Cross-Product Harmonic Transposition for High-Frequency Reconstruction
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Solution Overview
Problem
Existing harmonic transposition methods in audio coding systems, such as harmonic transposition and single sideband modulation, face issues with artifacts like 'ghost' pitches and metallic sounds, especially for periodic signals, and require complex computational processes to avoid these artifacts.
Innovation Solution
A method and system that uses a nonlinear combination of multiple analysis subbands in a filter bank to generate high frequency components by modifying phases and magnitudes, incorporating cross-product enhancements to ensure complete harmonic series reconstruction, addressing periodic signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional harmonic transposition methods are used to reconstruct high frequency components, then computational complexity is reduced, but artifacts such as 'ghost' pitches and metallic sounds appear in periodic signals
Solution Approach 1:
The patent segments the transposition process into multiple stages: first applying cross-product enhancement to generate intermediate frequency components, then applying harmonic transposition to generate final high frequency components. This segmentation allows each stage to address specific aspects of the signal, reducing artifacts while maintaining computational efficiency.
Solution Approach 2:
The patent applies cross-product enhancement as a preliminary action before harmonic transposition. By pre-processing the low frequency signal to enhance cross-products, the subsequent harmonic transposition operates on improved input data, which prevents the generation of ghost pitches and metallic sounds without requiring complex post-processing.
2Ease of operation
If single sideband modulation is used for high frequency reconstruction, then the method is simpler to implement, but dissonant ringing artifacts occur and the cross over frequency is higher
Solution Approach 1:
The patent introduces cross-product enhancement as an intermediary process between the input signal and the harmonic transposition stage. This intermediary step processes the signal to prevent the formation of dissonant ringing artifacts, allowing the use of simpler harmonic transposition methods while avoiding their typical drawbacks.
3Manufacturing precision
If multiple orders of transposition are applied to avoid spectral gaps in periodic signals, then harmonic series completeness is improved, but computational complexity increases significantly
Solution Approach 1:
The patent applies cross-product enhancement as a preliminary action that pre-generates many of the harmonic components that would otherwise require multiple transposition orders. By doing this work in advance, the system achieves complete harmonic series with a single transposition order, avoiding the computational burden of multiple sequential transpositions.
Solution Approach 2:
The cross-product enhancement process creates copies and combinations of frequency components that represent the complete harmonic series. Instead of generating harmonics through multiple iterative transpositions, the method directly copies and combines frequency components to produce the full harmonic content in one step.
Data Source
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AI summary
The present invention relates to audio coding systems which make use of a harmonic transposition method for high frequency reconstruction (HFR). A system and a method for generating a high frequency component of a signal from a low frequency component of the signal is described. The system comprises an analysis filter bank providing a plurality of analysis subband signals of the low frequency component of the signal. It also comprises a non-linear processing unit to generate a synthesis subband signal with a synthesis frequency by modifying the phase of a first and a second of the plurality of analysis subband signals and by combining the phase-modified analysis subband signals. Finally, it comprises a synthesis filter bank for generating the high frequency component of the signal from the synthesis subband signal.