second gain adjustment values so that both are larger than or equal to a lower value of the first and the second unmodified gain adjustment values and smaller or equal to a higher value of the first and the second unmodified gain adjustment values; and
a gain adjuster for gain adjusting the subband signal and the adjacent subband signal using the first and the second gain adjusting values or an output for outputting the first and the second gain adjustment values for transmission or storing,
wherein the provider, the examiner, the further provider, the calculator or the gain adjuster comprises a hardware implementation.
18. Apparatus for spectral envelope adjustment of a signal, comprising:
a provider for providing a plurality of subband signals, a subband signal having associated therewith a channel number k indicating a frequency range covered by the subband signal, the 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;
an examiner for examining the subband signal having associated therewith the channel number k and for examining an adjacent subband signal having associated therewith the channel number k−1 to determine, whether the subband signal and the adjacent subband signal have aliasing generating signal components in the overlapping range;
a calculator for calculating a first gain adjustment value and a second gain adjustment value for the subband signal and the adjacent subband signal in response to a positive result of the examiner, the positive result being that the subband signal and the adjacent subband signal have aliasing generating signal components in the overlapping range, wherein the calculator is operative to determine the first gain adjustment value and the second gain adjustment value dependent on each other,
wherein the calculator is operative to calculate the first gain adjustment value and the second gain adjustment value based on an average energy of the subband signal and the adjacent subband signal; and
a gain adjuster for gain adjusting the subband signal and the adjacent subband signal using the first and the second gain adjusting values or an output for outputting the first and the second gain adjustment values for transmission or storing,
wherein the provider, the examiner, the calculator or the gain adjuster comprises a hardware implementation.
19. Method of spectral envelope adjustment of a signal, comprising:
providing a plurality of subband signals, a subband signal having associated therewith a channel number k indicating a frequency range covered by the subband signal, the 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 subband signal having associated therewith the channel number k and examining an adjacent subband signal having associated therewith the channel number k−1 to determine, whether the subband signal and the adjacent subband signal have aliasing generating signal components in the overlapping range;
providing an unmodified first gain adjustment value for the subband signal and an unmodified second gain adjustment value for the adjacent subband signal;
calculating a first gain adjustment value and a second gain adjustment value for the subband signal and the adjacent subband signal in response to a positive result of the examining, the positive result being that the subband signal and the adjacent subband signal have aliasing generating signal components in the overlapping range,
wherein, in the calculating, the first and the second gain adjustment values are calculated so that both are larger than or equal to a lower value of the first and the second unmodified gain adjustment values and smaller or equal to a higher value of the first and the second unmodified gain adjustment values; and
gain adjusting the subband signal and the adjacent subband signal using the first and the second gain adjusting values or outputting the first and the second gain adjustment values for transmission or storing, wherein the method comprises a hardware implementation.
20. Method of spectral envelope adjustment of a signal, comprising:
providing a plurality of subband signals, a subband signal having associated therewith a channel number k indicating a frequency range covered by the subband signal, the 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 subband signal having associated therewith the channel number k and for examining an adjacent subband signal having associated therewith the channel number k−1 to determine, whether the subband signal and the adjacent 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 subband signal and the adjacent subband signal in response to a positive result of the examining, the positive result being that the subband signal and the adjacent subband signal have aliasing generating signal components in the overlapping range,
wherein, in the calculating, the first gain adjustment value and the second gain adjustment value are calculated based on an average energy of the subband signal and the adjacent subband signal; and
gain adjusting the subband signal and the adjacent subband signal using the first and the second gain adjusting values or outputting the first and the second gain adjustment values for transmission or storing,
wherein the method comprises a hardware implementation.
21. A non-transitory storage medium having stored thereon a computer program having a program code for performing a method of spectral envelope adjustment of a signal, when the computer program runs on a computer, the method comprising:
providing a plurality of subband signals, a subband signal having associated therewith a channel number k indicating a frequency range covered by the subband signal, the 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 subband signal having associated therewith the channel number k and for examining an adjacent subband signal having associated therewith the channel number k−1 to determine, whether the subband signal and the adjacent subband signal have aliasing generating signal components in the overlapping range;
providing an unmodified first gain adjustment value for the subband signal and an unmodified second gain adjustment value for the adjacent subband signal;
calculating a first gain adjustment value and a second gain adjustment value for the subband signal and the adjacent subband signal in response to a positive result of the examining, the positive result being that the subband signal and the adjacent subband signal have aliasing generating signal components in the overlapping range,
wherein, in the calculating, the first and the second gain adjustment values are calculated so that both are larger than or equal to a lower value of the first and the second unmodified gain adjustment values and smaller or equal to a higher value of the first and the second unmodified gain adjustment values; and
gain adjusting the subband signal and the adjacent subband signal using the first and the second gain adjusting values or outputting the first and the second gain adjustment values for transmission or storing.
22. A non-transitory storage medium having stored thereon a computer program having a program code for performing a method of spectral envelope adjustment of a signal, when the computer program runs on a computer, the method comprising:
providing a plurality of subband signals, a subband signal having associated therewith a channel number k indicating a frequency range covered by the subband signal, the 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 subband signal having associated therewith the channel number k and for examining an adjacent subband signal having associated therewith the channel number k−1 to determine, whether the subband signal and the adjacent 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 subband signal and the adjacent subband signal in response to a positive result of the examining, the positive result being that the subband signal and the adjacent subband signal have aliasing generating signal components in the overlapping range,
wherein, in the calculating, the first gain adjustment value and the second gain adjustment value are calculated based on an average energy of the subband signal and the adjacent subband signal; and
gain adjusting the subband signal and the adjacent subband signal using the first and the second gain adjusting values or outputting the first and the second gain adjustment values for transmission or storing.