Audio Decoding Frequency Regeneration to Reduce Low-Bitrate Artifacts
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Solution Overview
Problem
Current audio codecs face challenges in maintaining perceptual quality at low bitrates due to limitations in bandwidth extension techniques, which result in artifacts like dissonance, beating, and increased computational complexity, especially in mobile devices.
Innovation Solution
A signal-adaptive approach that performs frequency regeneration by analyzing the decoded core signal to detect and attenuate tonal components near transition points, applying cross-over filtering to reduce ringing artifacts, and modifying frequency borders to minimize artifacts during the reconstruction process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If bandwidth extension techniques are used to maintain audio quality at low bitrates, then audio quality is improved, but artifacts like dissonance and beating occur
Solution Approach 1:
The patent applies cross-over filtering to attenuate tonal components near transition points between low-frequency and high-frequency spectral regions. This converts potentially harmful tonal components that cause dissonance and beating into beneficial attenuated components, eliminating artifacts while preserving audio quality at low bitrates
Solution Approach 2:
The patent applies localized attenuation only to tonal components near transition points (cross-over frequencies) rather than uniformly across the entire spectrum. This selective approach maintains audio quality in critical regions while eliminating dissonance and beating artifacts only where they occur, preserving overall perceptual quality
2Adaptability or versatility
If spectral patching is used to reconstruct high-frequency regions, then audio bandwidth is extended, but computational complexity increases
Solution Approach 1:
The patent extracts and removes tonal components from the spectral patches before they are synthesized in the high-frequency region. By taking out the problematic tonal components that would require complex processing to manage, the system simplifies the overall computational complexity while maintaining bandwidth extension capability
Solution Approach 2:
The patent performs preliminary attenuation of tonal components near transition points before the spectral patching and synthesis process. This preliminary action prevents the formation of artifacts that would otherwise require complex post-processing, thereby reducing overall computational complexity
3Productivity
If frequency regeneration is performed without signal analysis, then processing speed is improved, but artifacts like ringing occur
Solution Approach 1:
The patent performs preliminary analysis of the decoded core signal to identify tonal components near transition points before frequency regeneration. This preliminary action allows the system to attenuate problematic components in advance, preventing ringing artifacts without requiring complex post-processing, thus maintaining processing speed
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
Apparatus for decoding an encoded audio signal comprising an encoded core signal and parametric data, comprising: a core decoder (600) for decoding the encoded core signal to obtain a decoded core signal; an analyzer (602) for analyzing the decoded core signal before or after performing a frequency regeneration operation to provide an analysis result (603); and a frequency regenerator (604) for regenerating spectral portions not included in the decoded core signal using a spectral portion of the decoded core signal, the parametric data (605), and the analysis result (603).