Spectral translation/ folding in the subband domain
First Claim
1. Method for obtaining an envelope adjusted and frequency-translated signal by high-frequency spectral reconstruction of complex subband signals in channels within a reconstruction range using complex subband signals in source area channels derived from a lowband signal, using a digital filter bank having an analysis part (201) and a synthesis part (202), the reconstruction range including channel frequencies which are higher than frequencies in the source area channels, the method comprising the following steps:
- filtering the lowband signal by means of the analysis part (201) to obtain the complex subband signals in the source area channels;
calculating a number of consecutive complex subband signals in channels within the reconstruction range using a number of frequency-translated consecutive complex subband signals in the source area channels and an envelope correction for obtaining a predetermined spectral envelope, wherein a complex subband signal in a source area channel having an index i is frequency-translated to a complex subband signal in a reconstruction range channel having an index j, and wherein a complex subband signal in a source area channel having an index i+1 is frequency-translated to a complex subband signal in a reconstruction range channel having an index j+1, and filtering the consecutive complex subband signals in channels within the reconstruction range by means of the synthesis part to obtain an envelope adjusted and frequency-translated signal.
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Abstract
The present invention relates to a new method and apparatus for improvement of High Frequency Reconstruction (HFR) techniques using frequency translation or folding or a combination thereof. The proposed invention is applicable to audio source coding systems, and offers significantly reduced computational complexity. This is accomplished by means of frequency translation or folding in the subband domain, preferably integrated with spectral envelope adjustment in the same domain. The concept of dissonance guard-band filtering is further presented. The proposed invention offers a low-complexity, intermediate quality HFR method useful in speech and natural audio coding applications.
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Citations
23 Claims
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1. Method for obtaining an envelope adjusted and frequency-translated signal by high-frequency spectral reconstruction of complex subband signals in channels within a reconstruction range using complex subband signals in source area channels derived from a lowband signal, using a digital filter bank having an analysis part (201) and a synthesis part (202), the reconstruction range including channel frequencies which are higher than frequencies in the source area channels, the method comprising the following steps:
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filtering the lowband signal by means of the analysis part (201) to obtain the complex subband signals in the source area channels;
calculating a number of consecutive complex subband signals in channels within the reconstruction range using a number of frequency-translated consecutive complex subband signals in the source area channels and an envelope correction for obtaining a predetermined spectral envelope, wherein a complex subband signal in a source area channel having an index i is frequency-translated to a complex subband signal in a reconstruction range channel having an index j, and wherein a complex subband signal in a source area channel having an index i+1 is frequency-translated to a complex subband signal in a reconstruction range channel having an index j+1, and filtering the consecutive complex subband signals in channels within the reconstruction range by means of the synthesis part to obtain an envelope adjusted and frequency-translated signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 18, 23)
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13. Method for obtaining an envelope adjusted and frequency-folded signal by high-frequency spectral reconstruction of complex subband signals in channels within a reconstruction range using complex subband signals in source area channels derived from a lowband signal, using a digital filter bank having an analysis part (201) and a synthesis part (202), the reconstruction range including channel frequencies which are higher than frequencies in the source area channels, the method comprising the following steps:
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filtering the lowband signal by means of the analysis part (201) to obtain the complex subband signals in the source area channels;
calculating a number of consecutive complex subband signals in channels within the reconstruction range using a number of frequency-translated consecutive conjugate complex subband signals in the source area channels and an envelope correction for obtaining a predetermined spectral envelope, wherein a complex subband signal in a source area channel having an index i is frequency-folded to a complex subband signal in a reconstruction range channel having an index j, and wherein a complex subband signal in a source area channel having an index i+1 is frequency-folded to a complex subband signal in a reconstruction range channel having an index j−
1, and filtering the consecutive complex subband signals in channels within the reconstruction range by means of the synthesis part to obtain an envelope adjusted and frequency-translated signal. - View Dependent Claims (14, 15, 16, 17)
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19. Apparatus for obtaining an envelope adjusted and frequency-translated signal by high-frequency spectral reconstruction of complex subband signals in channels within a reconstruction range using complex subband signals in source area channels derived from a lowband signal, using a digital filter bank having an analysis part (201) and a synthesis part (202), the reconstruction range including channel frequencies which are higher than frequencies in the source area channels, comprising:
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means for filtering the lowband signal by means of the analysis part (201) to obtain the complex subband signals in the source area channels;
means for calculating a number of consecutive complex subband signals in channels within the reconstruction range using a number of frequency-translated consecutive complex subband signals in the source area channels and an envelope correction for obtaining a predetermined spectral envelope, wherein a complex subband signal in a source area channel having an index i is frequency-translated to a complex subband signal in a reconstruction range channel having an index j, and wherein a complex subband signal in a source area channel having an index i+1 is frequency-translated to a complex subband signal in a reconstruction range channel having an index j+1, and means for filtering the consecutive complex subband signals in channels within the reconstruction range by means of the synthesis part to obtain an envelope adjusted and frequency-translated signal. - View Dependent Claims (21, 22)
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20. Apparatus for obtaining an envelope adjusted and frequency-folded signal by high-frequency spectral reconstruction of complex subband signals in channels within a reconstruction range using complex subband signals in source area channels derived from a lowband signal, using a digital filter bank having an analysis part (201) and a synthesis part (202), the reconstruction range including channel frequencies which are higher than frequencies in the source area channels, comprising:
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means for filtering the lowband signal by means of the analysis part (201) to obtain the complex subband signals in the source area channels;
means for calculating a number of consecutive complex subband signals in channels within the reconstruction range using a number of frequency-translated consecutive conjugate complex subband signals in the source area channels and an envelope correction for obtaining a predetermined spectral envelope, wherein a complex subband signal in a source area channel having an index i is frequency-folded to a complex subband signal in a reconstruction range channel having an index j, and wherein a complex subband signal in a source area channel having an index i+1 is frequency-folded to a complex subband signal in a reconstruction range channel having an index j−
1, andmeans for filtering the consecutive complex subband signals in channels within the reconstruction range by means of the synthesis part to obtain an envelope adjusted and frequency-translated signal.
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Specification