Audio encoding/decoding with syntax portions using forward aliasing cancellation

• US 9,257,130 B2
• Filed: 01/08/2013
• Issued: 02/09/2016
• Est. Priority Date: 07/08/2010
• 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: Lecomte, Jeremie, Warmbold, Patrick, Bayer, Stefan
• Primary Examiner(s): Lerner, Martin
• Application Number:
  US13/736,762
• Publication Number:
  US 20130124215A1
• Time in Patent Office: 1,127 Days
• Field of Search: 704/205, 704/206, 704/211, 704/219, 704/500, 704/501, 704/204
• US Class Current: 1/1
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• 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

A codec supporting switching between time-domain aliasing cancellation transform coding mode and time-domain coding mode is made less liable to frame loss by adding a further syntax portion to the frames, depending on which the parser of the decoder may select between a first action of expecting the current frame to have, and thus reading forward aliasing cancellation data from the current frame and a second action of not-expecting the current frame to have, and thus not reading forward aliasing cancellation data from the current frame. In other words, while a bit of coding efficiency is lost due to the provision of the new syntax portion, it is merely the new syntax portion which provides for the ability to use the codec in case of a communication channel with frame loss. Without the new syntax portion, the decoder would not be capable of decoding any data stream portion after a loss and will crash in trying to resume parsing. Thus, in an error prone environment, the coding efficiency is prevented from vanishing by the introduction of the new syntax portion.

Claims

1. Decoder apparatus for decoding a data stream comprising a sequence of frames comprising a plurality of respective frames into which time segments of an information signal are coded, respectively, comprising

a parser configured to parse the data stream, wherein the parser is configured to, in parsing the data stream, read a first syntax portion and a second syntax portion from a current frame;

and

a reconstructor configured to reconstruct a current time segment of the information signal associated with the current frame based on information acquired from the current frame by the parsing, using, depending on a first selection, a Time-Domain Aliasing Cancellation transform decoding mode or a time-domain decoding mode, the first selection depending on the first syntax portion,

wherein the parser is configured to, in parsing the data stream, perform a first action of expecting the current frame to comprise, and thus reading forward aliasing cancellation data from the current frame or a second action of not-expecting the current frame to comprise, and thus not reading forward aliasing cancellation data from the current frame, wherein the parser is configured to perform a second selection selecting which of the first action and the second action is performed, depending on the second syntax portion,

wherein the reconstructor is configured to perform forward aliasing cancellation at a boundary between the current time segment and a previous time segment of a previous frame using the forward aliasing cancellation data,

wherein at least one of the parser and the reconstructor is implemented on a microprocessor, a programmable logic device or an electronic circuit.

2. Decoder apparatus according to claim 1, wherein the first and second syntax portions are comprised by each frame, wherein the first syntax portion associates the respective frame from which the first syntax portion has been read, with a first frame type or a second frame type and, if the respective frame is of the second frame type, associates sub frames comprising a plurality of respective sub frames of a division of the respective frame, composed of a number of sub frames, with a respective one of a first sub frame type and a second sub frame type, wherein the reconstructor is configured to, if the first syntax portion associates the respective frame with the first frame type, use frequency domain decoding as a first version of the time-domain aliasing cancellation transform decoding mode to reconstruct the time segment associated with the respective frame, and, if the first syntax portion associates the respective frame with the second frame type, use, for each sub frame of the respective frame, transform coded excitation linear prediction decoding as a second version of the time-domain aliasing cancellation transform decoding mode to reconstruct a sub portion of the time segment of the respective frame, which is associated with the respective sub frame, if the first syntax portion associates the respective sub frame of the respective frame with the first sub frame type, and codebook excitation linear prediction decoding as the time-domain decoding mode to reconstruct a sub portion of the time segment of the respective frame, which is associated with the respective sub frame, if the first syntax portion associates the respective sub frame with the second sub frame type.

3. Decoder apparatus according to claim 2, wherein the reconstructor is configured to

per frame of the first frame type, perform a spectral varying de-quantization of transform coefficient information within the respective frame of the first frame type based on scale factor information within the respective frame of the first frame type, and a re-transform on the de-quantized transform coefficient information to acquire a re-transformed signal segment extending, in time, over and beyond the time segment associated with the respective frame of the first frame type, and

per frame of the second frame type,

per sub frame of the first sub frame type of the respective frame of the second frame type,

derive a spectral weighting filter from LPC information within the respective frame of the second frame type,

spectrally weighting transform coefficient information within the respective sub frame of the first sub frame type using the spectral weighting filter, and

re-transform the spectrally weighted transform coefficient information to acquire a re-transformed signal segment extending, in time, over and beyond the sub portion of the time segment associated with the respective sub frame of the first sub frame type, and,

per sub frame of the second sub frame type of the respective frame of the second frame type,

derive an excitation signal from excitation update information within the respective sub frame of the second sub frame type and

perform LPC synthesis filtering on the excitation signal using the LPC information within the respective frame of the second frame type in order to acquire an LP synthesized signal segment for the sub portion of the time segment associated with the respective sub frame of the second sub frame type, and

perform time-domain aliasing cancellation within temporarily overlapping window portions at boundaries between time segments of immediately consecutive ones of frames of the first frame type and sub portions of time segments, which are associated with sub frames of the first sub frame type, to reconstruct the information signal thereacross, and

if the previous frame is of the first frame type or of the second frame type with the last sub frame thereof being of the first sub frame type, and the current frame is of the second frame type with the first sub frame thereof being of the second sub frame type, derive a first forward aliasing cancellation synthesis signal from the forward aliasing cancellation data and add the first forward aliasing cancellation synthesis signal to the re-transformed signal segment within the previous time segment to reconstruct the information signal across the boundary between the previous and current frames, and

if the previous frame is of the second frame type with the first sub frame thereof being of the second sub frame type, and the current frame is of the first frame type or of the second frame type with the last sub frame thereof being of the first sub frame type, derive a second forward aliasing cancellation synthesis signal from the forward aliasing cancellation data and add the second forward aliasing cancellation synthesis signal to the re-transformed signal segment within the current time segment to reconstruct the information signal across the boundary between the previous and current time segments.

4. Decoder apparatus according to claim 3, wherein the reconstructor is configured to

derive the first forward aliasing cancellation synthesis signal from the forward aliasing cancellation data by performing a re-transform on transform coefficient information comprised by the forward aliasing cancellation data or derive the second forward aliasing cancellation synthesis signal from the forward aliasing cancellation data by performing the re-transform on transform coefficient information comprised by the forward aliasing cancellation data.

5. Decoder apparatus according to claim 3, wherein the second syntax portion comprises a first flag signaling as to whether forward aliasing cancellation data is present or not in the respective frame, and the parser is configured to perform the second selection depending on the first flag, and wherein the second syntax portion further comprises a second flag merely within frames of the second frame type, the second flag signaling as to whether the previous frame is of the first frame type or of the second frame type with the last sub frame thereof being of the first sub frame type.

6. Decoder apparatus according to claim 5, wherein the parser is configured to perform the reading of the forward aliasing cancellation data from the current frame, if the current frame is of the second frame type, depending on the second flag in that a forward aliasing cancellation gain is parsed from the forward aliasing cancellation data in case of the previous frame being of the first frame type, and not if the previous frame being of the second frame type with the last sub frame thereof being of the first sub frame type, wherein the reconstructor is configured to perform the forward aliasing cancellation at an intensity which depends on the forward aliasing cancellation gain in case of the previous frame being of the first frame type.

7. Decoder apparatus according to claim 6, wherein the second syntax portion further comprises a third flag signaling as to whether the previous frame involves a long transform window or short transform windows, merely within frames of the second frame type if the second flag signals that the previous frame is of the first frame type, wherein the parser is configured to perform the reading of the forward aliasing cancellation data from the current frame depending on the third flag such that an amount of forward aliasing cancellation data is greater if the previous frame involves the long transform window, and is lower if the previous frame involves the short transform windows.

8. Decoder apparatus according to claim 3, wherein the reconstructor is configured to, if the previous frame is of the second frame type with the last sub frame thereof being of the second sub frame type and the current frame is of the first frame type or the second frame type with the last sub frame thereof being of the first sub frame type, perform a windowing on the LP synthesis signal segment of the last sub frame of the previous frame to acquire a first aliasing cancellation signal segment and add the first aliasing cancellation signal segment to the re-transformed signal segment within the current time segment.

9. Decoder apparatus according to claim 3, wherein the reconstructor is configured to, if the previous frame is of the second frame type with the last sub frame thereof being of the second sub frame type and the current frame is of the first frame type or the second frame type with a first sub frame thereof being of the first sub frame type, continue the LPC synthesis filtering performed on the excitation signal from the previous frame into the current frame, window a thus derived continuation of the LP synthesis signal segment of the previous frame within the current frame to acquire a second aliasing cancellation signal segment and add the second aliasing cancellation signal segment to the re-transformed signal segment within the current time segment.

10. Decoder apparatus according to claim 1, wherein the second syntax portion comprises a set of possible values each of which is uniquely associated with one of a set of possibilities comprising

the previous frame being of the first frame type,

the previous frame being of the second frame type with the last sub frame thereof being of the first sub frame type, and

the previous frame being of the second frame type with the last sub frame thereof being of the second sub frame type, and

the parser is configured to perform the second selection based on a comparison between the second syntax portion of the current frame and the first syntax portion of the previous frame.

11. Decoder apparatus according to claim 10, wherein the parser is configured to perform the reading of the forward aliasing cancellation data from the current frame, if the current frame is of the second frame type, depending on the previous frame being of the second frame type with the last sub frame thereof being of the first sub frame type or the previous frame being of the first frame type in that a forward aliasing cancellation gain is parsed from the forward aliasing cancellation data in case of the previous frame being of the first frame type, and not if the previous frame being of the second frame type with the last sub frame thereof being of the first sub frame type, wherein the reconstructor is configured to perform the forward aliasing cancellation at an intensity which depends on the forward aliasing cancellation gain in case of the previous frame being of the first frame type.

12. Decoder apparatus according to claim 11, wherein the parser is configured to read, if the current frame is of the first frame type, the forward aliasing cancellation gain from the forward aliasing cancellation data wherein the reconstructor is configured to perform the forward aliasing cancellation at an intensity which depends on the forward aliasing cancellation gain.

13. Decoder apparatus according to claim 1, wherein the second syntax portion comprises a set of possible values each of which is uniquely associated with one of a set of possibilities comprising

the previous frame being of the first frame type with involving a long transform window,

the previous frame being of the first frame type with involving short transform windows,

the previous frame being of the second frame type with the last sub frame thereof being of the first sub frame type, and

the previous frame being of the second frame type with the last sub frame thereof being of the second sub frame type, and

the parser is configured to perform the second selection based on a comparison between the second syntax portion of the current frame and the first syntax portion of the previous frame, and perform the reading of the forward aliasing cancellation data from the current frame, if the previous frame is of the first frame type, depending on the previous frame involving the long transform window or short transform windows such that an amount of forward aliasing cancellation data is greater if the previous frame involves the long transform window, and is lower if the previous frame involves the short transform windows.

14. Decoder apparatus according to claim 1, wherein the parser is configured to, in parsing the data stream, perform the second selection depending on the second syntax portion and independent from as to whether the current frame and the previous frame are decoded using equal or different ones of the Time-Domain Aliasing Cancellation transform decoding mode and the time-domain decoding mode.

15. Encoder apparatus for encoding an information signal into a data stream such that the data stream comprises a sequence of frames into which time segments of the information signal are coded, respectively, comprising

a constructor configured to code a current time segment of the information signal into information of the current frame using, depending on a first selection, a Time-Domain Aliasing Cancellation transform coding mode or a time-domain coding mode;

and

an inserter configured to insert the information into the current frame along with a first syntax portion and a second syntax portion, wherein the first syntax portion signals the first selection,

wherein the constructor and inserter are configured to

determine forward aliasing cancellation data for forward aliasing cancellation at a boundary between the current time segment and a previous time segment of a previous frame and insert the forward aliasing cancellation data into the current frame in case the current frame and the previous frame are encoded using different ones of the Time-Domain Aliasing Cancellation transform coding mode and the time-domain coding mode, and

refraining from inserting any forward aliasing cancellation data into the current frame in case the current frame and the previous frame are encoded using equal ones of the Time-Domain Aliasing Cancellation transform coding mode and the time-domain coding mode,

wherein the second syntax portion is set depending on as to whether the current frame and the previous frame are encoded using equal or different ones of the Time-Domain Aliasing Cancellation transform coding mode and the time-domain coding mode,

wherein at least one of the constructor and the inserter is implemented on a microprocessor, a programmable logic device or an electronic circuit.

16. Encoder apparatus according to claim 15, wherein the encoder apparatus is configured to,

if the current frame and the previous frame are encoded using equal ones of the Time-Domain Aliasing Cancellation transform coding mode and the time-domain coding mode, set the second syntax portion to a first state signalling the absence of the forward aliasing cancellation data in the current frame, and,

if the current frame and the previous frame are encoded using different ones of the Time-Domain Aliasing Cancellation transform coding mode and the time-domain coding mode, decide in a rate/distortion optimization sense, so as to

refrain from inserting the forward aliasing cancellation data into the current frame although the current frame and the previous frame are encoded using different ones of the time-domain aliasing cancellation transform coding mode and the time-domain coding mode, with setting the second syntax portion such that the second syntax portion signals the absence of the forward aliasing cancellation data in the current frame, or

inserting the forward aliasing cancellation data into the current frame with setting the second syntax portion such that the second syntax portion signals the insertion of the forward aliasing cancellation data into the current frame.

17. Method for decoding a data stream comprising a sequence of frames into which time segments of an information signal are coded, respectively, comprising

parsing the data stream, wherein parsing the data stream comprises reading a first syntax portion and a second syntax portion from a current frame;

and

reconstructing a current time segment of the information signal associated with the current frame based on information acquired from the current frame by the parsing, using, depending on a first selection, a Time-Domain Aliasing Cancellation transform decoding mode or a time-domain decoding mode, the first selection depending on the first syntax portion,

wherein, in parsing the data stream, a first action of expecting the current frame to comprise, and thus reading forward aliasing cancellation data from the current frame or a second action of not-expecting the current frame to comprise, and thus not reading forward aliasing cancellation data from the current frame is performed, wherein a second selection as to which the first and second action is performed, is performed depending on the second syntax portion,

wherein the reconstructing comprises performing forward aliasing cancellation at a boundary between the current time segment and a previous time segment of a previous frame using the forward aliasing cancellation data,

wherein at least one of the parsing and the reconstructing is performed using a microprocessor, a programmable logic device or an electronic circuit.

18. Method for encoding an information signal into data stream such that the data stream comprises a sequence of frames into which time segments of the information signal are coded, respectively, comprising

coding a current time segment of the information signal into information of the current frame using, depending on a first selection, a Time-Domain Aliasing Cancellation transform encoding mode or a time-domain encoding mode;

and

inserting the information into the current frame along with a first syntax portion and a second syntax portion, wherein the first syntax portion signals the first selection,

determining forward aliasing cancellation data for forward aliasing cancellation at a boundary between the current time segment and a previous time segment of a previous frame and inserting the forward aliasing cancellation data into the current frame in case the current frame and the previous frame are encoded using different ones of the Time-Domain Aliasing Cancellation transform encoding mode and the time-domain encoding mode, and refraining from inserting any forward aliasing cancellation data into the current frame in case the current frame and the previous frame are encoded using equal ones of the Time-Domain Aliasing Cancellation transform encoding mode and the time-domain encoding mode,

wherein the second syntax portion is set depending on as to whether the current frame and the previous frame are encoded using equal or different ones of the Time-Domain Aliasing Cancellation transform encoding mode and the time-domain encoding mode,

wherein at least one of the coding and the inserting is performed using a microprocessor, a programmable logic device or an electronic circuit.

19. A non-transitory computer-readable medium having stored thereon a computer program comprising a program code for performing, when running on a computer, a method for decoding a data stream comprising a sequence of frames into which time segments of an information signal are coded, respectively, comprising

parsing the data stream, wherein parsing the data stream comprises reading a first syntax portion and a second syntax portion from a current frame;

and

reconstructing a current time segment of the information signal associated with the current frame based on information acquired from the current frame by the parsing, using, depending on a first selection, a Time-Domain Aliasing Cancellation transform decoding mode or a time-domain decoding mode, the first selection depending on the first syntax portion,

wherein, in parsing the data stream, a first action of expecting the current frame to comprise, and thus reading forward aliasing cancellation data from the current frame and a second action of not-expecting the current frame to comprise, and thus not reading forward aliasing cancellation data from the current frame is performed, wherein a second selection as to which of the first and second action is performed, is performed depending on the second syntax portion,

wherein the reconstructing comprises performing forward aliasing cancellation at a boundary between the current time segment and a previous time segment of a previous frame using the forward aliasing cancellation data.

20. A non-transitory computer-readable medium having stored thereon a computer program comprising a program code for performing, when running on a computer, a method for encoding an information signal into a data stream such that the data stream comprises a sequence of frames into which time segments of the information signal are coded, respectively, comprising

coding a current time segment of the information signal into information of a current frame using, depending on a first selection, a Time-Domain Aliasing Cancellation transform encoding mode or a time-domain encoding mode;

and

inserting the information into the current frame along with a first syntax portion and a second syntax portion, wherein the first syntax portion signals the first selection,

determining forward aliasing cancellation data for forward aliasing cancellation at a boundary between the current time segment and a previous time segment of a previous frame and inserting the forward aliasing cancellation data into the current frame in case the current frame and the previous frame are encoded using different ones of the Time-Domain Aliasing Cancellation transform encoding mode and the time-domain encoding mode, and refraining from inserting any forward aliasing cancellation data into the current frame in case the current frame and the previous frame are encoded using equal ones of the Time-Domain Aliasing Cancellation transform encoding mode and the time-domain encoding mode,

wherein the second syntax portion is set depending on as to whether the current frame and the previous frame are encoded using equal or different ones of the Time-Domain Aliasing Cancellation transform encoding mode and the time-domain encoding mode.