Audio Spectrum Analysis for Detecting SBR and Bandwidth Artifacts
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Solution Overview
Problem
Existing audio coding technologies, such as MP3 and AAC, introduce artifacts like 'Birdies,' bandwidth limitation, tonal spike, and beating at low bitrates, degrading sound quality, and there is a need to detect and reduce these artifacts, particularly the effects of Spectral Band Replication (SBR) and bandwidth reduction.
Innovation Solution
A method involving a processor that analyzes the audio signal's spectrum to identify local maxima and similarities, determining if spectral enhancement or bandwidth limitation processing has occurred, allowing for targeted post-processing to reduce artifacts without requiring side information, and enabling bandwidth extension tailored to specific signal characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If perceptual audio coding methods (MP3, AAC) are used to compress audio signals, then bitrate efficiency is improved, but coding artifacts (Birdies, bandwidth limitation, tonal spike, beating) are introduced that degrade sound quality
Solution Approach 1:
The patent detects coding artifacts (Birdies, bandwidth limitation, tonal spike, beating) introduced by perceptual audio coding and applies post-processing to suppress them. By identifying the presence and type of artifacts through spectral analysis and applying targeted correction algorithms, the system converts the harmful effects of lossy coding into acceptable quality, enabling bitrate efficiency while maintaining sound quality.
2Quantity of substance
If Spectral Band Replication (SBR) is applied to extend bandwidth at low bitrates, then bandwidth efficiency is improved, but tonal spike and beating artifacts are introduced
Solution Approach 1:
The patent detects tonal spike and beating artifacts specifically caused by SBR processing through spectral analysis and applies post-processing to suppress these artifacts. By identifying the characteristic patterns of SBR-induced artifacts and applying targeted correction, the system maintains bandwidth efficiency while eliminating the harmful tonal and beating effects.
3Quantity of substance
If static low-pass filtering is applied to limit audio bandwidth at low bitrates, then bitrate efficiency is improved, but sound quality deteriorates due to dull and muffled sound impression
Solution Approach 1:
The patent detects bandwidth limitation artifacts through spectral analysis and applies post-processing to restore the natural sound. By identifying the characteristic spectral cutoff patterns and applying appropriate restoration algorithms, the system recovers the high-frequency content that was artificially limited, converting the dull and muffled sound back to natural-sounding audio while maintaining bitrate efficiency.
4Quantity of substance
If coarse quantization is applied to spectral lines at low bitrate, then bitrate efficiency is improved, but Birdies artifact is introduced due to temporal modulation
Solution Approach 1:
The patent detects Birdies artifacts through spectral analysis by identifying the characteristic temporal modulation patterns caused by coarse quantization. By detecting these artifacts and applying post-processing to suppress the modulation effects, the system recovers natural spectral behavior while maintaining the bitrate efficiency benefits of coarse quantization.
5Object-generated harmful factors
If post-processing to reduce artifacts is applied, then sound quality is improved, but computational complexity increases
Solution Approach 1:
The patent segments the audio processing into distinct stages: artifact detection through spectral analysis, classification of artifact types (Birdies, bandwidth limitation, tonal spike, beating), and application of targeted post-processing algorithms. This segmentation allows the system to apply only the necessary processing for each detected artifact type, reducing overall computational complexity compared to applying all processing unconditionally.
Solution Approach 2:
The patent applies post-processing selectively based on the detected presence and type of artifacts. Rather than applying full processing to all audio signals, the system performs partial processing only where and when artifacts are detected, reducing unnecessary computational complexity while maintaining sound quality improvement where needed.
Data Source
AI summary
An apparatus for determining a predetermined characteristic related to a spectral enhancement processing of an audio signal includes a deriver configured for obtaining a spectrum of the audio signal and for deriving a local maximum signal from the spectrum. The apparatus includes a determiner configured for determining a similarity between segments of the local maximum signal and includes a processor for providing an information indicating that the audio signal includes the predetermined characteristic dependent on an evaluation of the similarity.