Systems, methods, apparatus, and computer-readable media for coding of harmonic signals

• US 8,924,222 B2
• Filed: 07/28/2011
• Issued: 12/30/2014
• Est. Priority Date: 07/30/2010
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Rajendran, Vivek, Duni, Ethan Robert, Krishnan, Venkatesh, Tawari, Ashish Kumar
• Primary Examiner(s): ALBERTALLI, BRIAN LOUIS
• Application Number:
  US13/192,956
• Publication Number:
  US 20120029923A1
• Time in Patent Office: 1,251 Days
• Field of Search: None
• US Class Current: 704/501
• CPC Class Codes: G10L 19/038 Vector quantisation, e.g. TwinVQ audio
• CPC Class Codes: G10L 19/093 using sinusoidal excitation models
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals

Abstract

A scheme for coding a set of transform coefficients that represent an audio-frequency range of a signal uses a harmonic model to parameterize a relationship between the locations of regions of significant energy in the frequency domain.

Claims

1. A method of audio signal processing, said method comprising:

in a frequency domain, locating a plurality of peaks in a reference audio signal;

selecting a number Nf of candidates for a fundamental frequency of a harmonic model, each based on the location of a corresponding one of the plurality of peaks in the frequency domain;

based on the locations of at least two of the plurality of peaks in the frequency domain, calculating by a communications device a number Nd of candidates for a spacing between harmonics of the harmonic model;

for each of a plurality of different pairs of the fundamental frequency and harmonic spacing candidates, selecting by the communications device a set of at least one subband of a target audio signal, wherein a location in the frequency domain of each subband in the set is based on the pair of candidates;

for each of the plurality of different pairs of candidates, calculating an energy value from the corresponding set of at least one subband of the target audio signal; and

based on at least a plurality of the calculated energy values, selecting a pair of candidates from among the plurality of different pairs of candidates,

wherein at least one among the numbers Nf and Nd has a value greater than one.

2. The method according to claim 1, wherein said target audio signal is the reference audio signal.

3. The method according to claim 1, wherein said reference audio signal represents a first frequency range of an audio signal, and

wherein said target audio signal represents a second frequency range of the audio signal that is different than the first frequency range.

4. The method according to claim 3, wherein said method includes mapping the number Nf of fundamental frequency candidates into the second frequency range.

5. The method according to claim 1, wherein said method includes performing a gain shape vector quantization operation on the set of at least one subband indicated by the selected pair of candidates.

6. The method according to claim 1, wherein said selecting at least one subband comprises selecting a set of subbands, and

wherein said calculating an energy value from the corresponding set of subbands includes calculating an average energy per subband.

7. The method according to claim 1, wherein said calculating an energy value from the corresponding set of subbands includes calculating a total energy captured by the set of at least one subband.

8. The method according to claim 1, wherein said target audio signal is based on a linear prediction coding residual.

9. The method according to claim 1, wherein said target audio signal is a plurality of modified discrete cosine transform coefficients.

10. The method according to claim 1, wherein said selecting a set of at least one subband includes, for each of at least one of the set of at least one subband, finding a location for the subband, within a specified range of a reference location, at which the energy captured by the subband is maximum, wherein the reference location is based on the candidate pair.

11. The method according to claim 1, wherein said selecting a set of at least one subband includes, for each of at least one of the set of at least one subband, finding a location for the subband, within a specified range of a reference location, at which the sample having the maximum value within the subband is centered within the subband, wherein the reference location is based on the candidate pair.

12. The method according to claim 1, wherein, for at least one of the plurality of different pairs of candidates, said selecting a set of at least one subband includes, for each of at least one of the at least one subband:

based on the candidate pair, calculating a first location for the subband such that the subband excludes a specified one of the located peaks, wherein the first location is on one side of the specified located peak on a frequency-domain axis;

based on the candidate pair, calculating a second location for the subband such that the subband excludes the specified located peak, wherein the second location is on the other side of the specified located peak on the frequency-domain axis;

identifying the one among the first and second locations at which the subband has the lowest energy.

13. The method according to claim 1, wherein said method comprises producing an encoded signal that indicates the values of the selected pair of candidates and the contents of each subband of the corresponding selected set of at least one subband.

14. The method according to claim 1, wherein said selecting at least one subband comprises selecting a set of subbands, and

wherein said method comprises:

quantizing the selected set of subbands that corresponds to the selected pair of candidates;

dequantizing the quantized set of subbands to obtain a dequantized set of subbands; and

constructing a decoded signal by placing the dequantized subbands at corresponding locations that are based on the selected pair of candidates,

wherein the locations of the dequantized subbands within the decoded signal differ from the locations, within the target audio signal, of the corresponding subbands of the selected set that corresponds to the selected pair of candidates.

15. A method of constructing a decoded audio frame, said method comprising:

placing by a communications device a first one of a plurality of decoded subband vectors according to a fundamental frequency value;

placing by the communications device the rest of the plurality of decoded subband vectors according to the fundamental frequency value and a harmonic spacing value; and

inserting a decoded residual signal at locations of the frame that are not occupied by the plurality of decoded subband vectors.

16. The method according to claim 15, wherein, for each adjacent pair of the plurality of decoded subband vectors, a distance between the centers of the vectors is equal to the harmonic spacing value.

17. The method according to claim 15, wherein said method comprises erasing portions of the decoded residual signal that correspond to possible locations of the plurality of decoded subband vectors.

18. The method according to claim 15, wherein said inserting a decoded residual signal includes inserting values of the decoded residual signal, in order from a first value of the decoded residual signal to a last value of the decoded residual signal, at the unoccupied locations of the frame in order of increasing frequency.

19. The method according to claim 15, wherein said inserting a decoded residual signal includes warping a portion of the decoded residual signal with respect to a frequency-domain axis to fit between adjacent ones among the plurality of decoded subband vectors.

20. An apparatus for audio signal processing, said apparatus comprising:

means for locating a plurality of peaks in a reference audio signal in a frequency domain;

means for selecting a number Nf of candidates for a fundamental frequency of a harmonic model, each based on the location of a corresponding one of the plurality of peaks in the frequency domain;

means for calculating a number Nd of candidates for a spacing between harmonics of the harmonic model, based on the locations of at least two of the plurality of peaks in the frequency domain;

means for selecting, for each of a plurality of different pairs of the fundamental frequency and harmonic spacing candidates, a set of at least one subband of a target audio signal, wherein a location in the frequency domain of each subband in the set is based on the pair of candidates; and

means for calculating, for each of the plurality of different pairs of candidates, an energy value from the corresponding set of at least one subband of the target audio signal; and

means for selecting a pair of candidates from among the plurality of different pairs of candidates, based on at least a plurality of the calculated energy values,

wherein at least one among the numbers Nf and Nd has a value greater than one.

21. The apparatus according to claim 20, wherein said target audio signal is the reference audio signal.

22. The apparatus according to claim 20, wherein said reference audio signal represents a first frequency range of an audio signal, and

wherein said target audio signal represents a second frequency range of the audio signal that is different than the first frequency range.

23. The apparatus according to claim 22, wherein said apparatus includes means for mapping the number Nf of fundamental frequency candidates into the second frequency range.

24. The apparatus according to claim 20, wherein said apparatus includes means for performing a gain shape vector quantization operation on the set of at least one subband indicated by the selected pair of candidates.

25. The apparatus according to claim 20, wherein said means for selecting a set of at least one subband is configured to select, for each of the plurality of different pairs of candidates, a set of subbands, and

wherein said means for calculating an energy value from the corresponding set of subbands includes means for calculating an average energy per subband.

26. The apparatus according to claim 20, wherein said means for calculating an energy value from the corresponding set of subbands includes means for calculating a total energy captured by the set of at least one subband.

27. The apparatus according to claim 20, wherein said target audio signal is based on a linear prediction coding residual.

28. The apparatus according to claim 20, wherein said target audio signal is a plurality of modified discrete cosine transform coefficients.

29. The apparatus according to claim 20, wherein said means for selecting a set of at least one subband includes means for finding, for each of at least one of the set of at least one subband, a location for the subband, within a specified range of a reference location, at which the energy captured by the subband is maximum, wherein the reference location is based on the candidate pair.

30. The apparatus according to claim 20, wherein said means for selecting a set of at least one subband includes means for finding, for each of at least one of the set of at least one subband, a location for the subband, within a specified range of a reference location, at which the sample having the maximum value within the subband is centered within the subband, wherein the reference location is based on the candidate pair.

31. The apparatus according to claim 20, wherein, for at least one of the plurality of different pairs of candidates, said means for selecting a set of at least one subband includes:

means for calculating, for each of at least one of the at least one subband and based on the candidate pair, (A) a first location for the subband such that the subband excludes a specified one of the located peaks, wherein the first location is on one side of the specified located peak on a frequency-domain axis, and (B) a second location for the subband such that the subband excludes the specified located peak, wherein the second location is on the other side of the specified located peak on the frequency-domain axis; and

means for identifying, for each of said at least one of the at least one subband, the one among the first and second locations at which the subband has the lowest energy.

32. The apparatus according to claim 20, wherein said apparatus comprises means for producing an encoded signal that indicates the values of the selected pair of candidates and the contents of each subband of the corresponding selected set of at least one subband.

33. The apparatus according to claim 20, wherein said means for selecting a set of at least one subband is configured to select, for each of the plurality of different pairs of candidates, a set of subbands, and

wherein said apparatus comprises:

means for quantizing the selected set of subbands that corresponds to the selected pair of candidates;

means for dequantizing the quantized set of subbands to obtain a dequantized set of subbands; and

means for constructing a decoded signal by placing the dequantized subbands at corresponding locations that are based on the selected pair of candidates,

wherein the locations of the dequantized subbands within the decoded signal differ from the locations, within the target audio signal, of the corresponding subbands of the selected set that corresponds to the selected pair of candidates.

34. An apparatus for audio signal processing, said apparatus comprising:

a frequency-domain peak locator configured to locate a plurality of peaks in a reference audio signal in a frequency domain, wherein the frequency-domain peak locator is implemented by the apparatus, and wherein the apparatus comprises hardware;

a fundamental-frequency candidate selector configured to select a number Nf of candidates for a fundamental frequency of a harmonic model, each based on the location of a corresponding one of the plurality of peaks in the frequency domain;

a distance calculator configured to calculate a number Nd of candidates for a spacing between harmonics of the harmonic model, based on the locations of at least two of the plurality of peaks in the frequency domain;

a subband placement selector configured to select, for each of a plurality of different pairs of the fundamental frequency and harmonic spacing candidates, a set of at least one subband of a target audio signal, wherein a location in the frequency domain of each subband in the set is based on the pair of candidates;

an energy calculator configured to calculate, for each of the plurality of different pairs of candidates, an energy value from the corresponding set of at least one subband of the target audio signal; and

a candidate pair selector configured to select a pair of candidates from among the plurality of different pairs of candidates, based on at least a plurality of the calculated energy values,

wherein at least one among the numbers Nf and Nd has a value greater than one.

35. The apparatus according to claim 34, wherein said target audio signal is the reference audio signal.

36. The apparatus according to claim 34, wherein said reference audio signal represents a first frequency range of an audio signal, and

wherein said target audio signal represents a second frequency range of the audio signal that is different than the first frequency range.

37. The apparatus according to claim 36, wherein said subband placement selector is configured to map the number Nf of fundamental frequency candidates into the second frequency range.

38. The apparatus according to claim 34, wherein said apparatus includes a quantizer configured to perform a gain shape vector quantization operation on the set of at least one subband indicated by the selected pair of candidates.

39. The apparatus according to claim 34, wherein said subband placement selector is configured to select, for each of the plurality of different pairs of candidates, a set of subbands, and

wherein said energy calculator is configured to calculate, for each of the plurality of different pairs of candidates, an average energy per subband.

40. The apparatus according to claim 34, wherein said energy calculator is configured to calculate, for each of the plurality of different pairs of candidates, a total energy captured by the set of at least one subband.

41. The apparatus according to claim 34, wherein said target audio signal is based on a linear prediction coding residual.

42. The apparatus according to claim 34, wherein said target audio signal is a plurality of modified discrete cosine transform coefficients.

43. The apparatus according to claim 34, wherein said subband placement selector is configured to find, for each of at least one of the set of at least one subband, a location for the subband, within a specified range of a reference location, at which the energy captured by the subband is maximum, wherein the reference location is based on the candidate pair.

44. The apparatus according to claim 34, wherein said subband placement selector is configured to find, for each of at least one of the set of at least one subband, a location for the subband, within a specified range of a reference location, at which the sample having the maximum value within the subband is centered within the subband, wherein the reference location is based on the candidate pair.

45. The apparatus according to claim 34, wherein, for at least one of the plurality of different pairs of candidates, said subband placement selector is configured to:

calculate, for each of at least one of the at least one subband and based on the candidate pair, (A) a first location for the subband such that the subband excludes a specified one of the located peaks, wherein the first location is on one side of the specified located peak on a frequency-domain axis, and (B) a second location for the subband such that the subband excludes the specified located peak, wherein the second location is on the other side of the specified located peak on the frequency-domain axis; and

identify, for each of said at least one of the at least one subband, the one among the first and second locations at which the subband has the lowest energy.

46. The apparatus according to claim 34, wherein said apparatus comprises a bit packer configured to produce an encoded signal that indicates the values of the selected pair of candidates and the contents of each subband of the corresponding selected set of at least one subband.

47. The apparatus according to claim 34, wherein said subband placement selector is configured to select, for each of the plurality of different pairs of candidates, a set of subbands, and

wherein said apparatus comprises:

a quantizer configured to quantize the selected set of subbands that corresponds to the selected pair of candidates;

a dequantizer configured to dequantize the quantized set of subbands to obtain a dequantized set of subbands; and

subband placement logic configured to construct a decoded signal by placing the dequantized subbands at corresponding locations that are based on the selected pair of candidates,

wherein the locations of the dequantized subbands within the decoded signal differ from the locations, within the target audio signal, of the corresponding subbands of the selected set that corresponds to the selected pair of candidates.

48. A non-transitory computer-readable storage medium having tangible features that when read by a machine cause the machine to:

locate, in a frequency domain, a plurality of peaks in a reference audio signal;

select a number Nf of candidates for a fundamental frequency of a harmonic model, each based on the location of a corresponding one of the plurality of peaks in the frequency domain;

based on the locations of at least two of the plurality of peaks in the frequency domain, calculate a number Nd of candidates for a spacing between harmonics of the harmonic model;

for each of a plurality of different pairs of the fundamental frequency and harmonic spacing candidates, select a set of at least one subband of a target audio signal, wherein a location in the frequency domain of each subband in the set is based on the pair of candidates;

for each of the plurality of different pairs of candidates, calculate an energy value from the corresponding set of at least one subband of the target audio signal; and

based on at least a plurality of the calculated energy values, select a pair of candidates from among the plurality of different pairs of candidates,

wherein at least one among the numbers Nf and Nd has a value greater than one.

49. An apparatus for constructing a decoded audio frame, said apparatus comprising:

a subband placer configured to place a first one of a plurality of decoded subband vectors according to a fundamental frequency value, to place the rest of the plurality of decoded subband vectors according to the fundamental frequency value and a harmonic spacing value, and to insert a decoded residual signal at locations of the frame that are not occupied by the plurality of decoded subband vectors.

50. The apparatus according to claim 49, wherein, for each adjacent pair of the plurality of decoded subband vectors, a distance between the centers of the vectors is equal to the harmonic spacing value.

51. The apparatus according to claim 49, wherein said subband placer is further configured to erase portions of the decoded residual signal that correspond to possible locations of the plurality of decoded subband vectors.

52. The apparatus according to claim 49, wherein said inserting a decoded residual signal includes inserting values of the decoded residual signal, in order from a first value of the decoded residual signal to a last value of the decoded residual signal, at the unoccupied locations of the frame in order of increasing frequency.

53. The apparatus according to claim 49, wherein said inserting a decoded residual signal includes warping a portion of the decoded residual signal with respect to a frequency-domain axis to fit between adjacent ones among the plurality of decoded subband vectors.

54. An apparatus for constructing a decoded audio frame, said apparatus comprising:

means for placing a first one of a plurality of decoded subband vectors according to a fundamental frequency value;

means for placing the rest of the plurality of decoded subband vectors according to the fundamental frequency value and a harmonic spacing value; and

means for inserting a decoded residual signal at locations of the frame that are not occupied by the plurality of decoded subband vectors.

55. The apparatus according to claim 54, wherein, for each adjacent pair of the plurality of decoded subband vectors, a distance between the centers of the vectors is equal to the harmonic spacing value.

56. The apparatus according to claim 54, wherein said apparatus further comprises means for erasing portions of the decoded residual signal that correspond to possible locations of the plurality of decoded subband vectors.

57. The apparatus according to claim 54, wherein said inserting a decoded residual signal includes inserting values of the decoded residual signal, in order from a first value of the decoded residual signal to a last value of the decoded residual signal, at the unoccupied locations of the frame in order of increasing frequency.

58. The apparatus according to claim 54, wherein said inserting a decoded residual signal includes warping a portion of the decoded residual signal with respect to a frequency-domain axis to fit between adjacent ones among the plurality of decoded subband vectors.