Audio decoding apparatus and method

• US 20050149339A1
• Filed: 09/11/2003
• Published: 07/07/2005
• Est. Priority Date: 09/19/2002
• Status: Active Grant

• Current Assignee: NEC Corporation, Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: NEC Corporation, Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Shimada, Osamu, Chong, Kok Seng, Nomura, Toshiyuki, Norimatsu, Takeshi, Takamizawa, Yuichiro, Tanaka, Naoya, Tsushima, Mineo, Neo, Sua Hong, Serizawa, Masahiro, Kuah, Kim Hann
• Granted Patent: US 7,069,212 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

An audio decoding apparatus decodes high frequency component signals using a band expander that generates multiple high frequency subband signals from low frequency subband signals divided into multiple subbands and transmitted high frequency encoded information. The apparatus is provided with an aliasing detector and an aliasing remover. The aliasing detector detects the degree of occurrence of aliasing components in the multiple high frequency subband signals generated by the band expander. The aliasing remover suppresses aliasing components in the high frequency subband signals by adjusting the gain used to generate the high frequency subband signals. Thus occurrence of aliasing can be suppressed and the resulting degradation in sound quality can be reduced, even when real-valued subband signals are used in order to reduce the number of operations.

Claims

1. An audio decoding apparatus for decoding a wideband audio signal from a bitstream containing encoded information for a narrowband audio signal, comprising:

a bitstream demultiplexer that demultiplexes encoded information from the bitstream;

a decoder that decodes a narrowband audio signal from the demultiplexed encoded information;

an analysis filter bank that divides the decoded narrowband audio signal into multiple first subband signals;

a band expander that generates multiple second subband signals from at least one first subband signal, each second subband signal having a higher frequency band than the frequency band of the first subband signals;

an aliasing remover that adjusts a gain of the second subband signal in order to suppress the aliasing components occurring in the second subband signals; and

a real-valued calculation synthesis filter bank that synthesizes the first subband signal and second subband signal to obtain a wideband audio signal.

2. An audio decoding apparatus for decoding a wideband audio signal from a bitstream containing encoded information for a narrowband audio signal, comprising:

a bitstream demultiplexer that demultiplexes encoded information from the bitstream;

a decoder that decodes a narrowband audio signal from the demultiplexed encoded information;

an analysis filter bank that divides the decoded narrowband audio signal into multiple first subband signals;

a band expander that generates multiple second subband signals from at least one first subband signal, each second subband signal having a higher frequency band than the frequency band of the first subband signals;

an aliasing detector that detects a degree of occurrence of aliasing components in the multiple second subband signals generated by the band expander;

an aliasing remover that adjusts a gain of the second subband signal based on the detected degree of occurrence of aliasing components to suppress the aliasing components; and

a real-valued calculation synthesis filter bank that synthesizes the first subband signal and second subband signal to obtain a wideband audio signal.

3. The audio decoding apparatus as described in claim 2, wherein aliasing components contain at least components that are suppressed after synthesis by a synthesis filter bank which performs a complex-valued calculation.

4. The audio decoding apparatus as described in claim 2, wherein the first subband signal is a low frequency subband signal, and the second subband signal is a high frequency subband signal.

5. The audio decoding apparatus as described in claim 4, wherein the aliasing detector uses a parameter denoting a slope of a frequency distribution of the first subband signal to detect the degree of occurrence of aliasing components.

6. The audio decoding apparatus as described in claim 5, wherein the aliasing detector evaluates a parameter denoting a slope of a frequency distribution in two adjacent subbands, and detects the degree of occurrence of aliasing components in the two subbands.

7. The audio decoding apparatus as described in claim 5, wherein the aliasing detector evaluates a parameter denoting a slope of a frequency distribution in three adjacent subbands, and detects the degree of occurrence of aliasing components in the three subbands.

8. The audio decoding apparatus as described in claim 5, wherein the parameter denoting the slope of the frequency distribution is a reflection coefficient.

9. The audio decoding apparatus as described in claim 2, wherein

the bitstream contains encoded information for a narrowband audio signal and additional information used for enabling narrowband to wideband,

the additional information containing high frequency component information describing a feature of a signal in a higher frequency band than the frequency band of the first subband signals;

and

the bitstream demultiplexer further demultiplexes the additional information from the bitstream; and

the band expander generates multiple second subband signals in a higher frequency band than the frequency band of the first subband signals from at least one first subband signal and the high frequency component information in the additional information.

10. The audio decoding apparatus as described in claim 9, wherein the high frequency component information contains gain information for a higher frequency band than the frequency band of the first subband signals;

the band expander generates the second subband signal from the first subband signal based on the gain information; and

the aliasing remover adjusts a gain of the second subband signal based on the detected degree of occurrence of aliasing components and gain information in order to suppress the aliasing components.

11. The audio decoding apparatus as described in claim 9, wherein the high frequency component information contains energy information for signals at higher frequency band than the frequency band of the first subband signals;

the band expander generates the second subband signal from the first subband signal based on gain information calculated from the energy information; and

the aliasing remover adjusts a gain of the second subband signal based on the detected degree of occurrence of aliasing components and gain information in order to suppress the aliasing components.

12. The audio decoding apparatus as described in claim 11, wherein the aliasing remover adjusts a gain of the second subband signal so that the total energy of the multiple second subband signals with adjusted gain is equal to the total energy provided by the energy information of the corresponding second subband signals.

13. An audio decoding apparatus as described in claim 11, wherein the band expander adds an additional signal to the generated second subband signal;

the energy information contains energy R of the second subband signal and ratio Q between the energy R and the energy of the additional signal; and

the band expander calculates energy E of the first subband signal, and calculates gain g of the corresponding second subband signal based on energy R, energy E, and the energy of the additional signal represented by energy ratio Q.

14. The audio decoding apparatus as described in claim 13, wherein gain g of the second subband signal is

g=sqrt{R/E/(1+Q)}

where sqrt is a square root operator.

15. An audio decoding method for decoding a wideband audio signal from a bitstream containing encoded information for a narrowband audio signal, comprising:

demultiplexing encoded information from the bitstream;

decoding a narrowband audio signal from the demultiplexed encoded information;

dividing the decoded narrowband audio signal into multiple first subband signals;

generating multiple second subband signals from at least one first subband signal, each second subband signal having a higher frequency band than the frequency band of the first subband signals;

adjusting a gain of the second subband signal in order to suppress the aliasing components occurring in the second subband signals; and

synthesizing the first subband signal and the second subband signal with a real-valued filtering calculation to obtain the wideband audio signal.

29. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 15.

30. A data recording medium for storing the software according to claim 29.

16. An audio decoding method for decoding a wideband audio signal from a bitstream containing encoded information for a narrowband audio signal, comprising:

demultiplexing encoded information from the bitstream;

decoding a narrowband audio signal from the demultiplexed encoded information;

dividing the decoded narrowband audio signal into multiple first subband signals;

generating multiple second subband signals from at least one first subband signal, each second subband signal having a higher frequency band than the frequency band of the first subband signals;

detecting a degree of occurrence of aliasing components in each of the generated multiple second subband signals before the second subband signals are generated;

adjusting a gain of the second subband signal based on the detected degree of occurrence of aliasing components in order to suppress the aliasing components; and

synthesizing the first subband signal and the second subband signal with a real-valued filtering calculation to obtain the wideband audio signal.

17. The audio decoding method as described in claim 16, wherein aliasing components contain at least components that are suppressed after synthesizing with a complex-valued filtering calculation.

18. The audio decoding method as described in claim 16, wherein the first subband signal is a low frequency subband signal, and the second subband signal is a high frequency subband signal.

19. The audio decoding method as described in claim 18, wherein in the detecting a degree, a parameter denoting a slope of a frequency distribution of the first subband signal is used to detect the degree of occurrence of aliasing components.

20. The audio decoding method as described in claim 19, wherein in the detecting a degree, a parameter denoting a slope of a frequency distribution in two adjacent subbands is evaluated to detect the degree of occurrence of aliasing components in the two subbands.

21. The audio decoding method as described in claim 19, wherein in the detecting a degree, a parameter denoting a slope of a frequency distribution in three adjacent subbands is evaluated to detect the degree of occurrence of aliasing components in the three subbands.

22. The audio decoding method as described in claim 19, wherein the parameter denoting the slope of the frequency distribution is a reflection coefficient.

23. The audio decoding method as described in claim 16, wherein

the bitstream contains encoded information for a narrowband audio signal and additional information used for enabling narrowband to wideband,

the additional information contains high frequency component information describing a feature of a signal in a higher frequency band than the frequency band of the first subband signals;

and

in the demultiplexing encoded information, the additional information is demultiplexed from the bitstream; and

in the generating multiple second subband signals, multiple second subband signals in a higher frequency band than the frequency band of the first subband signals is generated from at least one first subband signal and the high frequency component information in the additional information.

24. The audio decoding method as described in claim 23, wherein the high frequency component information contains gain information for a higher frequency band than the frequency band of the first subband signals;

in the generating multiple second subband signals, the second subband signal is generated from the first subband signal based on the gain information; and

in the adjusting a gain, the gain of the second subband signal is adjusted based on the detected degree of occurrence of aliasing components and gain information in order to suppress the aliasing components.

25. The audio decoding method as described in claim 23, wherein the high frequency component information contains energy information for signals at higher frequency band than the frequency band of the first subband signals;

in the generating multiple second subband signals, the second subband signal is generated from the first subband signal based on gain information calculated from the energy information; and

in the adjusting a gain, the gain of the second subband signal is adjusted based on the detected degree of occurrence of aliasing components and gain information in order to suppress the aliasing components.

26. The audio decoding method as described in claim 25, wherein in the adjusting a gain, the gain of the second subband signal is adjusted so that the total energy of the multiple second subband signals with adjusted gain is equal to the total energy provided by the energy information of the corresponding second subband signals.

27. An audio decoding method as described in claim 25, wherein the generating multiple second subband signals, includes adding an additional signal to the generated second subband signal,

the energy information contains energy R of the second subband signal and ratio Q between the energy R and the energy of the additional signal;

and

the generating multiple second subband signals further includes, calculating energy E of the first subband signal, and calculating gain g of the corresponding second subband signal based on energy R, energy E, and the energy of the additional signal represented by energy ratio Q.

28. The audio decoding method as described in claim 27, wherein gain g of the second subband signal is

g=sqrt{R/E/(1+Q)}

where sqrt is a square root operator.

31. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 16.

32. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 17.

33. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 18.

34. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 19.

35. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 20.

36. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 21.

37. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 22.

38. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 23.

39. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 24.

40. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 25.

41. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 26.

42. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 27.

43. Software coded in a programming language that provides a function achieved by the audio decoding method according to claim 28.

44. A data recording medium for storing the software according to claim 31.

45. A data recording medium for storing the software according to claim 32.

46. A data recording medium for storing the software according to claim 33.

47. A data recording medium for storing the software according to claim 34.

48. A data recording medium for storing the software according to claim 35.

49. A data recording medium for storing the software according to claim 36.

50. A data recording medium for storing the software according to claim 37.

51. A data recording medium for storing the software according to claim 38.

52. A data recording medium for storing the software according to claim 39.

53. A data recording medium for storing the software according to claim 40.

54. A data recording medium for storing the software according to claim 41.

55. A data recording medium for storing the software according to claim 42.

56. A data recording medium for storing the software according to claim 43.