Compensation of transient effects in transform coding

• US 7,386,445 B2
• Filed: 01/18/2005
• Issued: 06/10/2008
• Est. Priority Date: 01/18/2005
• Status: Active Grant

• Current Assignee: Conversant Wireless Licensing S.à.r.l. (f/k/a Core Wireless Licensing S.a.r.l.) (MOSAID Technologies Inc. (f/k/a Conversant Intellectual Property Management))
• Original Assignee: Nokia Corporation
• Inventors: Ojala, Pasi
• Primary Examiner(s): MCFADDEN, SUSAN IRIS
• Application Number:
  US11/039,391
• Publication Number:
  US 20060161427A1
• Time in Patent Office: 1,239 Days
• Field of Search: 704/219, 704/203
• US Class Current: 704/219
• CPC Class Codes: G10L 19/025 Detection of transients or attacks for time/frequency resolution switching
• 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

The present invention provides a method for compensating transient effects in transform coding and decoding of a combined speech and audio in electronic devices by using a transform based time-frequency domain codec. The method can combine, e.g., a CELP (code excited linear prediction) type speech codec and a transform type audio codec. The invention describes a compensation method to handle the transient (e.g., from the CELP coding to the transform coding) in transform coding when the number of quantized transform coding coefficients is lower than in the output of the transform.

Claims

1. A method for encoding an acoustic signal, comprising:

encoding a first frame of the acoustic signal using a first encoding method; and

encoding a transient frame of the acoustic signal which follows said first frame and contains M samples using a second encoding method for producing a set of M+K encoding values, wherein M and K are pre-selected integers of at least a value of one.

2. The method of claim 1, wherein a decision for using said first encoding method or said second encoding method is made based on a pre-selected criterion.

3. The method of claim 1, wherein said first encoding method is a time domain codec, or a code excited linear prediction.

4. The method of claim 1, wherein the step of said encoding said transient frame comprises:

performing a transform analysis of said transient frame for generating in a frequency domain M transient transform coefficients;

performing said transform analysis of at least one further frame for generating in the frequency domain K further transform coefficients, wherein said further frame contains selected samples from both the first frame and the transient frame and said selected samples are chosen based on a predetermined algorithm; and

combining said M transient transform coefficients and said K further transform coefficients using a predetermined procedure, wherein said M+K combined transform coefficient are said M+K encoding values for said transient frame.

5. The method of claim 4, wherein said at least one further frame comprises an ending part of said first frame and a beginning part of said transient frame based on said predetermined algorithm.

6. The method of claim 4, wherein said M transform coefficients correspond to a long transient window with a length of L samples, and said K further transform coefficients correspond to a short transient window with a length of L_s samples, and wherein L and L_s are pre-selected integers with L>

M and L_s>

K.

7. The method of claim 6, wherein said long transient window starts from a first sample of said transient frame and extends over a following frame, and optionally L=2M and L_s=2K.

8. The method of claim 4, wherein said transform analysis is a lapped transform analysis or a modified discrete cosine transform analysis.

9. The method of claim 4, wherein said combining said M transform coefficients and said K further transform coefficients based on said predetermined procedure generates M+K transform coefficients X(j), wherein an index j=0, 1, . . . , M+K−

1 and at least one of said transform coefficients X(M+i) is not equal to zero when a further index i is equal to 0, 1, . . . or K−

1.

10. The method of claim 9, further comprising:

setting said transform coefficients X(M+i) to zero, for completing said encoding said transient frame; and

sending all encoded frames including said transient frame for decoding.

11. The method of claim 10, wherein the method of claim 10 is performed by an electronic device, the method further comprises:

receiving all encoded frames by a further electronic device;

decoding said first frame in the time domain by said further electronic device,

wherein said first encoding method is a time domain codec; and

decoding by said further electronic device said encoded transient frame to said time domain using said non-zero first M transform coefficients in the frequency domain, for compensating transient effects in transform coding.

12. The method of claim 11, wherein said decoding of said encoded transient frame is performed by using at least one of said transform coefficients X(M+i) set to a non-zero value based on a predetermined criterion by said further electronic device.

13. The method of claim 12, wherein said transform coefficients X(M+i) during said decoding are calculated as follows:

X(M+i)=X(M−

K+i) or

X(M+i)=X(M−

i−

1).

14. The method of claim 12, wherein said transform coefficients X(M+i) during said decoding are chosen randomly with a normalized gain, or said transient transform coefficients X(M+i) during said decoding are chosen using linear prediction based on other coefficients out of said transient transform coefficients X(j) using a further predetermined criterion.

15. The method of claim 11, wherein said electronic device is an encoder, an electronic communication device, a mobile communication device or a mobile phone, or said electronic device contains an encoder or a combination of said encoder and a decoder.

16. The method of claim 11, wherein said further electronic device is a decoder, an electronic communication device, a mobile communication device or a mobile phone, or said electronic device contains a decoder or a combination of said decoder and an encoder.

17. A computer program product comprising:

a computer readable storage structure embodying computer program code thereon for execution by a computer processor with said computer program code, wherein said computer program code comprise instructions for performing the method of claim 1.

18. A method for decoding to a time domain a frame of an acoustic signal encoded using a transform based frequency domain codec with M+K transform coefficients X(j), wherein an index j=0, 1, . . . , M+K−

1, and with last K coefficients X(M+i) with a further index i=0, 1, . . . or K−

1 set to zero, comprising;

modifying said M+K transform coefficients X(j) with said K transform coefficients set to zero by setting at least one of said last K transform coefficients X(M+i) to a non-zero value based on a predetermined criterion; and

performing an inverse transform of said M+K transform coefficients after said modifying, for completing said decoding said frame of said acoustic signal to said time domain.

19. The method of claim 18, wherein said transform coefficients X(M+i) during said decoding are calculated as follows:

X(M+i)=X(M−

K+i) or

X(M+i)=X(M−

i−

1).

20. The method of claim 18, wherein said transform coefficients X(M+i) during said decoding are chosen randomly with a normalized gain, or said transient transform coefficients X(M+i) during said decoding are chosen using linear prediction based on other coefficients out of said transient transform coefficients X(j) using a further predetermined criterion.

21. The method of claim 18, wherein said frame of said acoustic signal follows a first frame of said acoustic signal encoded using a first encoding method, and said frame is a transient frame containing M samples and encoded using a second encoding method for producing a set of said M+K transform coefficients X(j), wherein M and K are pre-selected integers of at least a value of one.

22. The method of claim 21, wherein a decision for using said first encoding method or said second encoding method is made based on a pre-selected criterion.

23. The method of claim 21, wherein said first encoding method is a time domain codec, or a code excited linear prediction.

24. The method of claim 21, wherein said encoding said transient frame comprises:

performing a transform analysis of said transient frame for generating in a frequency domain M transient transform coefficients;

performing said transform analysis of at least one further frame for generating in the frequency domain K further transform coefficients, wherein said further frame contains selected samples from both the first frame and the transient frame and said selected samples are chosen based on a predetermined algorithm; and

combining said M transient transform coefficients and said K further transform coefficients using a predetermined procedure, for generating said M+K combined transform coefficient X(j).

25. The method of claim 24, wherein said at least one further frame comprises an ending part of said first frame and a beginning part of said transient frame based on said predetermined algorithm.

26. The method of claim 24, wherein said M transform coefficients correspond to a long transient window with a length of L samples, and said K further transform coefficients correspond to a short transient window with a length of L_s samples, and wherein L and L_s are pre-selected integers with L>

M and L_s>

K.

27. The method of claim 26, wherein said long transient window starts from a first sample of said transient frame and extends over a following frame, and optionally L=2M and L_s=2K.

28. The method of claim 24, wherein said transform analysis is a lapped transform analysis or a modified discrete cosine transform analysis.

29. The method of claim 24, wherein before decoding said transient frame, the method further comprises:

setting said transform coefficients X(M+i) to zero, for completing said encoding said transient frame; and

sending all encoded frames including said transient frame for decoding.

30. The method of claim 29, wherein encoding of said acoustic signal is performed by an electronic device, and before decoding said transient frame, the method further comprises:

receiving all encoded frames by a further electronic device; and

decoding said first frame in the time domain by said further electronic device,

wherein said modifying said M+K transform coefficients X(j) and said performing said inverse transform of said M+K transform coefficients is also performed by said further electronic device.

31. The method of claim 30, wherein said electronic device is an encoder, an electronic communication device, a mobile communication device or a mobile phone, or said electronic device contains an encoder or a combination of said encoder and a decoder.

32. The method of claim 30, wherein said further electronic device is a decoder, an electronic communication device, a mobile communication device or a mobile phone, or said electronic device contains a decoder or a combination of said decoder and an encoder.

33. A computer program product comprising:

a computer readable storage structure embodying computer program code thereon for execution by a computer processor with said computer program code, wherein said computer program code comprises instructions for performing the method of claim 18.

34. An electronic device for encoding an acoustic signal, comprising:

an encoder, for encoding a first frame of the acoustic signal using a first encoding method; and

a transient encoder for encoding a transient frame of an acoustic signal which follows said first frame and contains M samples using a second encoding method for producing a set of M+K encoding values, wherein M and K are pre-selected integers of at least a value of one.

35. The electronic device of claim 34, wherein said electronic device is configured to make a decision for using said first encoding method or said second encoding method based on a pre-selected criterion.

36. The electronic device of claim 34, wherein said first encoding method is a time domain codec, or a code excited linear prediction.

37. The electronic device of claim 34, wherein the transient encoder for the encoding said transient frame comprises:

a long transform window block, for performing a transform analysis of said transient frame for generating in a frequency domain M transient transform coefficients;

a short transform window block, for performing said transform analysis of at least one further frame for generating in the frequency domain K further transform coefficients, wherein said further frame contains selected samples from both the first frame and the transient frame and said selected samples are chosen based on a predetermined algorithm; and

a transform coefficient combining block, for combining said M transient transform coefficients and said K further transform coefficients using a predetermined procedure, wherein said M+K combined transform coefficient are said M+K encoding values for said transient frame.

38. The electronic device of claim 37, wherein said at least one further frame comprises an ending part of said first frame and a beginning part of said transient frame based on said predetermined algorithm.

39. The electronic device of claim 37, wherein said M transform coefficients correspond to a long transient window with a length of L samples, and said K further transform coefficients correspond to a short transient window with a length of L_s samples, and wherein L and L_s are pre-selected integers with L>

M and L_s>

K.

40. The electronic device of claim 39, wherein said long transient window starts from a first sample of said transient frame and extends over a following frame, and optionally L=2M and L_s=2K.

41. The electronic device of claim 37, wherein said transform analysis is a lapped transform analysis or a modified discrete cosine transform analysis.

42. The electronic device of claim 37, wherein said transform coefficient combining block is configured to combine said M transform coefficients and said K further transform coefficients based on said predetermined procedure by generating M+K transform coefficients X(j), wherein an index j=0, 1, . . . , M+K−

1 and at least one of said transform coefficients X(M+i) is not equal to zero when a further index i is equal to 0, 1, . . . or K−

1.

43. The electronic device of claim 42, further comprising:

a transform coefficient removing block, for setting said transform coefficients X(M+i) to zero, for completing said encoding said transient frame; and

a transmitting block for sending all encoded frames including said transient frame for decoding.

44. The electronic device of claim 34, wherein said electronic device is an encoder, an electronic communication device, a mobile communication device or a mobile phone, or said electronic device contains an encoder.

45. An electronic device for decoding to a time domain a frame of an acoustic signal encoded using a transform based frequency domain codec with M+K transform coefficients X(j), wherein an index j=0, 1, . . . , M+K−

1, and with last K coefficients X(M+i) with a further index i=0, 1, . . . or K−

1 set to zero, comprising;

a modification module, for modifying said M+K transform coefficients X(j) with said K transform coefficients set to zero by setting at least one of said last K transform coefficients X(M+i) to a non-zero value based on a predetermined criterion; and

an inverse transform block, for performing an inverse transform of said M+K transform coefficients after said modifying, for completing said decoding said frame of said acoustic signal to said time domain.

46. The electronic device of claim 45, wherein said transform coefficients X(M+i) during said decoding are calculated as follows:

X(M+i)=X(M−

K+i) or

X(M+i)=X(M−

i−

1).

47. The electronic device of claim 45, wherein said modification module is configured to choose transform coefficients X(M+i) during said decoding randomly with a normalized gain, or to choose said transient transform coefficients X(M+i) during said decoding using linear prediction based on other coefficients out of said transient transform coefficients X(j) using a fu rther predetermined criterion.

48. The electronic device of claim 45, wherein said electronic device is a decoder, an electronic communication device, a mobile communication device or a mobile phone, or said electronic device contains a decoder.

49. A system configured for encoding an acoustic signal, comprising:

an encoder, for encoding a first frame of an acoustic signal using a first encoding method; and

a transient encoder for encoding a transient frame of an acoustic signal which follows said first frame and contains M samples using a second encoding method for producing a set of M+K encoding values, wherein M and K are pre-selected integers of at least a value of one.

50. The system of claim 49, wherein a decision for using said first encoding method or said second encoding method is made based on a pre-selected criterion.

51. The system of claim 49, wherein said first encoding method is a time domain codec, or a code excited linear prediction.

52. The system of claim 49, wherein said transient encoder for said encoding said transient frame comprises:

a long transform window block for performing a transform analysis of said transient frame for generating in a frequency domain M transient transform coefficients;

a short transform window block, for performing said transform analysis of at least one further frame for generating in the frequency domain K further transform coefficients, wherein said further frame contains selected samples from both the first frame and the transient frame and said selected samples are chosen based on a predetermined algorithm; and

a transform coefficient combining block, for combining said M transient transform coefficients and said K further transform coefficients using a predetermined procedure, wherein said M+K combined transform coefficient are said M+K encoding values for said transient frame.

53. The system of claim 52, wherein said at least one further frame comprises an ending part of said first frame and a beginning part of said transient frame based on said predetermined algorithm.

54. The system of claim 52, wherein said M transform coefficients correspond to a long transient window with a length of L samples, and said K further transform coefficients correspond to a short transient window with a length of L_s samples, and wherein L and L_s are pre-selected integers with L>

M and L_s>

K.

55. The system of claim 54, wherein said long transient window starts from a first sample of said transient frame and extends over a following frame, and optionally L=2M and L_s=2K.

56. The system of claim 52, wherein said transform analysis is a lapped transform analysis or a modified discrete cosine transform analysis.

57. The system of claim 52, wherein transform coefficient combining block is configured to combine said M transform coefficients and said K further transform coefficients based on said predetermined procedure by generating M+K transform coefficients X(j), wherein an index j=0, 1, . . . , M+K−

1 and at least one of said transform coefficients X(M+i) is not equal to zero when a further index i is equal to 0, 1, . . . or K−

1.

58. The system of claim 57, further comprising:

a transform coefficient removing block, for setting said transform coefficients X(M+i) to zero, for completing said encoding said transient frame; and

a transmitting block for sending all encoded frames including said transient frame for decoding.

59. The system of claim 58, further comprises:

a receiving block for receiving all encoded frames by a further electronic device;

a decoder for decoding said first frame in the time domain by said further electronic device, wherein said first encoding method is a time domain codec; and

a transient decoder of said further electronic device, for decoding said encoded transient frame to said time domain using said non-zero first M transform coefficients in the frequency domain, for compensating transient effects in transform coding.

60. The system of claim 59, wherein said decoding of said encoded transient frame is performed by using at least one of said transform coefficients X(M+i) set to a non-zero value based on a predetermined criterion by said further electronic device.

61. The system of claim 60, wherein said transform coefficients X(M+i) during said decoding are calculated as follows:

X(M+i)=X(M−

K+i) or

X(M+i)=X(M−

i−

1).

62. The system of claim 60, wherein said transform coefficients X(M+i) during said decoding are chosen randomly with a normalized gain, or said transient transform coefficients X(M+i) during said decoding are chosen using linear prediction based on other coefficients out of said transient transform coefficients X(j) using a further predetermined criterion.

63. A system, configured for decoding to a time domain a frame of an acoustic signal encoded using a transform based frequency domain codec with M+K transform coefficients X(j), wherein an index j=0, 1, . . . , M+K−

1, and with last K coefficients X(M+i) with a further index i=0, 1, . . . or K−

1 set to zero, comprising;

a modification module, for modifying said M+K transform coefficients X(j) with said K transform coefficients set to zero by setting at least one of said last K transform coefficients X(M+i) to a non-zero value based on a predetermined criterion; and

an inverse transform block, for performing an inverse transform of said M+K transform coefficients after said modifying, for completing said decoding said frame of said acoustic signal to said time domain.

64. The system of claim 63, wherein said transform coefficients X(M+i) during said decoding are calculated as follows:

X(M+i)=X(M−

K+i) or

X(M+i)=X(M−

i−

1).

65. The system of claim 63, wherein said modification module is configured to choose transform coefficients X(M+i) during said decoding are chosen randomly with a normalized gain, or to choose said transient transform coefficients X(M+i) during said decoding using linear prediction based on other coefficients out of said transient transform coefficients X(j) using a further predetermined criterion.

66. The system of claim 63, wherein said frame of said acoustic signal follows a first frame of said acoustic signal encoded using a first encoding method, and said frame is a transient frame containing M samples and encoded using a second encoding method for producing a set of said M+K transform coefficients X(j), wherein M and K are pre-selected integers of at least a value of one.

67. The system of claim 66, wherein a decision for using said first encoding method or said second encoding method is made based on a pre-selected criterion.

68. The system of claim 66, wherein said first encoding method is a time domain codec, or a code excited linear prediction.

69. The system of claim 66, wherein for facilitating said encoding of said transient frame, the system further comprises:

a long transform window block, for performing a transform analysis of said transient frame for generating in a frequency domain M transient transform coefficients;

a short transform window block, for performing said transform analysis of at least one further frame for generating in the frequency domain K further transform coefficients, wherein said further frame contains selected samples from both the first frame and the transient frame and said selected samples are chosen based on a predetermined algorithm; and

a transform coefficient combining block, for combining said M transient transform coefficients and said K further transform coefficients using a predetermined procedure, for generating said M+K combined transform coefficient X(j).

70. The system of claim 69, wherein said at least one further frame comprises an ending part of said first frame and a beginning part of said transient frame based on said predetermined algorithm.

71. The system of claim 69, wherein said M transform coefficients correspond to a long transient window with a length of L samples, and said K further transform coefficients correspond to a short transient window with a length of L_s samples, and wherein L and L_s are pre-selected integers with L>

M and L_s>

K.

72. The system of claim 71, wherein said long transient window starts from a first sample of said transient frame and extends over a following frame, and optionally L=2M and L_s=2K.

73. The system of claim 69, wherein said transform analysis is a lapped transform analysis or a modified discrete cosine transform analysis.

74. The system of claim 69, further comprises:

a transform coefficient removing block, for setting said transform coefficients X(M+i) to zero, thus completing said encoding said transient frame; and

a transmitting block for sending all encoded frames including said transient frame for decoding.

75. The system of claim 74, further comprises:

a receiving block for receiving all encoded frames; and

a decoder configured for decoding said first frame in the time domain.