Audio decoding apparatus and decoding method and program

• US 7,941,319 B2
• Filed: 02/26/2009
• Issued: 05/10/2011
• 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: Takamizawa, Yuichiro, Tanaka, Naoya, Tsushima, Mineo, Neo, Sua Hong, Serizawa, Masahiro, Kuah, Kim Hann, Shimada, Osamu, Chong, Kok Seng, Nomura, Toshiyuki, Norimatsu, Takeshi
• Primary Examiner(s): Vo; Huyen X.
• Application Number:
  US12/393,316
• Publication Number:
  US 20090259478A1
• Time in Patent Office: 803 Days
• Field of Search: 704/205, 704/219, 704/200, 704/228, 704500-504
• 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 that separates a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoder that decodes said low-frequency bit stream to generate a low-frequency audio signal;

a subband divider that divides 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 that calculates an energy corrective coefficient based on said low-frequency subband signals;

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

a band expander that generates 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 that combines real parts of said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal,

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.

2. The audio decoding apparatus according to claim 1, wherein said corrective coefficient extractor smoothes energy corrective coefficients calculated respectively in said frequency bands.

3. An audio decoding apparatus comprising:

a bit stream separator that separates a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoder that decodes said low-frequency bit stream to generate a low-frequency audio signal;

a subband divider that divides 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 that calculates an energy corrective coefficient based on said low-frequency subband signals;

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

a band expander that generates 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 that combines real parts of said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal,

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. The audio decoding apparatus according to claim 3, wherein said corrective coefficient extractor smoothes energy corrective coefficients calculated respectively in said frequency bands.

5. An audio decoding apparatus comprising:

a bit stream separator that separates a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoder that decodes said low-frequency bit stream to generate a low-frequency audio signal;

a subband divider that divides 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 that calculates an energy corrective coefficient based on said low-frequency subband signals;

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

a band expander that generates 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 that combines real parts of said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal,

wherein said corrective coefficient extractor averages the phases of samples of said low-frequency subband signals to calculate the energy corrective coefficient.

6. The audio decoding apparatus according to claim 5, wherein said corrective coefficient extractor smoothes energy corrective coefficients calculated respectively in said frequency bands.

7. 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,

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.

8. The audio decoding method according to claim 7, wherein for calculating said corrected target energy, energy corrective coefficients calculated respectively in said frequency bands are smoothed.

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,

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.

10. The 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.

11. 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,

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.

12. The audio decoding method according to claim 11, wherein for calculating said corrected target energy, energy corrective coefficients calculated respectively in said frequency bands are smoothed.

13. A non-transitory computer-readable medium storing a program which causes a computer to perform:

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

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

a complex subband dividing process that divides said low-frequency audio signal into a plurality of signals in respective ands to generate low-frequency subband signals;

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

an energy correcting process that corrects 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 that generates 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 that combines real parts of said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal,

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.

14. The non-transitory computer-readable medium according to claim 13, wherein in said corrective coefficient extracting process, energy corrective coefficients calculated respectively in said frequency bands are smoothed.

15. A non-transitory computer-readable medium storing a program which causes a computer to perform:

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

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

a complex subband dividing process that divides said low-frequency audio signal into a plurality of signals frequency bands to generate low-frequency subband signals;

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

an energy correcting process that corrects 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 that generates 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 that combines real parts of said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal,

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.

16. The non-transitory computer-readable medium according to claim 15, wherein in said corrective coefficient extracting process, energy corrective coefficients calculated respectively in said frequency bands are smoothed.

17. A non-transitory computer-readable medium storing a program which causes a computer to perform:

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

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

a complex subband dividing process that divides 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 that calculates an energy corrective coefficient based on said low-frequency subband signals;

an energy correcting process that corrects 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 that generates 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 that combines real parts of said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal,

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.

18. The non-transitory computer-readable medium according to claim 17, wherein in said corrective coefficient extracting process, energy corrective coefficients calculated respectively in said frequency bands are smoothed.

19. An audio decoding apparatus comprising:

a bit stream separator that separates a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoder that decodes said low-frequency bit stream to generate a low-frequency audio signal;

a subband divider that divides 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 that generates 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 that combines said low-frequency subband signals and said high-frequency subband signals to produce a decoded audio signal.

20. 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.

21. An audio decoding apparatus comprising:

a bit stream separator that separates a bit stream into a low-frequency bit stream and a high-frequency bit stream;

a low-frequency decoder that decodes said low-frequency bit stream to generate a low-frequency audio signal;

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

an energy corrector that outputs an energy corrective coefficient for real-valued copied subband signals which are used to generate real-valued high-frequency subband signals;

a band expander that generates real-valued copied subband signals by copying from said real-valued low-frequency subband signals using said high-frequency bit stream, and that generates said real-valued high-frequency subband signals by correcting, in amplitude, the signal energy of said real-valued copied subband signals using said energy corrective coefficient,

wherein the high-frequency bit stream contains copying information indicative of which one of the low-frequency subbands a real-valued low-frequency signal is to be copied from to generate a high-frequency subband, and signal processing information representing a signal processing process to be performed on the real-valued low-frequency signal,

wherein said energy corrective coefficient is adapted to convert a target energy of complex-valued high-frequency subband signals, included in said high-frequency bit stream, into a target energy of said real-valued high-frequency subband signals; and

a subband combiner that combines said real-valued low-frequency subband signals and said real-valued high-frequency subband signals to produce a decoded audio signal.