BANDWIDTH EXTENSION METHOD, BANDWIDTH EXTENSION APPARATUS, PROGRAM, INTEGRATED CIRCUIT, AND AUDIO DECODING APPARATUS
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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.
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Citations
26 Claims
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1-21. -21. (canceled)
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22. A bandwidth extension method for producing a full bandwidth signal from a low frequency bandwidth signal, the low frequency bandwidth signal being an audio signal, said method comprising:
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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 by transforming the low frequency bandwidth signal into a second low frequency QMF spectrum having finer frequency resolution than the first low frequency QMF spectrum; 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 a high frequency energy condition; and generating the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum.
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23. A bandwidth extension apparatus that produces a full bandwidth signal from a low frequency bandwidth signal, the low frequency bandwidth signal being an audio signal, said bandwidth extension apparatus comprising:
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a first transform circuit 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 circuit configured to generate a low order harmonic patch by time-stretching the low frequency bandwidth signal by transforming the low frequency bandwidth signal into a second low frequency QMF spectrum having finer frequency resolution than the first low frequency QMF spectrum; a high frequency generation circuit 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 circuit configured to modify the high frequency QMF spectrum to satisfy a high frequency energy condition; and a full bandwidth generation circuit configured to generate the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum.
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24. 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 low frequency bandwidth signal being an audio signal, the program causing a computer to execute:
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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 by transforming the low frequency bandwidth signal into a second low frequency QMF spectrum having finer frequency resolution than the first low frequency QMF spectrum; 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 a high frequency energy condition; and generating the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum.
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25. An integrated circuit that produces a full bandwidth signal from a low frequency bandwidth signal, the low frequency bandwidth signal being an audio signal, said bandwidth extension apparatus comprising:
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a first transform circuit 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 circuit configured to generate a low order harmonic patch by transforming the low frequency bandwidth signal into a second low frequency QMF spectrum having finer frequency resolution than the first low frequency QMF spectrum; a high frequency generation circuit 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 circuit configured to modify the high frequency QMF spectrum to satisfy a high frequency energy condition; and a full bandwidth generation circuit configured to generate the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum.
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26. An audio decoding apparatus comprising:
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a separation circuit configured to separate a coded low frequency bandwidth signal from coded information; a decoding circuit configured to decode the coded low frequency bandwidth signal; a transform circuit configured to transform the low frequency bandwidth signal generated through the decoding by said decoding circuit, into a quadrature mirror filter bank (QMF) domain to generate a first low frequency QMF spectrum; a low order harmonic patch generation circuit configured to generate a low order harmonic patch by time-stretching the low frequency bandwidth signal by transforming the low frequency bandwidth signal into a second low frequency QMF spectrum having finer frequency resolution than the first low frequency QMF spectrum; a high frequency generation circuit 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 circuit configured to modify the high frequency QMF spectrum to satisfy a high frequency energy condition; and a full bandwidth generation circuit configured to generate the full bandwidth signal by combining the modified high frequency QMF spectrum with the first low frequency QMF spectrum.
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Specification