Device and method for improved magnitude response and temporal alignment in a phase vocoder based bandwidth extension method for audio signals

Patent metadata

Field	Value
Publication number	US-9318127-B2
Application number	US-201213604313-A
Country	US
Kind code	B2
Filing date	Sep 5, 2012
Priority date	Mar 9, 2010
Publication date	Apr 19, 2016
Grant date	Apr 19, 2016

Abstract

An apparatus for generating a bandwidth extended audio signal from an input signal, includes a patch generator for generating one or more patch signals from the input signal, wherein the patch generator is configured for performing a time stretching of subband signals from an analysis filterbank, and wherein the patch generator further includes a phase adjuster for adjusting phases of the subband signals using a filterbank-channel dependent phase correction.

First claim

The invention claimed is:

1. An apparatus for generating a bandwidth extended audio signal from an input signal, comprising:
a patch generator for generating one or more patch signals from the input signal, wherein a patch signal comprises a patch center frequency being different from a patch center frequency of a different patch or from a center frequency of the input audio signal,
wherein the patch generator is configured for performing a time stretching of subband signals from an analysis filterbank, and
wherein the patch generator comprises a phase adjuster for adjusting phases of the subband signals using a filterbank-channel dependent phase correction, the filterbank-channel dependent phase correction comprising:
π C ( k+ ½)

wherein k indicates a filterbank channel and C is a real number between 2 and 4.

2. The apparatus in accordance with claim 1 , in which the phase adjuster is configured to select the phase correction so that an amplitude variation of a signal introduced by a design of the filterbank is reduced or eliminated.

3. The apparatus in accordance with claim 1 , in which the phase adjuster is configured for applying the phase correction, the phase correction being independent on the subband signal.

4. The apparatus in accordance with claim 1 , in which the phase adjuster is configured to additionally apply a signal-dependent phase correction depending on an applied transposition factor.

5. The apparatus in accordance with claim 1 , in which the patch generator is configured for performing a block-wise processing and comprises:
a block extractor for extracting subsequent blocks of values from the subband signal using a block advance value;
the phase adjuster; and
an overlap-add processor, wherein the overlap-add processor is configured for applying a block advance value being larger than the block advance value to acquire the time stretching.

6. The apparatus in accordance with claim 5 , in which the block extractor is configured to additionally perform a decimation operation dependent on the transposition factor T and to perform an interpolation in case of a non-integer decimation operation.

7. The apparatus in accordance with claim 5 , in which the patch generator further comprises a windower for windowing a block using a window function.

8. The apparatus in accordance with claim 1 , which is configured for performing a bandwidth extension using at least two transposition factors T, wherein the patch generator is configured:
for the first transposition factor,
to extract using a block advance value and using no or a first decimation using a first decimation factor;
to phase adjust the samples of the block of subband samples;
to zero pad the phase adjusted block to a certain length to acquire a first transpose signal;

for the second transposition factor,
to extract a block of subband samples using a block advance value and using a decimation using a second decimation factor being greater than the first decimation factor, when a first decimation has been performed;
to phase adjust the samples of the block of subband samples; and
to zero pad the phase adjusted block to a certain length to acquire a second transposed signal;

to add the first and the second transposed signal in a sample-by-sample to acquire a transpose block; and
to overlap-add sequential transpose blocks using an advance value being greater than the block advance value to acquire a transposed subband signal.

9. The apparatus in accordance with claim 1 , further comprising:
a high frequency reconstruction processor for applying high frequency reconstruction parameters to the subband signals subsequent to the phase correction applied to the subband signals to acquire adjusted subband signals.

10. The apparatus in accordance with claim 1 , further comprising a synthesis filterbank comprising a subband spacing being greater than a subband spacing of the analysis filterbank.

11. The apparatus in accordance with claim 1 , in which the patch generator comprises an analysis filterbank for generating the subband signals from a lowband signal, wherein the analysis filter bank a Quadrature Mirror Filterbank comprising phase twiddling, and in which the phase correction depends on the transposition factor.

12. The apparatus in accordance with claim 1 , in which the analysis filterbank is a QMF filterbank and is configured to apply a phase twiddling so that the phase correction is independent from a transposition factor used for generating the one or more patched signals.

13. The apparatus in accordance with claim 1 , in which the patch generator comprises a time stretcher, and in which the time stretcher comprises a block extractor using an extraction advance value.

14. The apparatus in accordance with claim 1 , in which the patch generator comprises a time stretcher, wherein the time stretcher comprises a block extractor, a windower, or a phase adjuster and the overlap-adder for at least two different channels comprising different channel numbers of an analysis filterbank,
wherein the windower or phase adjuster for each of the at least two channels is configured for applying a phase adjustment for each channel, the phase adjustment depending on the channel number.

15. The apparatus in accordance with claim 1 , in which the phase adjuster is configured for applying a phase adjustment to sampling values of a block of sampling values, the phase adjustment being a combination of a phase value depending on the time stretching amount and on an actual phase of the block, and a signal-independent phase value depending on the channel number as the phase correction.

16. The apparatus in accordance with claim 1 , in which the patch generator is configured to generate the one or more patch signals so that a time disalignment between the input audio signal and the one or more patch signals or a time disalignment between different patch signals is reduced or eliminated.

17. The apparatus in accordance with claim 1 , in which the patch generator comprises a plurality of patches, at least one patcher comprising a decimating functionality, a time stretching functionality and a patch corrector for applying a time correction to the patch signals to reduce or eliminate the time disalignment.

18. A method of generating a bandwidth extended audio signal from an input signal, comprising:
generating one or more patch signals from the input signal, wherein a patch signal comprises a patch center frequency being different from a patch center frequency of a different patch or from a center frequency of the input audio signal,
wherein a time stretching of subband signals from an analysis filterbank is performed, and
wherein phases of the subband signals are adjusted using a filterbank-channel dependent phase correction, the filterbank-channel dependent phase correction comprising:
π C ( k+ ½)

wherein k indicates a filterbank channel and C is a real number between 2 and 4.

19. A non-transitory storage medium having stored thereon a computer program comprising a program code for performing, when running in a computer, the method of generating a bandwidth extended audio signal from an input signal, the method comprising:
generating one or more patch signals from the input signal, wherein a patch signal comprises a patch center frequency being different from a patch center frequency of a different patch or from a center frequency of the input audio signal,
wherein a time stretching of subband signals from an analysis filterbank is performed, and
wherein phas

Assignees

• Disch Sascha
• Nagel Frederik
• Wilde Stephan
• Villemoes Lars
• Ekstrand Per
• Fraunhofer Ges Forschung
• Dolby Int Ab

Inventors

• Disch Sascha
• Nagel Frederik
• Wilde Stephan
• Villemoes Lars
• Ekstrand Per

Classifications

• G10L21/038 Primary

  using band spreading techniques · CPC title

• G10L21/02 Primary

  Speech enhancement, e.g. noise reduction or echo cancellation (reducing echo effects in line transmission systems H04B3/20; echo suppression in hands-free telephones H04M9/08) · CPC title

• G10L19/26

  Pre-filtering or post-filtering · CPC title

• G10L19/0208 Primary

  Subband vocoders · CPC title

• G10L19/022

  Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring · CPC title