Cross-Product Subband Harmonic Transposition for Ghost Pitch Suppression
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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 at reduced computational complexity, particularly for signals with prominent periodic structures, leading to artifacts like 'ghost' pitches and increased computational complexity due to the need for fine frequency resolution and high oversampling.
Innovation Solution
A system and method employing cross-product enhanced subband block-based harmonic transposition, which processes complex subband samples in blocks to reduce intermodulation products, allowing for coarser frequency resolution and lower oversampling while maintaining high output quality, by using a subband processing unit that determines synthesis subband signals through nonlinear frame processing and overlap-and-add techniques.
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, then audio quality is improved, but computational complexity becomes very high
Solution Approach 1:
The patent segments the audio signal into multiple subbands using a filter bank, processing each subband independently. This segmentation allows for coarser frequency resolution within each subband while maintaining overall 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. By using subband-specific processing with appropriate resolution and oversampling factors tailored to each band's characteristics, the system achieves high audio quality where needed while reducing computational load in less critical regions.
2Device complexity
If conventional harmonic transposition is used for signals with prominent periodic structure, then processing is simpler, but ghost pitch artifacts and metallic character occur
Solution Approach 1:
The patent introduces cross-product terms that combine multiple subband signals to generate additional harmonic components. This dimensional expansion in the signal processing domain allows for more accurate reconstruction of periodic structures, eliminating ghost pitch artifacts while maintaining computational efficiency through the structured cross-product formulation.
3Device complexity
If single sideband modulation based HFR is used, then implementation is simpler, but dissonant ringing artifacts result
Solution Approach 1:
The patent combines multiple subband signals through cross-product operations to create a composite transposed signal. This composite approach integrates information from multiple frequency bands, effectively suppressing dissonant ringing artifacts that would arise from simpler single-band transposition methods.
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.