Subband Block Harmonic Transposition for Audio Quality
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Solution Overview
Problem
Existing harmonic transposition based HFR methods suffer from high computational complexity and reduced audio quality, particularly for transient signals, due to the use of complex filterbanks and oversampling, while also requiring multiple filterbanks for different transposition orders.
Innovation Solution
Implement subband block based harmonic transposition using a single analysis/synthesis filterbank, such as a QMF filterbank, with block-based nonlinear processing to suppress intermodulation products, and adaptively modify nonlinear processing based on signal characteristics to improve audio quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If complex modulated filterbanks with fine frequency resolution and high oversampling are used, then audio quality is improved, but computational complexity increases
Solution Approach 1:
The patent divides the frequency spectrum into subbands using a filterbank structure, processing different frequency regions separately. This segmentation allows for reduced overall complexity while maintaining quality in critical bands, as each subband can be processed with appropriate resolution rather than requiring fine resolution across the entire spectrum.
Solution Approach 2:
The patent applies different processing resolutions to different subbands based on their importance. Critical subbands receive higher processing quality while less critical subbands use lower resolution processing. This local quality approach maintains perceptual audio quality while significantly reducing computational complexity compared to uniform fine resolution processing.
2Adaptability or versatility
If multiple filterbanks are used for different transposition orders, then transposition flexibility is improved, but device complexity increases
Solution Approach 1:
The patent designs a single filterbank structure that can handle multiple transposition orders through adaptive parameter configuration. Rather than implementing separate dedicated filterbanks for each transposition order, the same filterbank infrastructure is used with configurable parameters, achieving multi-functionality and reducing overall system complexity.
Solution Approach 2:
The patent employs dynamic parameter adjustment within the filterbank to adapt to different transposition requirements. The filterbank characteristics can be modified in real-time based on the required transposition order, allowing a single structure to perform multiple functions that would otherwise require multiple static structures.
3Object-generated harmful factors
If block-based nonlinear processing is applied, then intermodulation distortion is reduced, but processing complexity increases
Solution Approach 1:
The patent processes subband signals in blocks rather than continuously, segmenting the processing into discrete temporal segments. This block-based approach reduces intermodulation distortion by limiting the propagation of nonlinear effects while keeping computational complexity manageable through the use of efficient block processing algorithms.
Data Source
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AI summary
The present document relates to audio source coding systems which make use of a harmonic transposition method for high frequency reconstruction (HFR), as well as to digital effect processors, e.g. exciters, where generation of harmonic distortion add brightness to the processed signal, and to time stretchers where a signal duration is prolonged with maintained spectral content. A system and method configured to generate a time stretched and/or frequency transposed signal from an input signal is described. The system comprises an analysis filterbank (101) configured to provide an analysis subband signal from the input signal; wherein the analysis subband signal comprises a plurality of complex valued analysis samples, each having a phase and a magnitude. Furthermore, the system comprises a subband processing unit (102) configured to determine a synthesis subband signal from the analysis subband signal using a subband transposition factor Q and a subband stretch factor S . The subband processing unit (102) performs a block based nonlinear processing wherein the magnitude of samples of the synthesis subband signal are determined from the magnitude of corresponding samples of the analysis subband signal and a predetermined sample of the analysis subband signal. In addition, the system comprises a synthesis filterbank (103) configured to generate the time stretched and/or frequency transposed signal from the synthesis subband signal.