BANDWIDTH EXTENSION METHOD, BANDWIDTH EXTENSION APPARATUS, PROGRAM, INTEGRATED CIRCUIT, AND AUDIO DECODING APPARATUS

• US 20120136670A1
• Filed: 06/06/2011
• Published: 05/31/2012
• Est. Priority Date: 06/09/2010
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Corporation of America (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Intellectual Property Corporation of America (Panasonic Holdings Corporation)
• Inventors: Ishikawa, Tomokazu, Norimatsu, Takeshi, Zhou, Huan, Chong, Kok Seng, Zhong, Haishan
• Granted Patent: US 9,093,080 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 21/038 using band spreading techniques
• CPC Class Codes: G10L 21/04 Time compression or expansion

Abstract

To provide a bandwidth extension method which allows reduction of computation amount in bandwidth extension and suppression of deterioration of quality in the bandwidth to be extended. In the bandwidth extension method: a low frequency bandwidth signal is transformed into a QMF domain to generate a first low frequency QMF spectrum; pitch-shifted signals are generated by applying different shifting factors on the low frequency bandwidth signal; a high frequency QMF spectrum is generated by time-stretching the pitch-shifted signals in the QMF domain; the high frequency QMF spectrum is modified; and the modified high frequency QMF spectrum is combined with the first low frequency QMF spectrum.

Claims

1. A bandwidth extension method for producing a full bandwidth signal from a low frequency bandwidth signal, said method comprising:

transforming the low frequency bandwidth signal into a quadrature mirror filter bank (QMF) domain to generate a first low frequency QMF spectrum;

generating pitch-shifted signals by applying different shifting factors on the low frequency bandwidth signal;

generating a high frequency QMF spectrum by time-stretching the pitch-shifted signals in a QMF domain;

modifying the high frequency QMF spectrum to satisfy high frequency energy and tonality conditions; and

generating the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum.

2. The bandwidth extension method according to claim 1,

wherein said generating of a high frequency QMF spectrum includes:

transforming the pitch shifted signals into a QMF domain to generate QMF spectra;

stretching the QMF spectra along a temporal dimension with different stretching factors to generate harmonic patches;

time-aligning the harmonic patches; and

summing up the time-aligned harmonic patches.

3. The bandwidth extension method according to claim 2,

wherein said stretching includes:

calculating the amplitude and phase of a QMF spectrum among the QMF spectra;

manipulating the phase to produce a new phase; and

combining the amplitude with the new phase to generate a new set of QMF coefficients.

4. The bandwidth extension method according to claim 3,

wherein in said manipulating, the new phase is produced on the basis of an original phase of a whole set of QMF coefficients.

5. The bandwidth extension method according to Claim 3,

wherein in said manipulating, manipulation is performed repeatedly for sets of QMF coefficients, and

in said combining, new sets of QMF coefficients are generated.

6. The bandwidth extension method according to claim 3,

wherein in said manipulating, a different manipulation is performed depending on a QMF subband index.

7. The bandwidth extension method according to claim 5,

wherein in said combining, the new sets of QMF coefficients are overlap-added to generate the QMF coefficients corresponding to a temporally-extended audio signal.

8. A bandwidth extension method for producing a full bandwidth signal from a low frequency bandwidth signal, said method comprising:

transforming the low frequency bandwidth signal into a quadrature mirror filter bank (QMF) domain to generate a first low frequency QMF spectrum;

generating a low order harmonic patch by time-stretching the low frequency bandwidth signal in a QMF domain;

generating signals that are pitch shifted, by applying different shift coefficients to the low order harmonic patch, and generating a high frequency QMF spectrum from the signals;

modifying the high frequency QMF spectrum to satisfy high frequency energy and tonality conditions; and

generating the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum.

9. The bandwidth extension method according to claim 8

wherein said generating of a low order harmonic patch includes:

transforming the low frequency bandwidth signal into a second low frequency QMF spectrum;

bandpassing the second low frequency QMF spectrum; and

stretching the bandpassed second low frequency QMF spectrum along a temporal dimension.

10. The bandwidth extension method according to claim 9,

wherein the second low frequency QMF spectrum has finer frequency resolution than the first low frequency QMF spectrum.

11. The bandwidth extension method according to claim 8,

wherein said generating of signals includes:

bandpassing the low order harmonic patch to generate bandpassed patches;

mapping each of the bandpassed patches into high frequency to generate high order harmonic patches; and

summing up the high order harmonic patches with the low order harmonic patch.

12. The bandwidth extension method according to claim 11,

wherein said bandpassing of the low order harmonic patch includes:

splitting each QMF subband in each of the bandpassed patches into multiple sub-subbands;

mapping the sub-subbands to high frequency QMF subbands; and

combining results of the sub-subband mapping.

13. The bandwidth extension method according to claim 12,

wherein said mapping of the sub-subbands to high frequency QMF subbands includes:

dividing the sub-subbands of each of the QMF subbands into a stop band part and a pass band part;

computing transposed center frequencies of the sub-subbands on the pass band part with patch order dependent factor;

mapping the sub-subbands on the pass band part into high frequency QMF subbands according to the center frequencies; and

mapping the sub-subbands on the stop band part into high frequency QMF subbands according to the sub-subbands of the pass band part.

14. A bandwidth extension apparatus that produces a full bandwidth signal from a low frequency bandwidth signal, said bandwidth extension apparatus comprising:

a first transform unit configured to transform the low frequency bandwidth signal into a quadrature mirror filter bank (QMF) domain to generate a first low frequency QMF spectrum;

a pitch-shifting unit configured to generate pitch-shifted signals by applying different shifting factors on the low frequency bandwidth signal;

a high frequency generation unit configured to generate a high frequency QMF spectrum by time-stretching the pitch-shifted signals in a QMF domain;

a spectrum modification unit configured to modify the high frequency QMF spectrum to satisfy high frequency energy and tonality conditions; and

a full bandwidth generation unit configured to generate the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum

15. A bandwidth extension apparatus that produces a full bandwidth signal from a low frequency bandwidth signal, said bandwidth extension apparatus comprising:

a first transform unit configured to transform the low frequency bandwidth signal into a quadrature mirror filter bank (QMF) domain to generate a first low frequency QMF spectrum;

a low order harmonic patch generation unit configured to generate a low order harmonic patch by time-stretching the low frequency bandwidth signal in a QMF domain;

a high frequency generation unit configured to (i) generate signals that are pitch shifted, by applying different shift coefficients to the low order harmonic patch, and (ii) generate a high frequency QMF spectrum from the signals;

a spectrum modification unit configured to modify the high frequency QMF spectrum to satisfy high frequency energy and tonality conditions; and

a full bandwidth generation unit configured to generate the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum.

16. A non-transitory computer-readable recording medium on which a program for producing a full bandwidth signal from a low frequency bandwidth signal is recorded, the program causing a computer to execute:

transforming the low frequency bandwidth signal into a quadrature mirror filter bank (QMF) domain to generate a first low frequency QMF spectrum;

generating pitch-shifted signals by applying different shifting factors on the low frequency bandwidth signal;

generating a high frequency QMF spectrum by time-stretching the pitch-shifted signals in a QMF domain;

modifying the high frequency QMF spectrum to satisfy high frequency energy and tonality conditions; and

generating the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum.

17. A non-transitory computer-readable recording medium on which a program for producing a full bandwidth signal from a low frequency bandwidth signal is recorded, the program causing a computer to execute:

transforming the low frequency bandwidth signal into a quadrature mirror filter bank (QMF) domain to generate a first low frequency QMF spectrum;

generating a low order harmonic patch by time-stretching the low frequency bandwidth signal in a QMF domain;

generating signals that are pitch shifted, by applying different shift coefficients to the low order harmonic patch, and generating a high frequency QMF spectrum from the signals;

modifying the high frequency QMF spectrum to satisfy high frequency energy and tonality conditions; and

generating the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum.

18. An integrated circuit that produces a full bandwidth signal from a low frequency bandwidth signal, said bandwidth extension apparatus comprising:

a first transform unit configured to transform the low frequency bandwidth signal into a quadrature mirror filter bank (QMF) domain to generate a first low frequency QMF spectrum;

a pitch-shifting unit configured to generate pitch-shifted signals by applying different shifting factors on the low frequency bandwidth signal;

a high frequency generation unit configured to generate a high frequency QMF spectrum by time-stretching the pitch-shifted signals in a QMF domain;

a spectrum modification unit configured to modify the high frequency QMF spectrum to satisfy high frequency energy and tonality conditions; and

a full bandwidth generation unit configured to generate the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum

19. An integrated circuit that produces a full bandwidth signal from a low frequency bandwidth signal, said bandwidth extension apparatus comprising:

a first transform unit configured to transform the low frequency bandwidth signal into a quadrature mirror filter bank (QMF) domain to generate a first low frequency QMF spectrum;

a low order harmonic patch generation unit configured to generate a low order harmonic patch by time-stretching the low frequency bandwidth signal in a QMF domain;

a high frequency generation unit configured to (i) generate signals that are pitch shifted, by applying different shift coefficients to the low order harmonic patch, and (ii) generate a high frequency QMF spectrum from the signals;

a spectrum modification unit configured to modify the high frequency QMF spectrum to satisfy high frequency energy and tonality conditions; and

a full bandwidth generation unit configured to generate the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum.

20. An audio decoding apparatus comprising:

a separation unit configured to separate a coded low frequency bandwidth signal from coded information;

a decoding unit configured to decode the coded low frequency bandwidth signal;

a transform unit configured to transform the low frequency bandwidth signal generated through the decoding by said decoding unit, into a quadrature mirror filter bank (QMF) domain to generate a low frequency QMF spectrum;

a pitch-shifting unit configured to generate pitch-shifted signals by applying different shifting factors on the generated low frequency bandwidth signal;

a high frequency generation unit configured to generate a high frequency QMF spectrum by time-stretching the pitch-shifted signals in a QMF domain;

a spectrum modification unit configured to modify the high frequency QMF spectrum to satisfy high frequency energy and tonality conditions;

a full bandwidth generation unit configured to generate the full bandwidth signal by combining the modified high frequency QMF spectrum with the low frequency QMF spectrum; and

an inverse transform unit configured to transform the full bandwidth signal, from a quadrature mirror filter bank (QMF) domain signal to a time domain signal.

21. An audio decoding apparatus comprising:

a separation unit configured to separate a coded low frequency bandwidth signal from coded information;

a decoding unit configured to decode the coded low frequency bandwidth signal;

a transform unit configured to transform the low frequency bandwidth signal generated through the decoding by said decoding unit, into a quadrature mirror filter bank (QMF) domain to generate a low frequency QMF spectrum;

a low order harmonic patch generation unit configured to generate a low order harmonic patch by time-stretching the low frequency bandwidth signal in a QMF domain;

a high frequency generation unit configured to (i) generate signals that are pitch shifted, by applying different shift coefficients to the low order harmonic patch, and (ii) generate a high frequency QMF spectrum from the signals;

a spectrum modification unit configured to modify the high frequency QMF spectrum to satisfy high frequency energy and tonality conditions;

a full bandwidth generation unit configured to generate the full bandwidth signal by combining the modified high frequency QMF spectrum with the low frequency QMF spectrum; and

an inverse transform unit configured to transform the full bandwidth signal, from a quadrature mirror filter bank (QMF) domain signal to a time domain signal.