Conversion of synthesized spectral components for encoding and low-complexity transcoding

• US 20040165667A1
• Filed: 06/09/2003
• Published: 08/26/2004
• Est. Priority Date: 02/06/2003
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Truman, Michael Mead, Lennon, Brian Timothy, Andersen, Robert Loring
• Granted Patent: US 7,318,027 B2
• Time in Patent Office: Days
• US Class Current: 375/242
• CPC Class Codes: G10L 19/173 Transcoding, i.e. converting between two coded representations avoiding cascaded coding-decoding

Abstract

In an audio coding system, an encoding transmitter represents encoded spectral components as normalized floating-point numbers. The transmitter provides first and second control parameters that may be used to transcode the encoded spectral parameters. A transcoder uses first control parameters to partially decode the encoded components and uses second control parameters to re-encode the components. The transmitter determines the second control parameters by analyzing the effects of arithmetic operations in the partial-decoding process to identify situations where the floating-point representations lose normalization. Exponents associated with the numbers that lose normalization are modified and the modified exponents are used to calculate the second control parameters.

Claims

1. A method of processing an audio signal comprising:

receiving a signal conveying initial scaled values and initial scale factors representing spectral components of the audio signal, wherein each initial scale factor is associated with one or more initial scaled values, each initial scaled value is scaled according to its associated initial scale factor, and each initial scaled value and associated initial scale factor represent the value of a respective spectral component;

generating coded spectral information by performing a coding process that is responsive to initial spectral information that comprises at least some of the initial scale factors;

deriving one or more first control parameters in response to the initial scale factors and a first bit-rate requirement;

allocating bits according to a first bit allocation process in response to the one or more first control parameters;

obtaining quantized scaled values by quantizing at least some of the initial scaled values using quantizing resolutions based on numbers of bits allocated by the first bit allocation process;

deriving one or more second control parameters in response to at least some of the initial scale factors, one or more modified scale factors and a second bit-rate requirement, wherein the one or more modified scale factors are obtained by;

analyzing the initial spectral information with respect to a synthesis process to be applied to the coded spectral information in a decoding method that generates synthesized spectral components represented by synthesized scaled values and associated synthesized scale factors to identify one or more potentially unnormalized synthesized scaled values, wherein the synthesis process is quasi-inverse to the coding process, and

generating the one or more modified scale factors to represent modified values of initial scale factors in the initial spectral information corresponding to synthesized scale factors that are associated with at least some of the one or more potentially unnormalized synthesized scaled values to compensate for loss of normalization of the identified potentially unnormalized synthesized scaled values; and

assembling encoded information into an encoded signal, wherein the encoded information represents the quantized scaled values, at least some of the initial scale factors, the coded spectral information, the one or more first control parameters and the one or more second control parameters.

2. A method according to claim 1 wherein the coding process performs one or more coding techniques from the set of matrixing, coupling and scale factor formation for spectral component regeneration.

3. A method according to claim 1 wherein:

the coded spectral information comprises coded scaled values associated with initial scale factors or associated with coded scale factors in the coded spectral information generated by the coding process,

the one or more control parameters are derived also in response to at least some of the coded scale factors, and

the quantized scaled values are obtained by also quantizing at least some of the coded scaled values using quantizing resolutions based on numbers of bits allocated by the first bit allocation process.

4. A method according to claim 1 wherein scaled values are floating-point mantissas and scale factors are floating-point exponents.

5. A method according to claim 1 wherein the initial spectral information is analyzed with respect to the synthesis process under worst-case assumptions to identify all potentially over-normalized synthesized scaled values.

6. A method according to claim 5 wherein modified scale factors are generated to compensate for all occurrences of over-normalization of the potentially over-normalized synthesized scaled values.

7. A method according to claim 1 wherein the first bit rate is equal to the second bit rate.

8. A method according to claim 1 wherein the initial spectral information is analyzed by performing at least part of the synthesis process or an emulation of at least part of the synthesis process that is responsive to the coded spectral information and to at least some of the quantized scaled values to generate at least some of the synthesized spectral components, wherein the one or more potentially unnormalized synthesized scaled values are determined to be one or more unnormalized scaled values that result from the synthesis process.

9. A method according to claim 8 wherein all over-normalized synthesized scaled values are identified.

10. A method according to claim 9 wherein modified scale factors are generated to reflect a normalization of all over-normalized synthesized scaled values and at least some under-normalized synthesized scaled values.

11. A method of transcoding encoded audio information comprising:

receiving a first encoded signal conveying first quantized scaled values and first scale factors representing spectral components of an audio signal, wherein each first scale factor is associated with one or more first quantized scaled values, each first quantized scaled value is scaled according to its associated first scale factor, and each first quantized scaled value and associated first scale factor represent a respective spectral component;

deriving second scale factors from the first scale factors;

allocating bits according to a first bit allocation process in response to one or more first control parameters and obtaining dequantized scaled values from the first quantized scaled values by dequantizing according to quantizing resolutions based on numbers of bits allocated by the first bit allocation process;

allocating bits according to a second bit allocation process in response to one or more second control parameters and obtaining second quantized scaled values by quantizing the dequantized scaled values using quantizing resolutions based on numbers of bits allocated by the second bit allocation process; and

assembling the second quantized scaled values, the second scale factors and one or more second control parameters into a second encoded signal.

12. A method according to claim 11 that comprises obtaining the one or more first control parameters and the one or more second control parameters from the first encoded signal.

13. A method according to claim 12, wherein the one or more first control parameters were derived in response to bit-rate requirements of the first encoded signal and the one or more second control parameters were derived in response to bit-rate requirements of the second encoded signal.

14. A method according to claim 11 that comprises deriving the one or more second control parameters from the second scale factors and from bit-rate requirements of the second encoded signal.

15. A method according to claim 11 wherein one or more of the second scale factors are identical to corresponding first scale factors.

16. A method according to claim 11 wherein the first bit allocation process is performed according to a first bit rate for the first encoded signal, and the second bit allocation process is performed according to a second bit rate for the second encoded signal that is equal to the first bit rate.

17. A method according to claim 11 that comprises generating coded spectral information by performing a coding process that is responsive to one or more of the dequantized scaled values.

18. A method according to claim 17 wherein the coding process generates the second scale factors by performing one or more coding techniques from the set of matrixing, dematrixing, coupling, decoupling, scale factor formation for spectral component regeneration, and spectral component regeneration.

19. An encoder for processing an audio signal, wherein the encoder comprises:

means for receiving a signal conveying initial scaled values and initial scale factors representing spectral components of the audio signal, wherein each initial scale factor is associated with one or more initial scaled values, each initial scaled value is scaled according to its associated initial scale factor, and each initial scaled value and associated initial scale factor represent the value of a respective spectral component;

means for generating coded spectral information by performing a coding process that is responsive to initial spectral information that comprises at least some of the initial scale factors;

means for deriving one or more first control parameters in response to the initial scale factors and a first bit-rate requirement;

means for allocating bits according to a first bit allocation process in response to the one or more first control parameters;

means for obtaining quantized scaled values by quantizing at least some of the initial scaled values using quantizing resolutions based on numbers of bits allocated by the first bit allocation process;

means for deriving one or more second control parameters in response to at least some of the initial scale factors, one or more modified scale factors and a second bit-rate requirement, wherein the one or more modified scale factors are obtained by;

analyzing the initial spectral information with respect to a synthesis process to be applied to the coded spectral information in a decoding method that generates synthesized spectral components represented by synthesized scaled values and associated synthesized scale factors to identify one or more potentially unnormalized synthesized scaled values, wherein the synthesis process is quasi-inverse to the coding process, and

generating the one or more modified scale factors to represent modified values of initial scale factors in the initial spectral information corresponding to synthesized scale factors that are associated with at least some of the one or more potentially unnormalized synthesized scaled values to compensate for loss of normalization of the identified potentially unnormalized synthesized scaled values; and

means for assembling encoded information into an encoded signal,

wherein the encoded information represents the quantized scaled values, at least some of the initial scale factors, the coded spectral information, the one or more first control parameters and the one or more second control parameters.

20. An encoder according to claim 19 wherein the coding process performs one or more coding techniques from the set of matrixing, coupling and scale factor formation for spectral component regeneration.

21. An encoder according to claim 19 wherein:

the coded spectral information comprises coded scaled values associated with initial scale factors or associated with coded scale factors in the coded spectral information generated by the coding process,

the one or more control parameters are derived also in response to at least some of the coded scale factors, and

the quantized scaled values are obtained by also quantizing at least some of the coded scaled values using quantizing resolutions based on numbers of bits allocated by the first bit allocation process.

22. An encoder according to claim 19 wherein scaled values are floating-point mantissas and scale factors are floating-point exponents.

23. An encoder according to claim 19 wherein the initial spectral information is analyzed with respect to the synthesis process under worst-case assumptions to identify all potentially over-normalized synthesized scaled values.

24. An encoder according to claim 23 wherein modified scale factors are generated to compensate for all occurrences of over-normalization of the potentially over-normalized synthesized scaled values.

25. An encoder according to claim 19 wherein the first bit rate is equal to the second bit rate.

26. An encoder according to claim 19 wherein the initial spectral information is analyzed by performing at least part of the synthesis process or an emulation of at least part of the synthesis process that is responsive to the coded spectral information and to at least some of the quantized scaled values to generate at least some of the synthesized spectral components, wherein the one or more potentially unnormalized synthesized scaled values are determined to be one or more unnormalized scaled values that result from the synthesis process.

27. An encoder according to claim 26 wherein all over-normalized synthesized scaled values are identified.

28. An encoder according to claim 27 wherein modified scale factors are generated to reflect a normalization of all over-normalized synthesized scaled values and at least some under-normalized synthesized scaled values.

29. A transcoder for transcoding encoded audio information, wherein the transcoder comprises:

means for receiving a first encoded signal conveying first quantized scaled values and first scale factors representing spectral components of an audio signal, wherein each first scale factor is associated with one or more first quantized scaled values, each first quantized scaled value is scaled according to its associated first scale factor, and each first quantized scaled value and associated first scale factor represent a respective spectral component;

means for deriving second scale factors from the first scale factors;

means for allocating bits according to a first bit allocation process in response to one or more first control parameters and obtaining dequantized scaled values from the first quantized scaled values by dequantizing according to quantizing resolutions based on numbers of bits allocated by the first bit allocation process;

means for allocating bits according to a second bit allocation process in response to one or more second control parameters and obtaining second quantized scaled values by quantizing the dequantized scaled values using quantizing resolutions based on numbers of bits allocated by the second bit allocation process; and

means for assembling the second quantized scaled values, the second scale factors and one or more second control parameters into a second encoded signal.

30. A method according to claim 29 that comprises obtaining the one or more first control parameters and the one or more second control parameters from the first encoded signal.

31. A method according to claim 30, wherein the one or more first control parameters were derived in response to bit-rate requirements of the first encoded signal and the one or more second control parameters were derived in response to bit-rate requirements of the second encoded signal.

32. A method according to claim 29 that comprises deriving the one or more second control parameters from the second scale factors and from bit-rate requirements of the second encoded signal.

33. A method according to claim 29 wherein one or more of the second scale factors are identical to corresponding first scale factors.

34. A method according to claim 29 wherein the first bit allocation process is performed according to a first bit rate for the first encoded signal, and the second bit allocation process is performed according to a second bit rate for the second encoded signal that is equal to the first bit rate.

35. A method according to claim 29 that comprises generating coded spectral information by performing a coding process that is responsive to one or more of the dequantized scaled values.

36. A method according to claim 35 wherein the coding process generates the second scale factors by performing one or more coding techniques from the set of matrixing, dematrixing, coupling, decoupling, scale factor formation for spectral component regeneration, and spectral component regeneration.

37. A medium conveying a program of instructions executable by a device, wherein execution of the program of instructions causes the device to perform a method for transcoding audio information, wherein the method comprises:

receiving a signal conveying initial scaled values and initial scale factors representing spectral components of the audio signal, wherein each initial scale factor is associated with one or more initial scaled values, each initial scaled value is scaled according to its associated initial scale factor, and each initial scaled value and associated initial scale factor represent the value of a respective spectral component;

generating coded spectral information by performing a coding process that is responsive to initial spectral information that comprises at least some of the initial scale factors;

deriving one or more first control parameters in response to the initial scale factors and a first bit-rate requirement;

allocating bits according to a first bit allocation process in response to the one or more first control parameters;

obtaining quantized scaled values by quantizing at least some of the initial scaled values using quantizing resolutions based on numbers of bits allocated by the first bit allocation process;

deriving one or more second control parameters in response to at least some of the initial scale factors, one or more modified scale factors and a second bit-rate requirement, wherein the one or more modified scale factors are obtained by;

analyzing the initial spectral information with respect to a synthesis process to be applied to the coded spectral information in a decoding method that generates synthesized spectral components represented by synthesized scaled values and associated synthesized scale factors to identify one or more potentially unnormalized synthesized scaled values, wherein the synthesis process is quasi-inverse to the coding process, and

generating the one or more modified scale factors to represent modified values of initial scale factors in the initial spectral information corresponding to synthesized scale factors that are associated with at least some of the one or more potentially unnormalized synthesized scaled values to compensate for loss of normalization of the identified potentially unnormalized synthesized scaled values; and

assembling encoded information into an encoded signal, wherein the encoded information represents the quantized scaled values, at least some of the initial scale factors, the coded spectral information, the one or more first control parameters and the one or more second control parameters.

38. A medium according to claim 37 wherein the coding process performs one or more coding techniques from the set of matrixing, coupling and scale factor formation for spectral component regeneration.

39. A medium according to claim 37 wherein:

the coded spectral information comprises coded scaled values associated with initial scale factors or associated with coded scale factors in the coded spectral information generated by the coding process,

the one or more control parameters are derived also in response to at least some of the coded scale factors, and

the quantized scaled values are obtained by also quantizing at least some of the coded scaled values using quantizing resolutions based on numbers of bits allocated by the first bit allocation process.

40. A medium according to claim 37 wherein scaled values are floating-point mantissas and scale factors are floating-point exponents.

41. A medium according to claim 37 wherein the initial spectral information is analyzed with respect to the synthesis process under worst-case assumptions to identify all potentially over-normalized synthesized scaled values.

42. A medium according to claim 41 wherein modified scale factors are generated to compensate for all occurrences of over-normalization of the potentially over-normalized synthesized scaled values.

43. A medium according to claim 37 wherein the first bit rate is equal to the second bit rate.

44. A medium according to claim 37 wherein the initial spectral information is analyzed by performing at least part of the synthesis process or an emulation of at least part of the synthesis process that is responsive to the coded spectral information and to at least some of the quantized scaled values to generate at least some of the synthesized spectral components, wherein the one or more potentially unnormalized synthesized scaled values are determined to be one or more unnormalized scaled values that result from the synthesis process.

45. A medium according to claim 44 wherein all over-normalized synthesized scaled values are identified.

46. A medium according to claim 45 wherein modified scale factors are generated to reflect a normalization of all over-normalized synthesized scaled values and at least some under-normalized synthesized scaled values.

47. A medium conveying a program of instructions executable by a device, wherein execution of the program of instructions causes the device to perform a method for transcoding encoded audio information, wherein the method comprises:

receiving a first encoded signal conveying first quantized scaled values and first scale factors representing spectral components of an audio signal, wherein each first scale factor is associated with one or more first quantized scaled values, each first quantized scaled value is scaled according to its associated first scale factor, and each first quantized scaled value and associated first scale factor represent a respective spectral component;

deriving second scale factors from the first scale factors;

allocating bits according to a first bit allocation process in response to one or more first control parameters and obtaining dequantized scaled values from the first quantized scaled values by dequantizing according to quantizing resolutions based on numbers of bits allocated by the first bit allocation process;

allocating bits according to a second bit allocation process in response to one or more second control parameters and obtaining second quantized scaled values by quantizing the dequantized scaled values using quantizing resolutions based on numbers of bits allocated by the second bit allocation process; and

assembling the second quantized scaled values, the second scale factors and one or more second control parameters into a second encoded signal.

48. A medium according to claim 47 that comprises obtaining the one or more first control parameters and the one or more second control parameters from the first encoded signal.

49. A medium according to claim 48, wherein the one or more first control parameters were derived in response to bit-rate requirements of the first encoded signal and the one or more second control parameters were derived in response to bit-rate requirements of the second encoded signal.

50. A medium according to claim 47 that comprises deriving the one or more second control parameters from the second scale factors and from bit-rate requirements of the second encoded signal.

51. A medium according to claim 47 wherein one or more of the second scale factors are identical to corresponding first scale factors.

52. A medium according to claim 47 wherein the first bit allocation process is performed according to a first bit rate for the first encoded signal, and the second bit allocation process is performed according to a second bit rate for the second encoded signal that is equal to the first bit rate.

53. A medium according to claim 47 that comprises generating coded spectral information by performing a coding process that is responsive to one or more of the dequantized scaled values.

54. A medium according to claim 53 wherein the coding process generates the second scale factors by performing one or more coding techniques from the set of matrixing, dematrixing, coupling, decoupling, scale factor formation for spectral component regeneration, and spectral component regeneration.