Audio Decoding Apparatus and Decoding Method and Program

• US 20090259478A1
• Filed: 02/26/2009
• Published: 10/15/2009
• Est. Priority Date: 07/19/2002
• Status: Active Grant

• Current Assignee: NEC Corporation, Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: NEC Corporation, Panasonic Corporation (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 7,941,319 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

An energy corrector (105) for correcting a target energy for high-frequency components and a corrective coefficient calculator (106) for calculating an energy corrective coefficient from low-frequency subband signals are newly provided. These processors perform a process for correcting a target energy that is required when a band expanding process is performed on a real number only. Thus, a real subband combining filter and a real band expander which require a smaller amount of calculations can be used instead of a complex subband combining filter and a complex band expander, while maintaining a high sound-quality level, and the required amount of calculations and the apparatus scale can be reduced.

Claims

1. An audio decoding apparatus comprising:

a bit stream separator for separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoder for decoding said low-frequency bit stream to generate a low-frequency audio signal;

a subband divider for dividing said low-frequency audio signal into a plurality of complex-valued signals in respective frequency bands to generate low-frequency subband signals;

a corrective coefficient extractor for calculating an energy corrective coefficient based on said low-frequency subband signals;

an energy corrector for correcting a target energy described by said high-frequency bit stream with said energy corrective coefficient to calculate a corrected target energy;

a band expander for generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals as instructed by said high-frequency bit stream, at said corrected target energy; and

a subband combiner for combining real parts of said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

2. An audio decoding apparatus according to claim 1, wherein said corrective coefficient extractor calculates the signal phase of said low-frequency subband signals and calculates the energy corrective coefficient based on said signal phase.

3. An audio decoding apparatus according to claim 1, wherein said corrective coefficient extractor calculates the ratio of the energy of a real part of said low-frequency subband signals and the signal energy of said low-frequency subband signals as the energy corrective coefficient.

4. An audio decoding apparatus according to claim 1, wherein said corrective coefficient extractor averages the phases of samples of said low-frequency subband signals to calculate the energy corrective coefficient.

5. An audio decoding apparatus according to claim 1, wherein said corrective coefficient extractor smooths energy corrective coefficients calculated respectively in said frequency bands.

6. An audio decoding apparatus comprising:

a bit stream separator for separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoder for decoding said low-frequency bit stream to generate a low-frequency audio signal;

a subband divider for dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

a corrective coefficient generator for generating a predetermined energy corrective coefficient;

an energy corrector for correcting a target energy described by said high-frequency bit stream with said energy corrective coefficient to calculate a corrected target energy;

a band expander for generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals as instructed by said high-frequency bit stream, at said corrected target energy; and

a subband combiner for combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

7. An audio decoding apparatus according to claim 6, wherein said corrective coefficient generator generates a random number and uses the random number as said energy corrective coefficient.

8. An audio decoding apparatus according to claim 6, wherein said corrective coefficient generator generates predetermined energy corrective coefficients respectively in the frequency bands.

9. An audio decoding method comprising the steps of:

separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

decoding said low-frequency bit stream to generate a low-frequency audio signal;

dividing said low-frequency audio signal into a plurality of complex-valued signals in respective frequency bands to generate low-frequency subband signals;

calculating an energy corrective coefficient based on said low-frequency subband signals;

correcting a target energy described by said high-frequency bit stream with said energy corrective coefficient to calculate a corrected target energy;

generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals as instructed by said high-frequency bit stream, at said corrected target energy; and

combining real parts of said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

10. An audio decoding method according to claim 9, wherein for calculating said corrected target energy, the signal phase of said low-frequency subband signals is calculated, and the energy corrective coefficient is calculated based on said signal phase.

11. An audio decoding method according to claim 9, wherein for calculating said corrected target energy, the ratio of the energy of a real part of said low-frequency subband signals and the signal energy of said low-frequency subband signals is calculated as the energy corrective coefficient.

12. An audio decoding method according to claim 9, wherein for calculating said corrected target energy, the phases of samples of said low-frequency subband signals are averaged to calculate the energy corrective coefficient.

13. An audio decoding method according to claim 9, wherein for calculating said corrected target energy, energy corrective coefficients calculated respectively in said frequency bands are smoothed.

14. An audio decoding method comprising the steps of:

separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

decoding said low-frequency bit stream to generate a low-frequency audio signal;

dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

generating a predetermined energy corrective coefficient;

correcting a target energy described by said high-frequency bit stream with said energy corrective coefficient to calculate a corrected target energy;

generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals as instructed by said high-frequency bit stream, at said corrected target energy; and

combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

15. An audio decoding method according to claim 14, wherein for generating said energy corrective coefficient, a random number is generated and used as said energy corrective coefficient.

16. An audio decoding method according to claim 14, wherein for generating said energy corrective coefficient, predetermined energy corrective coefficients are generated respectively in the frequency bands.

17. A program for enabling a computer to perform:

a bit stream separating process for separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoding process for decoding said low-frequency bit stream to generate a low-frequency audio signal;

a complex subband dividing process for dividing said low-frequency audio signal into a plurality of complex-valued signals in respective frequency bands to generate low-frequency subband signals;

a corrective coefficient extracting process for calculating an energy corrective coefficient based on said low-frequency subband signals;

an energy correcting process for correcting a target energy described by said high-frequency bit stream with said energy corrective coefficient to calculate a corrected target energy;

a band expanding process for generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals as instructed by said high-frequency bit stream, at said corrected target energy; and

a subband combiner for combining real parts of said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

18. A program according to claim 17, wherein in said corrective coefficient extracting process, the signal phase of said low-frequency subband signals is calculated and the energy corrective coefficient is calculated based on said signal phase.

19. A program according to claim 17, wherein in said corrective coefficient extracting process, the ratio of the energy of a real part of said low-frequency subband signals and the signal energy of said low-frequency subband signals is calculated as the energy corrective coefficient.

20. A program according to claim 17, wherein in said corrective coefficient extracting process, the phases of samples of said low-frequency subband signals are averaged to calculate the energy corrective coefficient.

21. A program according to claim 17, wherein in said corrective coefficient extracting process, energy corrective coefficients calculated respectively in said frequency bands are smoothed.

22. A program for enabling a computer to perform:

a bit stream separating process for separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoding process for decoding said low-frequency bit stream to generate a low-frequency audio signal;

a complex subband dividing process for dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

a corrective coefficient generating process for generating a predetermined energy corrective coefficient;

an energy correcting process for correcting a target energy described by said high-frequency bit stream with said energy corrective coefficient to calculate a corrected target energy;

a band expanding process for generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals as instructed by said high-frequency bit stream, at said corrected target energy; and

a subband combining process for combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

23. A program according to claim 22, wherein in said corrective coefficient generating process, a random number is generated and used as said energy corrective coefficient.

24. A program according to claim 22, wherein in said corrective coefficient generating process, predetermined energy corrective coefficients are generated respectively in the frequency bands.

25. An audio decoding apparatus comprising:

a bit stream separator for separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoder for decoding said low-frequency bit stream to generate a low-frequency audio signal;

a subband divider for dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

an energy corrector for correcting a target energy described by said high-frequency bit stream with a predetermined energy corrective coefficient to calculate a corrected target energy;

a band expander for generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals as instructed by said high-frequency bit stream, at said corrected target energy; and

a subband combiner for combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

26. (canceled)

27. An audio decoding apparatus comprising:

a bit stream separator for separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoder for decoding said low-frequency bit stream to generate a low-frequency audio signal;

a subband divider for dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

an energy corrector for calculating a corrected target energy using an instruction of said high-frequency bit stream and a predetermined energy corrective coefficient;

a band expander for generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals as instructed by said high-frequency bit stream; and

a subband combiner for combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

28. An audio decoding apparatus comprising:

a bit stream separator for separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoder for decoding said low-frequency bit stream to generate a low-frequency audio signal;

a subband divider for dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

a band expander for generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals using an instruction included in said high-frequency bit stream and a predetermined energy corrective coefficient; and

a subband combiner for combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

29. An audio decoding apparatus comprising:

a bit stream separator for separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoder for decoding said low-frequency bit stream to generate a low-frequency audio signal;

a subband divider for dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

a band expander for generating a high-frequency subband signal by correcting the signal energy (Er) of a signal which is generated by copying and processing said low-frequency subband signals, rather than a target energy (R) described by said high-frequency bit stream, with the reciprocal (1/a) of a predetermined energy corrective coefficient (a) when a corrected target energy (aR) which is produced by correcting said target energy (R) with said predetermined energy corrective coefficient (a) and the signal energy (Er) are corrected in amplitude such that the corrected target energy (aR) and the signal energy (Er) are equal to each other; and

a subband combiner for combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

30. An audio decoding method comprising the steps of:

separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

decoding said low-frequency bit stream to generate a low-frequency audio signal;

dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

correcting a target energy described by said high-frequency bit stream with a predetermined energy corrective coefficient to calculate a corrected target energy;

generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals as instructed by said high-frequency bit stream, at said corrected target energy; and

combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

31. (canceled)

32. An audio decoding method comprising the steps of:

separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

decoding said low-frequency bit stream to generate a low-frequency audio signal;

dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals using an instruction included in said high-frequency bit stream and a predetermined energy corrective coefficient; and

combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

33. An audio decoding method comprising the steps of:

separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

decoding said low-frequency bit stream to generate a low-frequency audio signal;

dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals using an instruction included in said high-frequency bit stream and a predetermined energy corrective coefficient; and

a subband combiner for combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

34. An audio decoding method comprising the steps of:

separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

decoding said low-frequency bit stream to generate a low-frequency audio signal;

dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

generating a high-frequency subband signal by correcting the signal energy (Er) of a signal which is generated by copying and processing said low-frequency subband signals, rather than a target energy (R) described by said high-frequency bit stream, with the reciprocal (1/a) of a predetermined energy corrective coefficient (a) when a corrected target energy (aR) which is produced by correcting said target energy (R) with said predetermined energy corrective coefficient (a) and the signal energy (Er) are corrected in amplitude such that the corrected target energy (aR) and the signal energy (Er) are equal to each other; and

combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

35. A program for enabling a computer to perform:

a bit stream separating process for separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoding process for decoding said low-frequency bit stream to generate a low-frequency audio signal;

a subband dividing process for dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

an energy correcting process for correcting a target energy described by said high-frequency bit stream with a predetermined energy corrective coefficient to calculate a corrected target energy;

a band expanding process for generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals as instructed by said high-frequency bit stream, at said corrected target energy; and

a subband combiner for combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

36. A program for enabling a computer to perform:

a bit stream separating process for separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoding process for decoding said low-frequency bit stream to generate a low-frequency audio signal;

a subband dividing process for dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

an energy correcting process for outputting an energy corrective coefficient for a signal which is generated by copying and processing said low-frequency subband signals;

a band expanding process for generating a high-frequency subband signal by correcting, in amplitude, the signal energy of the signal which is generated by copying and processing said low-frequency subband signals as instructed by said high-frequency bit stream, using said energy corrective coefficient; and

a subband combining process for combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

37. A program for enabling a computer to perform:

a bit stream separating process for separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoding process for decoding said low-frequency bit stream to generate a low-frequency audio signal;

a subband dividing process for dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

an energy correcting process for calculating a corrected target energy using an instruction of said high-frequency bit stream and a predetermined energy corrective coefficient;

a band expanding process for generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals as instructed by said high-frequency bit stream; and

a subband combining process for combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

38. A program for enabling a computer to perform:

a bit stream separating process for separating a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoding process for decoding said low-frequency bit stream to generate a low-frequency audio signal;

a subband dividing process for dividing said low-frequency audio signal into a plurality of real-valued signals in respective frequency bands to generate low-frequency subband signals;

a band expanding process for generating a high-frequency subband signal by correcting, in amplitude, the signal energy of a signal which is generated by copying and processing said low-frequency subband signals using an instruction included in said high-frequency bit stream and a predetermined energy corrective coefficient; and

a subband combining process for combining said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

39. (canceled)