Subband Harmonic Transposition With Cross-Product Artifact Suppression
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Solution Overview
Problem
Existing harmonic transposition methods in audio coding suffer from high computational complexity and generate unwanted artifacts like ghost pitches and metallic sounds, especially for signals with prominent periodic structures, while achieving high-fidelity audio reproduction.
Innovation Solution
A cross-product enhanced harmonic transposition method using subband block processing, which includes an analysis filter bank, subband processing unit, and synthesis filter bank, applies block-wise phase and magnitude adjustments to reduce intermodulation products, allowing for lower computational effort and improved audio quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex modulated filter banks with fine frequency resolution and high oversampling are used, then audio quality is improved, but computational complexity becomes very high
Solution Approach 1:
The patent divides the frequency spectrum into multiple subbands using a filter bank, processing each subband separately. This segmentation allows for coarser overall frequency resolution while maintaining local processing efficiency, reducing computational complexity compared to processing the entire spectrum with fine resolution
Solution Approach 2:
The patent changes the sampling parameters by applying downsampling factors to different subbands, allowing each subband to be processed at an appropriate resolution. This parameter adaptation reduces the overall oversampling requirement while maintaining audio quality, thereby reducing computational complexity
2Device complexity
If traditional harmonic transposition is applied to signals with prominent periodic structure, then processing is simplified, but ghost pitch and metallic artifacts are generated
Solution Approach 1:
The patent applies different processing characteristics to different subbands. By analyzing the periodic structure in each subband separately and applying localized processing, it preserves harmonic relationships while avoiding the generation of ghost pitches and metallic artifacts that occur with global transposition
Solution Approach 2:
The patent introduces cross-product terms as intermediary elements that capture the interactions between different subbands. These cross-products serve as mediators that reconstruct the full harmonic series information, preventing the loss of harmonic relationships and avoiding artifacts
3Object-generated harmful factors
If cross product enhanced transposition is implemented, then ghost pitch problem is addressed, but computational cost increases considerably
Solution Approach 1:
The patent segments the cross-product computation into individual subband pairs, computing only the necessary cross-terms for each subband combination. This segmented approach reduces the overall computational burden compared to computing all possible cross-products across the entire spectrum
Solution Approach 2:
The patent computes only the essential cross-product terms needed to reconstruct the dominant harmonic relationships, rather than computing all possible cross-products. This partial computation approach achieves adequate ghost pitch suppression while significantly reducing computational cost
Data Source
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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 (101), a subband processing unit (102) configurable by control data (104) and a synthesis filter bank (103).