Subband Harmonic Transposition to Suppress HFR Intermodulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing high-frequency reconstruction (HFR) methods in audio source coding systems face challenges in achieving high-fidelity audio reproduction at low 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 oversampling.
Innovation Solution
The implementation of cross-product enhanced HFR using a system that processes complex-valued analysis subband signals in blocks, applying subband transposition and stretching factors, and nonlinear frame processing to generate time-stretched and frequency-transposed signals with reduced intermodulation products, allowing for coarser frequency resolution and lower oversampling without compromising quality.
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 of spectral reconstruction is improved, but device complexity increases significantly
Solution Approach 1:
The patent divides the audio signal into multiple subbands using a filter bank, where each subband is processed independently with lower computational requirements. This segmentation allows coarse frequency resolution per subband while maintaining overall high spectral reconstruction quality through the combination of multiple subbands.
Solution Approach 2:
The patent applies different processing strategies to different subbands based on their local characteristics. By adapting the processing to local spectral features rather than applying uniform fine resolution across all frequencies, the system achieves high local spectral quality with reduced global computational complexity.
2Manufacturing precision
If fine frequency resolution is used to avoid intermodulation distortion, then manufacturing precision of spectral reconstruction is improved, but device complexity increases
Solution Approach 1:
The patent segments the frequency spectrum into multiple subbands, allowing each subband to be processed with coarser resolution while the collective output achieves the required spectral precision. This avoids the computational burden of fine resolution across the entire frequency range.
3Manufacturing precision
If high degree of oversampling in time is applied to avoid alias type distortion, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent processes each subband separately with appropriate oversampling factors tailored to that subband's characteristics, rather than uniformly oversampling the entire signal. This segmented approach reduces the total computational load while maintaining precision where needed.
4Ease of operation
If traditional harmonic transposition is used for signals with prominent periodic structure, then ease of operation is maintained, but object-generated harmful factors increase due to ghost pitch and metallic character
Solution Approach 1:
The patent segments the harmonic signal into multiple subbands and applies transposition to each subband independently. This prevents the generation of ghost pitches that occur when transposing entire harmonic series, as each subband contains only a portion of the harmonic content. The segmented processing maintains operational simplicity while eliminating the metallic character artifact.
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.