Apparatus and method for processing an input audio signal using cascaded filterbanks

Patent metadata

Field	Value
Publication number	US-9792915-B2
Application number	US-201213604364-A
Country	US
Kind code	B2
Filing date	Sep 5, 2012
Priority date	Mar 9, 2010
Publication date	Oct 17, 2017
Grant date	Oct 17, 2017

Abstract

An apparatus for processing an input audio signal relies on a cascade of filterbanks, the cascade having a synthesis filterbank for synthesizing an audio intermediate signal from the input audio signal, the input audio signal being represented by a plurality of first subband signals generated by an analysis filterbank, wherein a number of filterbank channels of the synthesis filterbank is smaller than a number of channels of the analysis filterbank. The apparatus furthermore has a further analysis filterbank for generating a plurality of second subband signals from the audio intermediate signal, wherein the further analysis filterbank has a number of channels being different from the number of channels of the synthesis filterbank, so that a sampling rate of a subband signal of the plurality of second subband signals is different from a sampling rate of a first subband signal of the plurality of first subband signals.

First claim

The invention claimed is:

1. Apparatus for processing a time discrete input audio signal, comprising:
a synthesis filterbank that receives, as an input, a plurality of time discrete first subband signals representing the time discrete input audio signal and having been generated by an analysis filterbank, and that synthesizes an audio intermediate signal from the input audio signal, wherein a number of filterbank channels of the synthesis filterbank is smaller than a number of channels of the analysis filterbank; and
a further analysis filterbank that receives, as an input, the audio intermediate signal and that generates a plurality of time discrete second subband signals from the audio intermediate signal, wherein the further analysis filterbank comprises a number of channels being different from the number of channels of the synthesis filterbank, and wherein a sampling rate of a time discrete subband signal of the plurality of time discrete second subband signals is different from a sampling rate of a time discrete first subband signal of the plurality of time discrete first subband signals,
wherein the synthesis filterbank is configured for only processing a sub-group of all first subband signals of the plurality of first subband signals representing the full bandwidth input audio signal, and wherein the synthesis filterbank is configured for generating the audio intermediate signal as a band segment of the full bandwidth input audio signal modulated to the base band, and
wherein at least one of the synthesis filterbank and the analysis filterbank comprises a hardware implementation.

2. Apparatus in accordance with claim 1 , in which the synthesis filterbank is a real-valued filterbank.

3. Apparatus in accordance with claim 1 , in which the number of first subband signals of the plurality of first subband signals is greater than or equal to 24, and
in which the number of filterbank channels of the synthesis filterbank is lower than or equal to 22.

4. Apparatus in accordance with claim 1 , in which the number of channels of the further analysis filterbank is greater than the number of channels of the synthesis filterbank.

5. Apparatus in accordance with claim 1 , further comprising:
the analysis filterbank that receives a time domain representation of the input audio signal and that analyses the time domain representation to acquire the plurality of first subband signals, wherein a sub-group of the plurality of first subband signals is input into the synthesis filterbank, and wherein the remaining subband signals of the plurality of first subband signals are not input into the synthesis filterbank.

6. Apparatus in accordance with claim 1 , in which the analysis filterbank is a complex-valued filterbank, in which the synthesis filterbank comprises a real-value calculator for calculating real-valued subband signals from the first subband signals, wherein the real-valued subband signals calculated by the real-value calculator are further processed by the synthesis filterbank to acquire the audio intermediate signal.

7. Apparatus in accordance with claim 1 , in which the further analysis filterbank is a complex-valued filterbank and is configured to generate the plurality of second subband signals as complex subband signals.

8. Apparatus in accordance with claim 1 , in which the synthesis filterbank, the further analysis filterbank or the analysis filterbank are configured to use sub-sampled versions of the same filterbank window.

9. Apparatus in accordance with claim 1 , further comprising:
a subband signal processor that processes the plurality of second subbands; and
a further synthesis filterbank that filters a plurality of processed subbands, wherein the further synthesis filterbank, the synthesis filterbank, the analysis filterbank or the further analysis filterbank are configured to use sub-sampled versions of the same filterbank window, or wherein the further synthesis filterbank is configured to apply a synthesis window, and wherein the further analysis filterbank, the synthesis filterbank or the analysis filterbank are configured to apply a sub-sampled version of the synthesis window used by the further synthesis filterbank.

10. Apparatus in accordance with claim 1 , further comprising a subband processor that performs a non-linear processing operation per subband to acquire a plurality of processed subbands;
a high frequency reconstruction processor that adjusts an input signal, based on transmitted parameters; and
a further synthesis filterbank that combines the input audio signal and the plurality of processed subband signals,
wherein the high frequency reconstruction processor is configured for processing an output of the further synthesis filterbank or for processing the plurality of processed subbands, before the plurality of processed subbands is input into the further synthesis filterbank.

11. Apparatus in accordance with claim 1 , wherein the further analysis filterbank or the synthesis filterbank comprises a prototype window function calculator for calculating a prototype window function by subsampling or interpolating using a stored window function for a filterbank comprising a different size using information on a number of channels for the further analysis filterbank or the synthesis filterbank.

12. Apparatus in accordance with claim 1 , in which the synthesis filterbank is configured for setting to zero an input into a lowest and into a highest filterbank channel of the synthesis filterbank.

13. Apparatus in accordance with claim 1 , being configured for performing a block based harmonic transposition, wherein the synthesis filterbank is a sub-sampled filterbank.

14. Apparatus in accordance with claim 1 , further comprising a subband processor that processes the plurality of second subbands,
wherein the subband processor comprises, in arbitrary orders, a decimator controlled by a bandwidth extension factor, and a stretcher for a subband signal, wherein the stretcher comprises a block extractor that extracts a number of overlapping blocks in accordance with an extracting advance value; a phase adjuster or windower that adjusts subband sampling values in each block based on a window function or a phase correction; and an overlap-adder that performs an overlap-add-processing of windowed and phase adjusted blocks using an overlap advance value greater than the extraction advance value.

15. Apparatus in accordance with claim 1 , further comprising a subband processor, wherein the subband processor comprises:
a plurality of different processing branches for different transposition factors to acquire a transpose signal, wherein each processing branch is configured for extracting blocks of subband samples;
an adder that adds the transpose signals to acquire transpose blocks; and
an overlap-adder that overlap-adds time consecutive transpose blocks using a block advance value being greater than a block advance value used for extracting blocks in the plurality of different processing branches.

16. Apparatus in accordance with claim 1 , further comprising:
the analysis filterbank, wherein the synthesis filterbank and the further analysis filterbank are configured to perform a sample rate conversion,
a time stretch processor that processes the sample rate converted signal; and
a combiner that combines processed subband signals generated by the time stretch processor to acquire a processed time domain signal.

17. Non-transitory storage medium having stored thereon a computer program comprising a program code for performing, when running on a computer, a

Assignees

• Villemoes Lars
• Ekstrand Per
• Disch Sascha
• Nagel Frederik
• Wilde Stephan
• Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E V
• Dolby Int Ab

Inventors

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

Classifications

• G10L21/04

  Time compression or expansion · CPC title

• G10L19/0204 Primary

  using subband decomposition · CPC title

• G10L19/008 Primary

  Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing · CPC title

• G10L21/038

  using band spreading techniques · CPC title

• G10L21/0232 Primary

  Processing in the frequency domain · CPC title