Method and Device for Efficient Frame Erasure Concealment in Speech Codecs

• US 20110125505A1
• Filed: 12/28/2006
• Published: 05/26/2011
• Est. Priority Date: 12/28/2005
• Status: Active Grant

• Current Assignee: VoiceAge EVS LLC (SoftBank Group Corp.)
• Original Assignee: VoiceAge Corporation
• Inventors: Salami, Redwan, Gournay, Philleppe, Jelinek, Milan, Vaillancourt, Tommy
• Granted Patent: US 8,255,207 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm

Abstract

A method and device for concealing frame erasures caused by frames of an encoded sound signal erased during transmission from an encoder to a decoder and for recovery of the decoder after frame erasures comprise, in the encoder, determining concealment/recovery parameters including at least phase information related to frames of the encoded sound signal. The concealment/recovery parameters determined in the encoder are transmitted to the decoder and, in the decoder, frame erasure concealment is conducted in response to the received concealment/recovery parameters. The frame erasure concealment comprises resynchronizing, in response to the received phase information, the erasure-concealed frames with corresponding frames of the sound signal encoded at the encoder. When no concealment/recovery parameters are transmitted to the decoder, a phase information of each frame of the encoded sound signal that has been erased during transmission from the encoder to the decoder is estimated in the decoder. Also, frame erasure concealment is conducted in the decoder in response to the estimated phase information, wherein the frame erasure concealment comprises resynchronizing, in response to the estimated phase information, each erasure-concealed frame with a corresponding frame of the sound signal encoded at the encoder.

Claims

1. A method for concealing frame erasures caused by frames of an encoded sound signal erased during transmission from an encoder to a decoder and for recovery of the decoder after frame erasures, the method comprising:

in the encoder, determining concealment/recovery parameters including at least phase information related to frames of the encoded sound signal;

transmitting to the decoder the concealment/recovery parameters determined in the encoder; and

in the decoder, conducting frame erasure concealment in response to the received concealment/recovery parameters, wherein the frame erasure concealment comprises resynchronizing the erasure-concealed frames with corresponding frames of the encoded sound signal by aligning a first phase-indicative feature of the erasure-concealed frames with a second phase-indicative feature of the corresponding frames of the encoded sound signal, said second phase-indicative feature being included in the phase information.

2. A method as defined in claim 1, wherein determination of the concealment/recovery parameters comprises determining as the phase information a position of a glottal pulse in each frame of the encoded sound signal.

3. A method as defined in claim 1, wherein determination of the concealment/recovery parameters comprises determining as the phase information a position and sign of a last glottal pulse in each frame of the encoded sound signal.

4. A method as defined in claim 2, further comprising quantizing the position of the glottal pulse prior to transmitting the position of the glottal pulse to the decoder.

5. A method as defined in claim 3, further comprising quantizing the position and sign of the last glottal pulse prior to transmitting the position and sign of the last glottal pulse to the decoder.

6. A method as defined in claim 4, further comprising encoding the quantized position of the glottal pulse into a future frame of the encoded sound signal.

7. A method as defined in claim 2, wherein determining the position of the glottal pulse comprises:

measuring the glottal pulse as a pulse of maximum amplitude in a predetermined pitch cycle of each frame of the encoded sound signal; and

determining the position of the pulse of maximum amplitude.

9. A method as defined in claim 3, wherein determining the position of the last glottal pulse comprises:

measuring the last glottal pulse as a pulse of maximum amplitude in each frame of the encoded sound signal; and

determining the position of the pulse of maximum amplitude.

10. A method as defined in claim 9, wherein determining the sign of the glottal pulse comprises:

measuring a sign of the maximum amplitude pulse.

11. A method as defined in claim 10, wherein resynchronizing an erasure-concealed frame with a corresponding frame of the encoded sound signal comprises:

decoding the position and sign of the last glottal pulse of said corresponding frame of the encoded sound signal;

determining, in the erasure-concealed frame, a position of a maximum amplitude pulse having a sign similar to the sign of the last glottal pulse of the corresponding frame of the encoded sound signal, closest to the position of said last glottal pulse of said corresponding frame of said encoded sound signal; and

aligning the position of the maximum amplitude pulse in the erasure-concealed frame with the position of the last glottal pulse of the corresponding frame of the encoded sound signal.

12. A method as defined in claim 7, wherein resynchronizing an erasure-concealed frame with a corresponding frame of the encoded sound signal comprises:

decoding the position of the glottal pulse of said corresponding frame of the encoded sound signal;

determining, in the erasure-concealed frame, a position of a maximum amplitude pulse closest to the position of said glottal pulse of said corresponding frame of said encoded sound signal; and

aligning the position of the maximum amplitude pulse in the erasure-concealed frame with the position of the glottal pulse of the corresponding frame of the encoded sound signal.

13. A method as defined in claim 12, wherein aligning the position of the maximum amplitude pulse in the erasure-concealed frame with the position of the glottal pulse in the corresponding frame of the encoded sound signal comprises:

determining an offset between the position of the maximum amplitude pulse in the erasure-concealed frame and the position of the glottal pulse in the corresponding frame of the encoded sound signal; and

inserting/removing in the erasure-concealed frame a number of samples corresponding to the determined offset.

14. A method as defined in claim 13, wherein inserting/removing the number of samples comprises:

determining at least one region of minimum energy in the erasure-concealed frame; and

distributing the number of samples to be inserted/removed around the at least one region of minimum energy.

15. A method as defined in claim 14, wherein distributing the number of samples to be inserted/removed around the at least one region of minimum energy comprises distributing the number of samples around the at least one region of minimum energy using the following relation:

16. A method as defined in claim 15, wherein R(i) is in increasing order, so that samples are mostly added/removed towards an end of the erasure-concealed frame.

17. A method as defined in claim 1, wherein conducting frame erasure concealment in response to the received concealment/recovery parameters comprises, for voiced erased frames:

constructing a periodic part of an excitation signal in the erasure-concealed frame in response to the received concealment/recovery parameters; and

constructing a random innovative part of the excitation signal by randomly generating a non-periodic, innovative signal.

18. A method as defined in claim 1, wherein conducting frame erasure concealment in response to the received concealment/recovery parameters comprises, for unvoiced erased frames, constructing a random innovative part of an excitation signal by randomly generating a non-periodic, innovative signal.

19. A method as defined in claim 1, wherein the concealment/recovery parameters further include signal classification.

20. A method as defined in claim 19, wherein the signal classification comprises classifying successive frames of the encoded sound signal as unvoiced, unvoiced transition, voiced transition, voiced, or onset.

21. A method as defined in claim 20, wherein the classification of a lost frame is estimated based on the classification of a future frame and a last received good frame.

22. A method as defined in claim 21, wherein the classification of the lost frame is set to voiced if the future frame is voiced and the last received good frame is onset.

23. A method as defined in claim 22, wherein the classification of the lost frame is set to unvoiced transition if the future frame is unvoiced and the last received good frame is voiced.

24. A method as defined in claim 1, wherein:

the sound signal is a speech signal;

determination, in the encoder, of concealment/recovery parameters includes determining the phase information and a signal classification of successive frames of the encoded sound signal;

conducting frame erasure concealment in response to the concealment/recovery parameters comprises, when an onset frame is lost which is indicated by the presence of a voiced frame following frame erasure and an unvoiced frame before frame erasure, artificially reconstructing the lost onset frame; and

resynchronizing the erasure-concealed, lost onset frame in response to the phase information with the corresponding onset frame of the encoded sound signal.

25. A method as defined in claim 24, wherein artificially reconstructing the lost onset frame comprises artificially reconstructing a last glottal pulse in the lost onset frame as a low-pass filtered pulse.

26. A method as defined in claim 24, further comprising scaling the reconstructed lost onset frame by a gain.

27. A method as defined in claim 1, comprising, when the phase information is not available at the time of concealing an erased frame, updating the content of an adaptive codebook of the decoder with the phase information when available before decoding a next received, non erased frame.

28. A method as defined in claim 1, wherein:

determining the concealment/recovery parameters comprises determining as the phase information a position of a glottal pulse in each frame of the encoded sound signal; and

updating the adaptive codebook comprises resynchronizing the glottal pulse in the adaptive codebook.

29. A method as defined in claim 1, wherein the first phase-indicative feature of the erasure-concealed frame comprises a position of a pulse of maximum amplitude and the second phase-indicative feature of the encoded sound signal comprises a position of a glottal pulse.

8. A method as defined in 7, further comprising determining as phase information a sign of the glottal pulse by measuring a sign of the maximum amplitude pulse.

30. A method for concealing frame erasures caused by frames of an encoded sound signal erased during transmission from an encoder to a decoder and for recovery of the decoder after frame erasures, the method comprising, in the decoder:

estimating a phase information of each frame of the encoded sound signal that has been erased during transmission from the encoder to the decoder; and

conducting frame erasure concealment in response to the estimated phase information, wherein the frame erasure concealment comprises resynchronizing each erasure-concealed frame with a corresponding frame of the encoded sound signal by aligning a first phase-indicative feature of each erasure-concealed frame with a second phase-indicative feature of the corresponding frame of the encoded sound signal, said second phase-indicative feature being included in the estimated phase information.

31. A method as defined in claim 30, wherein estimating the phase information comprises estimating a position of a last glottal pulse of each frame of the encoded sound signal that has been erased.

32. A method as defined in claim 31, wherein estimating the position of the last glottal pulse of each frame of the encoded sound signal that has been erased comprises:

estimating a glottal pulse from a past pitch value; and

interpolating the estimated glottal pulse with the past pitch value so as to determine estimated pitch lags.

33. A method as defined in claim 32, wherein resynchronizing an erasure-concealed frame with the corresponding frame of the encoded sound signal comprises:

determining a maximum amplitude pulse in the erasure-concealed frame; and

aligning the maximum amplitude pulse in the erasure-concealed frame with the estimated glottal pulse.

34. A method as defined in claim 33, wherein aligning the maximum amplitude pulse in the erasure-concealed frame with the estimated glottal pulse comprises:

calculating pitch cycles in the erasure-concealed frame;

determining an offset between the estimated pitch lags and the pitch cycles in the erasure-concealed frame; and

inserting/removing a number of samples corresponding to the determined offset in the erasure-concealed frame.

35. A method as defined in claim 34, wherein inserting/removing the number of samples comprises:

determining at least one region of minimum energy in the erasure-concealed frame; and

distributing the number of samples to be inserted/removed around the at least one region of minimum energy.

36. A method as defined in claim 35, wherein distributing the number of samples to be inserted/removed around the at least one region of minimum energy comprises distributing the number of samples around the at least one region of minimum energy using the following relation:

37. A method as defined in claim 36, wherein R(i) is in increasing order, so that samples are mostly added/removed towards the end of the erasure-concealed frame.

38. A method as defined in claim 30, comprising attenuating a gain of each erasure-concealed frame, in a linear manner, from the beginning to the end of the erasure-concealed frame.

39. A method as defined in claim 38, wherein the gain of each erasure-concealed frame is attenuated until a is reached, wherein a is a factor for controlling a converging speed of the decoder recovery after frame erasure.

40. A method as defined in claim 39, wherein the factor a is dependent on stability of a LP filter for unvoiced frames.

41. A method as defined in claim 40, wherein the factor a further takes into consideration an energy evolution of voiced segments.

42. A method as defined in claim 30, wherein the first phase-indicative feature of each erasure-concealed frame comprises a position of a pulse of maximum amplitude and the second phase-indicative feature of the encoded sound signal comprises an estimated position of a glottal pulse.

43. A device for concealing frame erasures caused by frames of an encoded sound signal erased during transmission from an encoder to a decoder and for recovery of the decoder after frame erasures, the device comprising:

in the encoder, means for determining concealment/recovery parameters including at least phase information related to frames of the encoded sound signal;

means for transmitting to the decoder the concealment/recovery parameters determined in the encoder; and

in the decoder, means for conducting frame erasure concealment in response to the received concealment/recovery parameters, wherein the means for conducting frame erasure concealment comprises means for resynchronizing the erasure-concealed frames with corresponding frames of the encoded sound signal by aligning a first phase-indicative feature of the erasure-concealed frames with a second phase-indicative feature of the corresponding frames of the encoded sound signal, said second phase-indicative feature being included in the phase information.

44. A device for concealing frame erasures caused by frames of an encoded sound signal erased during transmission from an encoder to a decoder and for recovery of the decoder after frame erasures, the device comprising:

in the encoder, a generator of concealment/recovery parameters including at least phase information related to frames of the encoded sound signal;

a communication link for transmitting to the decoder concealment/recovery parameters determined in the encoder; and

in the decoder, a frame erasure concealment module supplied with the received concealment/recovery parameters and comprising a synchronizer responsive to the received phase information to resynchronize the erasure-concealed frames with corresponding frames of the encoded sound signal by aligning a first phase-indicative feature of the erasure-concealed frames with a second phase-indicative feature of the corresponding frames of the encoded sound signal, said second phase-indicative feature being included in the phase information.

45. A device as defined in claim 44, wherein the generator of concealment/recovery parameters generates as the phase information a position of a glottal pulse in each frame of the encoded sound signal.

46. A device as defined in claim 44, wherein the generator of concealment/recovery parameters generates as the phase information a position and sign of a last glottal pulse in each frame of the encoded sound signal.

47. A device as defined in claim 45, further comprising a quantizer for .quantizing the position of the glottal pulse prior to transmission of the position of the glottal pulse to the decoder, via the communication link.

48. A device as defined in claim 46, further comprising a quantizer for quantizing the position and sign of the last glottal pulse prior to transmission of the position and sign of the last glottal pulse to the decoder, via the communication link.

49. A device as defined in claim 47, further comprising an encoder of the quantized position of the glottal pulse into a future frame of the encoded sound signal.

50. A device as defined in claim 45, wherein the generator determines as the position of the glottal pulse a position of a maximum amplitude pulse in each frame of the encoded sound signal.

51. A device as defined in claim 46, wherein the generator determines as the position and sign of the last glottal pulse a position and sign of a maximum amplitude pulse in each frame of the encoded sound signal.

52. A device as defined in claim 50, wherein the generator determines as phase information a sign of the glottal pulse as a sign of the maximum amplitude pulse.

53. A device as defined in claim 50, wherein the synchronizer:

determines in each erasure-concealed frame, a position of a maximum amplitude pulse closest to the position of the glottal pulse in a corresponding frame of the encoded sound signal;

determines an offset between the position of the maximum amplitude pulse in each erasure-concealed frame and the position of the glottal pulse in the corresponding frame of the encoded sound signal; and

inserts/removes a number of samples corresponding to the determined offset in each erasure-concealed frame so as to align the position of the maximum amplitude pulse in the erasure-concealed frame with the position of the glottal pulse in the corresponding frame of the encoded sound signal.

54. A device as defined in claim 46, wherein the synchronizer:

determines in each erasure-concealed frame, a position of a maximum amplitude pulse having a sign similar to the sign of the last glottal pulse, closest to the position of the last glottal pulse in a corresponding frame of the encoded sound signal;

determines an offset between the position of the maximum amplitude pulse in each erasure-concealed frame and the position of the last glottal pulse in the corresponding frame of the encoded sound signal; and

inserts/removes a number of samples corresponding to the determined offset in each erasure-concealed frame so as to align the position of the maximum amplitude pulse in the erasure-concealed frame with the position of the last glottal pulse in the corresponding frame of the encoded sound signal.

55. A device as defined in claim 53, wherein the synchronizer further:

determines at least one region of minimum energy in each erasure-concealed frame by using a sliding window; and

distributes the number of samples to be inserted/removed around the at least one region of minimum energy.

56. A device as defined in claim 55, wherein the synchronizer uses the following relation for distributing the number of samples to be inserted/removed around the at least one region of minimum energy:

57. A device as defined in claim 56, wherein R(i) is in increasing order, so that samples are mostly added/removed towards an end of the erasure-concealed frame.

58. A device as defined in claim 44, wherein the frame erasure concealment module supplied with the received concealment/recovery parameters comprises, for voiced erased frames:

a generator of a periodic part of an excitation signal in each erasure-concealed frame in response to the received concealment/recovery parameters; and

a random generator of a non-periodic, innovative part of the excitation signal.

59. A device as defined in claim 44, wherein the frame erasure concealment module supplied with the received concealment/recovery parameters comprises, for unvoiced erased frames, a random generator of a non-periodic, innovative part of an excitation signal.

60. A device as defined in claim 44, wherein the decoder updates, when the phase information is not available at the time of concealing an erased frame, the content of an adaptive codebook of the decoder with the phase information when available before decoding a next received, non erased frame.

61. A device as defined in claim 60, wherein:

the generator of concealment/recovery parameters determines as the phase information a position of a glottal pulse in each frame of the encoded sound signal; and

the decoder, for updating the adaptive codebook, resynchronizes the glottal pulse in the adaptive codebook.

62. A device as defined in claim 44, wherein the first phase-indicative feature of the erasure-concealed frames comprises a position of a pulse of maximum amplitude and the second phase-indicative feature of the encoded sound signal comprises a position of a glottal pulse.

63. A device for concealing frame erasures caused by frames of an encoded sound signal erased during transmission from an encoder to a decoder and for recovery of the decoder after frame erasures, the device comprising:

means for estimating, at the decoder, a phase information of each frame of the encoded sound signal that has been erased during transmission from the encoder to the decoder; and

means for conducting frame erasure concealment in response to the estimated phase information, the means for conducting frame erasure concealment comprising means for resynchronizing each erasure-concealed frame with a corresponding frame of the encoded sound by aligning a first phase-indicative feature of each erasure-concealed frame with a second phase-indicative feature of the corresponding frame of the encoded sound signal, said second phase-indicative feature being included in the estimated phase information.

64. A device for concealing frame erasures caused by frames of an encoded sound signal erased during transmission from an encoder to a decoder and for recovery of the decoder after frame erasures, the device comprising:

at the decoder, an estimator of a phase information of each frame of the encoded signal that has been erased during transmission from the encoder to the decoder; and

an erasure concealment module supplied with the estimated phase information and comprising a synchronizer which, in response to the estimated phase information, resynchronizes each erasure-concealed frame with a corresponding frame of the encoded sound signal by aligning a first phase-indicative feature of each erasure-concealed frame with a second phase-indicative feature of the corresponding frame of the encoded sound signal, said second phase-indicative feature being included in the estimated phase information.

65. A device as defined in claim 64, wherein the estimator of the phase information estimates, from a past pitch value, a position and sign of a last glottal pulse in each frame of the encoded sound signal, and interpolates the estimated glottal pulse with the past pitch value so as to determine estimated pitch lags.

66. A device as defined in claim 65, wherein the synchronizer:

determines a maximum amplitude pulse and pitch cycles in each erasure-concealed frame;

determines an offset between the pitch cycles in each erasure-concealed frame and the estimated pitch lags in the corresponding frame of the encoded sound signal; and

inserts/removes a number of samples corresponding to the determined offset in each erasure-concealed frame so as to align the maximum amplitude pulse in the erasure-concealed frame with the estimated last glottal pulse.

67. A device as defined in claim 66, wherein the synchronizer further:

determines at least one region of minimum energy by using a sliding window; and

distributes the number of samples around the at least one region of minimum energy.

68. A device as defined in claim 67, wherein the synchronizer uses the following relation for distributing the number of samples around the at least one region of minimum energy:

69. A device as defined in claim 68, wherein R(i) is in increasing order, so that samples are mostly added/removed towards an end of the erasure-concealed frame.

70. A device as defined in claim 65, further comprising an attenuator for attenuating a gain of each erasure-concealed frame, in a linear manner, from a beginning to an end of the erasure-concealed frame.

71. A device as defined in claim 70, wherein the attenuator attenuates the gain of each erasure-concealed frame until a, wherein a is a factor for controlling a converging speed of the decoder recovery after frame erasure.

72. A device as defined in claim 71, wherein the factor a is dependent on stability of a LP filter for unvoiced frames.

73. A device as defined in claim 72, wherein the factor a further takes into consideration an energy evolution of voiced segments.

74. A device as defined in claim 64, wherein the first phase-indicative feature of each erasure-concealed frame comprises a position of a pulse of maximum amplitude and the second phase-indicative feature of the encoded sound signal comprises an estimated position of a glottal pulse.