Bandwidth Extension for Audio Signals Maintaining Harmonic Structure
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Solution Overview
Problem
The existing G.718-SWB audio codec's generic mode for bandwidth extension struggles with maintaining harmonic relationships between low and high frequency band signals, leading to ambiguous spectra and degraded auditory quality, especially for signals with harmonics.
Innovation Solution
The method involves estimating harmonic frequency values from the low frequency spectrum, correcting spectral peaks, and adjusting energy levels to accurately replicate the high frequency spectrum, ensuring the harmonic structure is maintained between the low and high frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If generic mode is used for bandwidth extension by searching for correlated portions from low frequency spectrum, then compression efficiency is improved, but harmonic relationship between low and high frequency bands is lost leading to ambiguous spectra and degraded auditory quality
Solution Approach 1:
The patent changes the approach from generic correlation-based replication to harmonic-specific replication by estimating fundamental frequency and generating harmonics at integer multiples. This parameter-based harmonic generation maintains the harmonic relationship while achieving compression efficiency.
Solution Approach 2:
The patent replaces the generic spectral correlation mechanism with a harmonic synthesis mechanism that uses fundamental frequency estimation and integer multiple generation. This substitution ensures harmonic structure preservation while maintaining compression efficiency.
2Manufacturing precision
If sinusoidal mode is used to maintain harmonic structure, then auditory quality is improved, but device complexity and processing overhead increase
Solution Approach 1:
The patent applies local quality by using sinusoidal harmonic generation only for tonal components where it is most beneficial, while using generic mode for non-tonal portions. This selective application maintains harmonic structure where needed without unnecessarily increasing complexity throughout the entire signal.
Solution Approach 2:
The patent changes the encoding approach by estimating fundamental frequency and generating harmonics at integer multiples, which simplifies the processing compared to full sinusoidal analysis while maintaining harmonic structure accuracy for tonal components.
3Measurement precision
If harmonic frequency estimation and spectral peak correction are performed, then tonal component replication accuracy is improved, but processing time and computational load increase
Solution Approach 1:
The patent performs preliminary spectral peak correction and fundamental frequency estimation before generating harmonics. This preliminary action ensures accurate harmonic placement while streamlining the subsequent processing steps, reducing overall computational load.
Solution Approach 2:
The patent extracts only the essential spectral peaks and fundamental frequency information needed for harmonic generation, rather than processing the entire spectrum. This extraction approach maintains accuracy while reducing processing time and computational requirements.
Data Source
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AI summary
The purpose of the present invention is to more efficiently extend, using a low bit rate, the bandwidth of input signals having a harmonics structure, in order to obtain better audio quality. The present invention is installed in a device that extends bandwidth for audio signal encoding and decoding. This novel bandwidth extension encoding identifies a low-frequency spectrum component having the highest correlation to a high-frequency bandwidth signal among input signals, duplicates a high-frequency spectrum by energy adjustment of said component, and maintains the harmonic relationship between the low-frequency spectrum and the duplicated high-frequency spectrum by adjusting the spectral peak position of the duplicated high-frequency spectrum, on the basis of a harmonic frequency estimated from a composite low-frequency spectrum.