Audio decoding device, decoding method, and program

• US 7,555,434 B2
• Filed: 06/24/2003
• Issued: 06/30/2009
• 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
• Primary Examiner(s): Vo; Huyen X.
• Application Number:
  US10/485,616
• Publication Number:
  US 20050171785A1
• Time in Patent Office: 2,198 Days
• Field of Search: 704500-504, 704/219, 704/205, 704/264, 704/200, 704/216, 704/224, 704/220, 708/206, 708/228
• 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 real-valued signals in respective frequency bands to generate low-frequency subband signals;

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

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

wherein said energy corrector calculates the signal phase of said low-frequency subband signals and calculates the energy corrective coefficient based on said signal phase.

2. An audio decoding apparatus according to claim 1, wherein said energy corrector 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 said energy corrective coefficient.

3. An audio decoding apparatus according to claim 2, wherein said energy corrector smoothes said energy corrective coefficients calculated in respective frequency bands.

4. An audio decoding apparatus according to claim 1, wherein said energy corrector calculates the averages of real part of said low-frequency subband signals to the signal energy of said low-frequency subband signals as said energy corrective coefficient.

5. An audio decoding apparatus according to 4, wherein said energy corrector smoothes said energy corrective coefficients calculated in respective frequency bands.

6. An audio decoding apparatus according to claim 1, wherein said energy corrector smoothes said energy corrective coefficients calculated in respective frequency bands.

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

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

wherein said band expander is adapted for generating said copied subband signals by copying from said low-frequency subband signals using said high-frequency bit stream, and for generating said high-frequency subband signals by correcting, in amplitude, the signal energy (Er) of said copied subband signals by using a gain which is calculated by dividing a target energy (R) of high-frequency subband signals, described in said high-frequency bit stream by the product of said signal energy (Er) and the reciprocal (1/a) of said a predetermined energy corrective coefficient (a).

8. 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;

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

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

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

wherein said outputting step calculates the signal phase of said low-frequency subband signals and calculates the energy corrective coefficient based on said signal phase.

9. An audio decoding method according to claim 8, wherein said outputting step 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 said energy corrective coefficient.

10. An audio decoding method according to claim 9, wherein said outputting step smoothes said energy corrective coefficients calculated in respective frequency bands.

11. An audio decoding method according to claim 8, wherein said outputting step calculates the averages of real part of said low-frequency subband signals to the signal energy of said low-frequency subband signals as said energy corrective coefficient.

12. An audio decoding method according to claim 11, wherein said outputting step smoothes said energy corrective coefficients calculated in respective frequency bands.

13. An audio decoding method according to claim 8, wherein said outputting step smoothes said energy corrective coefficients calculated in respective frequency bands.

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;

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

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

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

wherein said generating step generates said copied subband signals by copying from said low-frequency subband signals using said high-frequency bit stream, and for generating said high-frequency subband signals by correcting, in amplitude, the signal energy (Er) of said copied subband signals by using a gain which is calculated by dividing a target energy (R) of high-frequency subband signals, described in said high-frequency bit stream by the product of said signal energy (Er) and the reciprocal (1/a) of said a predetermined energy corrective coefficient (a).

15. A computer-readable recording medium storing 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,

wherein said energy correcting process calculates the signal phase of said low-frequency subband signals and calculates the energy corrective coefficient based on said signal phase.

16. A computer-readable recording medium according to claim 15, wherein said energy correcting process 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 said energy corrective coefficient.

17. A computer-recording medium according to claim 16, wherein said energy correcting process smoothes said energy corrective coefficients calculated in respective frequency bands.

18. A computer-readable recording medium according to claim 15, wherein said energy correcting process calculates the averages of real part of said low-frequency subband signals to the signal energy of said low-frequency subband signals as said energy corrective coefficient.

19. A computer-readable recording medium according to claim 18, wherein said energy correcting process smoothes said energy corrective coefficients calculated in respective frequency bands.

20. A computer-readable recording medium according to claim 15, wherein said energy correcting process smoothes said energy corrective coefficients calculated in respective frequency bands.

21. A computer-readable recording medium storing 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,

wherein said band expanding process generates said copied subband signals by copying from said low-frequency subband signals using said high-frequency bit stream, and for generating said high-frequency subband signals by correcting, in amplitude, the signal energy (Er) of said copied subband signals by using a gain which is calculated by dividing a target energy (R) of high-frequency subband signals, described in said high-frequency bit stream by the product of said signal energy (Er) and the reciprocal (1/a) of said a predetermined energy corrective coefficient (a).