Low-complexity encoding/decoding of quantized MDCT spectrum in scalable speech and audio codecs

• US 20090234644A1
• Filed: 10/21/2008
• Published: 09/17/2009
• Est. Priority Date: 10/22/2007
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Reznik, Yuriy, Huang, Pengjun
• Granted Patent: US 8,527,265 B2
• Time in Patent Office: Days
• US Class Current: 704/203
• CPC Class Codes: G10L 19/038 Vector quantisation, e.g. TwinVQ audio
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding

Abstract

A scalable speech and audio codec is provided that implements combinatorial spectrum encoding. A residual signal is obtained from a Code Excited Linear Prediction (CELP)-based encoding layer, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal. The residual signal is transformed at a Discrete Cosine Transform (DCT)-type transform layer to obtain a corresponding transform spectrum having a plurality of spectral lines. The transform spectrum spectral lines are transformed using a combinatorial position coding technique.

The combinatorial position coding technique includes generating a lexicographical index for a selected subset of spectral lines, where each lexicographic index represents one of a plurality of possible binary strings representing the positions of the selected subset of spectral lines. The lexicographical index represents non-zero spectral lines in a binary string in fewer bits than the length of the binary string.

Claims

1. A method for encoding in a scalable speech and audio codec, comprising:

obtaining a residual signal from a Code Excited Linear Prediction (CELP)-based encoding layer, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal;

transforming the residual signal at a Discrete Cosine Transform (DCT)-type transform layer to obtain a corresponding transform spectrum having a plurality of spectral lines; and

encoding the transform spectrum spectral lines using a combinatorial position coding technique.

2. The method of claim 1, wherein the DCT-type transform layer is a Modified Discrete Cosine Transform (MDCT) layer and the transform spectrum is an MDCT spectrum.

3. The method of claim 1, wherein encoding of the transform spectrum spectral lines includes:

encoding positions of a selected subset of spectral lines based on representing spectral line positions using the combinatorial position coding technique for non-zero spectral lines positions.

4. The method of claim 1, further comprising:

splitting the plurality of spectral lines into a plurality of sub-bands; and

grouping consecutive sub-bands into regions.

5. The method of claim 4, further comprising:

encoding a main pulse selected from a plurality of spectral lines for each of the sub-bands in the region.

6. The method of claim 4, further comprising:

encoding positions of a selected subset of spectral lines within a region based on representing spectral line positions using the combinatorial position coding technique for non-zero spectral lines positions;

wherein encoding of the transform spectrum spectral lines includes generating an array, based on the positions of the selected subset of spectral lines, of all possible binary strings of length equal to all positions in the region.

7. The method of claim 4, wherein the regions are overlapping and each region includes a plurality of consecutive sub-bands.

8. The method of claim 1, wherein the combinatorial position coding technique includes:

generating a lexicographical index for a selected subset of spectral lines, where each lexicographic index represents one of a plurality of possible binary strings representing the positions of the selected subset of spectral lines.

9. The method of claim 8, wherein the lexicographical index represents non-zero spectral lines in a binary string in fewer bits than the length of the binary string.

10. The method of claim 1, wherein the combinatorial position coding technique includes:

generating an index representative of positions of spectral lines within a binary string, the positions of the spectral lines being encoded based a combinatorial formula;

$\begin{array}{c}\mathrm{index}<br><br>\left(n,k,w\right)=<br><br>i<br><br>\left(w\right)\\ =<br><br>\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>w_j<br><br>\left(\begin{array}{c}n-j\\ \underset{i=j}{\overset{n}{\sum <br><br>}}<br><br>w_i\end{array}\right)\end{array}$

where n is the length of the binary string, k is the number of selected spectral lines to be encoded, and w_j represents individual bits of the binary string.

11. The method of claim 1, further comprising:

dropping a set of spectral lines to reduce the number of spectral lines prior to encoding.

12. The method of claim 1, wherein the reconstructed version of the original audio signal is obtained by:

synthesizing an encoded version of the original audio signal from the CELP-based encoding layer to obtain a synthesized signal;

re-emphasizing the synthesized signal; and

up-sampling the re-emphasized signal to obtain the reconstructed version of the original audio signal.

13. A scalable speech and audio encoder device, comprising:

a Discrete Cosine Transform (DCT)-type transform layer module adapted to

obtain a residual signal from a Code Excited Linear Prediction (CELP)-based encoding layer module, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal; and

transform the residual signal at to obtain a corresponding transform spectrum having a plurality of spectral lines; and

a combinatorial spectrum encoder adapted to encode the transform spectrum spectral lines using a combinatorial position coding technique.

14. The device of claim 13, wherein the DCT-type transform layer module is a Modified Discrete Cosine Transform (MDCT) layer module and the transform spectrum is an MDCT spectrum.

15. The device of claim 13, wherein encoding of the transform spectrum spectral lines includes:

encoding positions of a selected subset of spectral lines based on representing spectral line positions using the combinatorial position coding technique for non-zero spectral lines positions.

16. The device of claim 13, further comprising:

a sub-band generator adapted to split the plurality of spectral lines into a plurality of sub-bands; and

a region generator adapted to group consecutive sub-bands into regions.

17. The device of claim 16, further comprising:

a main pulse encoder adapted to encode a main pulse selected from a plurality of spectral lines for each of the sub-bands in the region.

18. The method of claim 16, further comprising:

a sub-pulse encoder adapted to encode positions of a selected subset of spectral lines within a region based on representing spectral line positions using the combinatorial position coding technique for non-zero spectral lines positions;

wherein encoding of the transform spectrum spectral lines includes generating an array, based on the positions of the selected subset of spectral lines, of all possible binary strings of length equal to all positions in the region.

19. The device of claim 16, wherein the regions are overlapping and each region includes a plurality of consecutive sub-bands.

20. The device of claim 13, wherein the combinatorial position coding technique includes:

generating a lexicographical index for a selected subset of spectral lines, where each lexicographic index represents one of a plurality of possible binary strings representing the positions of the selected subset of spectral lines.

21. The device of claim 20, wherein the lexicographical index represents non-zero spectral lines in a binary string in fewer bits than the length of the binary string.

22. The device of claim 13, wherein the combinatorial spectrum encoder is adapted to generate an index representative of positions of spectral lines within a binary string, the positions of the spectral lines being encoded based a combinatorial formula:

$\begin{array}{c}\mathrm{index}<br><br>\left(n,k,w\right)=<br><br>i<br><br>\left(w\right)\\ =<br><br>\underset{j=1}{\overset{n}{\sum <br><br>}}<br><br>w_j<br><br>\left(\begin{array}{c}n-j\\ \underset{i=j}{\overset{n}{\sum <br><br>}}<br><br>w_i\end{array}\right)\end{array}$

where n is the length of the binary string, k is the number of selected spectral lines to be encoded, and w_j represents individual bits of the binary string.

23. The device of claim 13, wherein the reconstructed version of the original audio signal is obtained by:

synthesizing an encoded version of the original audio signal from the CELP-based encoding layer to obtain a synthesized signal;

re-emphasizing the synthesized signal; and

up-sampling the re-emphasized signal to obtain the reconstructed version of the original audio signal.

24. A scalable speech and audio encoder device, comprising:

means for obtaining a residual signal from a Code Excited Linear Prediction (CELP)-based encoding layer, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal;

means for transforming the residual signal at a Discrete Cosine Transform (DCT)-type transform layer to obtain a corresponding transform spectrum having a plurality of spectral lines; and

means for encoding the transform spectrum spectral lines using a combinatorial position coding technique.

25. A processor including a scalable speech and audio encoding circuit adapted to:

obtain a residual signal from a Code Excited Linear Prediction (CELP)-based encoding layer, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal;

transform the residual signal at a Discrete Cosine Transform (DCT)-type transform layer to obtain a corresponding transform spectrum having a plurality of spectral lines; and

encode the transform spectrum spectral lines using a combinatorial position coding technique.

26. A machine-readable medium comprising instructions operational for scalable speech and audio encoding, which when executed by one or more processors causes the processors to:

obtain a residual signal from a Code Excited Linear Prediction (CELP)-based encoding layer, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal;

transform the residual signal at a Discrete Cosine Transform (DCT)-type transform layer to obtain a corresponding transform spectrum having a plurality of spectral lines; and

encode the transform spectrum spectral lines using a combinatorial position coding technique.

27. A method for scalable speech and audio decoding, comprising:

obtaining an index representing a plurality of transform spectrum spectral lines of a residual signal, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal from a Code Excited Linear Prediction (CELP)-based encoding layer;

decoding the index by reversing a combinatorial position coding technique used to encode the plurality of transform spectrum spectral lines; and

synthesizing a version of the residual signal using the decoded plurality of transform spectrum spectral lines at an Inverse Discrete Cosine Transform (IDCT)-type inverse transform layer.

28. The method of claim 27, further comprising:

receiving a CELP-encoded signal encoding the original audio signal;

decoding a CELP-encoded signal to generate a decoded signal; and

combining the decoded signal with the synthesized version of the residual signal to obtain a reconstructed version of the original audio signal.

29. The method of claim 27, wherein synthesizing a version of the residual signal includes

applying an inverse DCT-type transform to the transform spectrum spectral lines to produce a time-domain version of the residual signal.

30. The method of claim 27, wherein decoding of the transform spectrum spectral lines includes:

decoding positions of a selected subset of spectral lines based on representing spectral line positions using the combinatorial position coding technique for non-zero spectral lines positions.

31. The method of claim 27, wherein the index represents non-zero spectral lines in a binary string in fewer bits than the length of the binary string.

32. The method of claim 27, wherein the DCT-type inverse transform layer is an Inverse Modified Discrete Cosine Transform (IMDCT) layer and the transform spectrum is an MDCT spectrum.

33. The method of claim 27, wherein the obtained index represents positions of spectral lines within a binary string, the positions of the spectral lines being encoded based a combinatorial formula:

$\begin{array}{c}\mathrm{index}<br><br>\left(n,k,w\right)=<br><br>i<br><br>\left(w\right)\\ =<br><br>\underset{j=1}{\overset{n}{\sum <br><br>}}<br><br>w_j<br><br>\left(\begin{array}{c}n-j\\ \underset{i=j}{\overset{n}{\sum <br><br>}}<br><br>w_i\end{array}\right)\end{array}$

where n is the length of the binary string, k is the number of selected spectral lines to be encoded, and w_j represents individual bits of the binary string.

34. A scalable speech and audio decoder device, comprising:

a combinatorial spectrum decoder adapted to

obtain an index representing a plurality of transform spectrum spectral lines of a residual signal, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal from a Code Excited Linear Prediction (CELP)-based encoding layer;

decode the index by reversing a combinatorial position coding technique used to encode the plurality of transform spectrum spectral lines; and

an Inverse Discrete Cosine Transform (IDCT)-type inverse transform layer module adapted to synthesize a version of the residual signal using the decoded plurality of transform spectrum spectral lines.

35. The device of claim 34, further comprising:

a CELP decoder adapted to

receive a CELP-encoded signal encoding the original audio signal;

decode a CELP-encoded signal to generate a decoded signal; and

combine the decoded signal with the synthesized version of the residual signal to obtain a reconstructed version of the original audio signal.

36. The device of claim 34, wherein synthesizing a version of the residual signal, the (IDCT)-type inverse transform layer module is adapted to apply an inverse DCT-type transform to the transform spectrum spectral lines to produce a time-domain version of the residual signal.

37. The device of claim 34, wherein the index represents non-zero spectral lines in a binary string in fewer bits than the length of the binary string.

38. A scalable speech and audio decoder device, comprising:

means for obtaining an index representing a plurality of transform spectrum spectral lines of a residual signal, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal from a Code Excited Linear Prediction (CELP)-based encoding layer;

means for decoding the index by reversing a combinatorial position coding technique used to encode the plurality of transform spectrum spectral lines; and

means for synthesizing a version of the residual signal using the decoded plurality of transform spectrum spectral lines at an Inverse Discrete Cosine Transform (IDCT)-type inverse transform layer.

39. A processor including a scalable speech and audio decoding circuit adapted to:

obtain an index representing a plurality of transform spectrum spectral lines of a residual signal, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal from a Code Excited Linear Prediction (CELP)-based encoding layer;

decode the index by reversing a combinatorial position coding technique used to encode the plurality of transform spectrum spectral lines; and

synthesize a version of the residual signal using the decoded plurality of transform spectrum spectral lines at an Inverse Discrete Cosine Transform (IDCT)-type inverse transform layer.

40. A machine-readable medium comprising instructions operational for scalable speech and audio decoding, which when executed by one or more processors causes the processors to:

obtain an index representing a plurality of transform spectrum spectral lines of a residual signal, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal from a Code Excited Linear Prediction (CELP)-based encoding layer;

decode the index by reversing a combinatorial position coding technique used to encode the plurality of transform spectrum spectral lines; and

synthesize a version of the residual signal using the decoded plurality of transform spectrum spectral lines at an Inverse Discrete Cosine Transform (IDCT)-type inverse transform layer.