Audio encoding/decoding with aliasing switch for domain transforming of adjacent sub-blocks before and subsequent to windowing

• US 8,862,480 B2
• Filed: 01/11/2011
• Issued: 10/14/2014
• Est. Priority Date: 07/11/2008
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Fuchs, Guillaume, Lecomte, Jeremie, Bayer, Stefan, Geiger, Ralf, Multrus, Markus, Schuller, Gerald, Hirschfeld, Jens
• Primary Examiner(s): Lerner, Martin
• Application Number:
  US13/004,351
• Publication Number:
  US 20110173009A1
• Time in Patent Office: 1,372 Days
• Field of Search: 704/203, 704/205, 704/500, 704/501, 704/219
• US Class Current: 704/501
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• CPC Class Codes: G10L 19/04 using predictive techniques
• CPC Class Codes: G10L 19/20 using sound class specific coding, hybrid encoders or object based coding

Abstract

An apparatus for encoding an audio signal includes the windower for windowing a first block of the audio signal using an analysis window having an aliasing portion and a further portion. The apparatus furthermore includes a processor for processing the first sub-block of the audio signal associated with the aliasing portion by transforming the sub-block from a domain into a different domain subsequent to windowing the first sub-block to obtain the processed first sub-block, and for processing a second sub-block of the audio signal associated with the further portion by transforming the second sub-block from the domain into the different domain before windowing the second sub-block to obtain a processed second sub-block. Thus, a critically sampled switch between two coding modes can be obtained.

Claims

1. Apparatus for encoding an audio signal, comprising:

a windower for windowing a first block of the audio signal using an analysis window, the analysis window comprising an aliasing portion, and a further portion;

a processor for processing a first sub-block of the audio signal associated with the aliasing portion by transforming the first sub-block into a different domain from a domain, in which the audio signal is, subsequent to windowing the first sub-block to acquire a processed first sub-block, and for processing a second sub-block of the audio signal associated with the further portion by transforming the second sub-block into the different domain before windowing the second sub-block to acquire a processed second sub-block; and

a transformer for converting the processed first sub-block and the processed second sub-block from the different domain into a further domain using a block transform rule to acquire a converted first block,

wherein the apparatus is configured for further processing the converted first block using a data compression algorithm.

2. Apparatus in accordance with claim 1, which is configured for processing a second block of the audio signal overlapping with the first block using a second analysis window comprising a further aliasing portion corresponding to the aliasing portion of the first analysis window.

3. Apparatus in accordance with claim 1, in which the domain, in which the audio signal is positioned, is a time domain, in which the different domain is an LPC domain, in which a third domain, in which a second block of the audio signal overlapping with the first block of the audio signal is encoded, is a frequency domain, and in which the further domain, in which the transformer is configured for transforming, is an LPC frequency domain, and

wherein the processor comprises an LPC filter for transforming from the first domain to the second domain, or wherein the transformer comprises a Fourier-based conversion algorithm for transforming input data into the frequency domain of the input data such as a DCT, a DST, an FFT, or a DFT.

4. Apparatus in accordance with claim 1, in which the windower comprises a folding function for folding input values to acquire output values, the number of output values being smaller than the number of input values, wherein the folding function is such that time aliasing is introduced into the output values.

5. Apparatus in accordance with claim 1, in which the windower is operative to perform the windowing to acquire the input values for a subsequently performed folding function.

6. Apparatus in accordance with claim 1, in which the apparatus comprises a first encoding branch for encoding the audio signal in a frequency domain, and a second encoding branch for encoding the audio signal based on a further frequency domain, the further frequency domain being different from the frequency domain,

wherein the second encoding branch comprises a first sub-branch for encoding the audio signal in the further frequency domain, and a second sub-branch for encoding the audio signal in a third domain different from the further frequency domain, the apparatus further comprising a decision stage for deciding, whether a block of audio data is represented in an output bit stream by data generated using the first encoding branch or the first sub-branch or the second sub-branch of the second encoding branch, and

wherein the processor is configured for controlling the decision stage to decide in favor of the first sub-branch, when the transition from the first encoding branch to the second encoding branch or from the second encoding branch to the first encoding branch is to be performed.

7. Apparatus in accordance with claim 1, in which the further portion comprises a further non-aliasing portion and an additional aliasing portion or an even further aliasing portion overlapping with a corresponding aliasing portion of a neighboring block of the audio signal.

8. Apparatus for decoding an encoded audio signal comprising an encoded first block of audio data, the encoded block comprising an aliasing portion and a further portion, comprising:

a processor for processing the aliasing portion by transforming the aliasing portion into a target domain before performing a synthesis windowing to acquire a windowed aliasing portion, and for performing a synthesis windowing of the further portion before performing a transform into the target domain; and

a time domain aliasing canceller for combining the windowed aliasing portion and a further windowed aliasing portion of an encoded second block of audio data subsequent to the transform of the aliasing portion of the encoded first block of audio data into the target domain to acquire a decoded audio signal corresponding to the aliasing portion of the first block.

9. Apparatus in accordance with claim 8,

in which the processor comprises a transformer for converting the aliasing portion from a fourth domain into a second domain, and wherein the processor furthermore comprises a further transformer for converting the aliasing portion represented in the second domain into a first domain, wherein the transformer or the further transformer is operative to perform a block-based frequency time conversion algorithm.

10. Apparatus in accordance with claim 8, in which the processor is operative to perform an unfolding operation for acquiring output data comprising a number of values larger than a number of values input into the unfolding operation.

11. Apparatus in accordance with claim 8, in which the processor is operative to use a synthesis windowing function being related to an analysis window function used when generating the encoded audio signal.

12. Apparatus in accordance with claim 8, in which the encoded audio signal comprises a coding mode indicator indicating a coding mode for the encoded first block and the encoded second block,

wherein the apparatus further comprises a transition controller for controlling the processor, when the coding mode indicator indicates a coding mode change from a first coding mode to a different second coding mode or vice versa, and for controlling the processor to perform a single operation for a complete encoding block, when the coding mode change between two encoding blocks is not signaled.

13. Apparatus in accordance with claim 8,

in which a first coding mode and a second coding mode comprise an entropy decoding stage, a dequantizing stage, a frequency-time converting stage comprising an unfolding operation, and a synthesis windowing stage,

in which the time domain aliasing canceller comprises an adder for adding corresponding aliasing portions of encoded blocks acquired by the synthesis windowing stage, the corresponding aliasing portions being acquired by an overlapping processing of the audio signal, and

in which, in the first coding mode, the time domain aliasing canceller is configured for adding portions of blocks acquired by the synthesis windowing to acquire, as an output of the addition, the decoded signal in the target domain, and

in which, in the second coding mode, the output of the addition is processed by the processor to perform a transform of the output of the addition to the target domain.

14. Method of encoding an audio signal, comprising:

windowing, by a windower, a first block of the audio signal using an analysis window, the analysis window comprising an aliasing portion, and a further portion;

processing, by a processor, a first sub-block of the audio signal associated with the aliasing portion by transforming the first sub-block into a different domain from a domain, in which the audio signal is, subsequent to windowing the first sub-block to acquire a processed first sub-block;

processing, by the processor, a second sub-block of the audio signal associated with the further portion by transforming the second sub-block into the different domain before windowing the second sub-block to acquire a processed second sub-block;

converting, by a converter, the processed first sub-block and the processed second sub-block from the different domain into a further domain using a block transform rule to acquire a converted first block; and

further processing, by the processor, the converted first block using a data compression algorithm,

wherein at least one of the processor and the converter comprises a hardware implementation.

15. Method of decoding an encoded audio signal comprising an encoded first block of audio data, the encoded block comprising an aliasing portion and a further portion, comprising:

processing, by a processor, the aliasing portion by transforming the aliasing portion into a target domain before performing a synthesis windowing to acquire a windowed aliasing portion;

a further portion synthesis windowing, by a synthesis windower, of the further portion before performing a transform into the target domain; and

combining, by a combiner, the windowed aliasing portion and a further windowed aliasing portion of an encoded second block of audio data to acquire a time-domain aliasing cancellation, subsequent to the transform of the aliasing portion of the encoded first block of audio data into the target domain to acquire a decoded audio signal corresponding to the aliasing portion of the first block,

wherein at least one of the processor, the synthesis windower and the combiner comprises a hardware implementation.

16. Non-transitory storage medium having stored thereon a computer program comprising a program code for performing, when running on a computer, the method for encoding an audio signal, the method comprising:

windowing a first block of the audio signal using an analysis window, the analysis window comprising an aliasing portion, and a further portion;

processing a first sub-block of the audio signal associated with the aliasing portion by transforming the first sub-block into a different domain from a domain, in which the audio signal is, subsequent to windowing the first sub-block to acquire a processed first sub-block;

processing a second sub-block of the audio signal associated with the further portion by transforming the second sub-block into the different domain before windowing the second sub-block to acquire a processed second sub-block;

converting the processed first sub-block and the processed second sub-block from the different domain into a further domain using a block transform rule to acquire a converted first block; and

further processing the converted first block using a data compression algorithm.

17. Non-transitory storage medium having stored thereon a computer program comprising a program code for performing, when running on a computer, the method of decoding an encoded audio signal comprising an encoded first block of audio data, the encoded block comprising an aliasing portion and a further portion, the method comprising:

processing the aliasing portion by transforming the aliasing portion into a target domain before performing a synthesis windowing to acquire a windowed aliasing portion;

a further portion synthesis windowing of the further portion before performing a transform into the target domain; and

combining the windowed aliasing portion and a further windowed aliasing portion of an encoded second block of audio data to acquire a time-domain aliasing cancellation, subsequent to the transform of the aliasing portion of the encoded first block of audio data into the target domain to acquire a decoded audio signal corresponding to the aliasing portion of the first block.