Apparatus and Method for Encoding/Decoding an Audio Signal Using an Aliasing Switch Scheme

• US 20110173009A1
• Filed: 01/11/2011
• Published: 07/14/2011
• 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: Hirschfeld, Jens, Schuller, Gerald, Geiger, Ralf, Fuchs, Guillaume, Multrus, Markus, Bayer, Stefan, Lecomte, Jeremie
• Granted Patent: US 8,862,480 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• 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. The apparatus furthermore includes a transformer for converting the processed first sub-block and the processed second sub-block from the different domain into a further different domain using the same block transform rule to obtain a converted first block which may then be compressed using any of the well-known data compression algorithms. Thus, a critically sampled switch between two coding modes can be obtained, since aliasing portions occurring in two different domains are matched to each other.

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 domain different from the 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 the same 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 an 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 a 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 different frequency domain,

wherein the second encoding branch comprises a first sub-branch for encoding the audio signal in the other frequency domain, and a second sub-branch for encoding the audio signal in the other 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 controller 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 non-aliasing portion and an additional aliasing portion or an 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 the windowed aliasing portion of an encoded second block of audio data subsequent to a 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 transformer for converting the aliasing portion represented in the second domain into the first domain, wherein the 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 the same operating for a complete encoding block, when a 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. Encoded audio signal comprising an encoded first block of an audio signal and an overlapping encoded second block of the audio signal, the encoded first block of the audio signal comprising an aliasing portion and a further portion, the aliasing portion having been transformed from a first domain to a second domain subsequent to windowing the aliasing portion, and the further portion having been transformed from the first domain into the second domain before windowing the second sub-block, wherein the second sub-block has been transformed into a fourth domain using the same block transform rule, and

wherein the encoded second block has been generated by windowing an overlapping block of audio samples and by transforming a windowed block into a third domain, wherein the encoded second block comprises an aliasing portion corresponding to the aliasing portion of the encoded first block of audio samples.

15. Method of encoding an audio signal, 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 domain different from the 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 the same block transform rule to acquire a converted first block; and

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

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

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

combining the windowed aliasing portion and the windowed aliasing portion of an encoded second block of audio data to acquire a time-domain aliasing cancellation, subsequent to a 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.

17. 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 domain different from the 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 the same block transform rule to acquire a converted first block; and

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

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

combining the windowed aliasing portion and the windowed aliasing portion of an encoded second block of audio data to acquire a time-domain aliasing cancellation, subsequent to a 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.