Cross product enhanced subband block based harmonic transposition
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Solution Overview
Problem
Existing high-frequency reconstruction (HFR) methods in audio source coding systems face challenges in achieving high-fidelity audio reproduction while maintaining low computational complexity, particularly for signals with prominent periodic structures.
Innovation Solution
The proposed system employs a cross-product enhanced subband block-based harmonic transposition method, which processes complex subband samples in blocks to apply frame-wise phase offsets and magnitude adjustments, reducing intermodulation products and allowing for coarser frequency resolution and lower oversampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If complex modulated filter banks with very fine frequency resolution and high degree of oversampling are employed to achieve high audio quality, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the audio signal into multiple subbands using filter banks, processing each subband separately. This segmentation allows for coarser frequency resolution within each subband while maintaining overall high audio quality, thereby reducing computational complexity compared to processing the entire spectrum with fine resolution.
Solution Approach 2:
The patent applies different processing strategies to different subbands based on their local characteristics. By adapting the processing to local spectral properties rather than applying uniform fine resolution across all frequencies, the system achieves high audio quality where needed while reducing computational burden in less critical regions.
2Reliability
If harmonic transposition is applied to signals with prominent periodic structures, then high frequency reconstruction is achieved, but object-generated harmful factors increase due to ghost pitch and metallic character
Solution Approach 1:
The patent exploits the periodic structure of signals with prominent pitch by using cross-products of subband signals to generate harmonics. Instead of treating the periodicity as a source of ghost pitch artifacts, the invention converts it into a benefit by using the periodic structure to predict and reconstruct high-frequency harmonics more accurately, thereby reducing artifacts while maintaining reconstruction quality.
Data Source
AI summary
The invention provides an efficient implementation of cross-product enhanced high-frequency reconstruction (HFR), wherein a new component at frequency QΩ+rΩ0 is generated on the basis of existing components at Ω and Ω+Ω0. The invention provides a block-based harmonic transposition, wherein a time block of complex subband samples is processed with a common phase modification. Superposition of several modified samples has the net effect of limiting undesirable intermodulation products, thereby enabling a coarser frequency resolution and/or lower degree of oversampling to be used. In one embodiment, the invention further includes a window function suitable for use with block-based cross-product enhanced HFR. A hardware embodiment of the invention may include an analysis filter bank, a subband processing unit configurable by control data and a synthesis filter bank.