Audio Spectrum Analysis for Detecting Bandwidth Limitation Artifacts
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Solution Overview
Problem
Existing audio coding technologies, such as MP3 and AAC, introduce artifacts like 'Birdies,' bandwidth limitation, and tonal spikes at low bitrates, degrading audio quality, and there is a need to detect and mitigate these artifacts, especially in signals processed with Spectral Band Replication (SBR) and bandwidth reduction.
Innovation Solution
A method that analyzes the audio signal's spectrum to identify characteristics related to spectral enhancement processing, such as SBR, and artificial bandwidth limitation, using local maximum signals and slope evaluations to determine if post-processing is required, allowing for targeted enhancement to reduce artifacts like 'Birdies' and bandwidth limitation.
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 is reduced and storage efficiency is improved, but coding artifacts (Birdies, bandwidth limitation, tonal spikes) are introduced that degrade audio quality
Solution Approach 1:
The patent detects coding artifacts (Birdies, bandwidth limitation, tonal spikes) introduced by perceptual audio coding and applies post-processing techniques to mitigate them. By identifying the presence and characteristics of these artifacts through spectral analysis, the system converts the harmful effect of compression into a detectable pattern that can be corrected, thereby improving audio quality while maintaining low bitrate.
Solution Approach 2:
The patent performs preliminary detection of coding artifacts during the decoding process before final audio output. By analyzing the spectrum of the decoded signal and identifying characteristic patterns of Birdies, bandwidth limitation, and tonal spikes early in the processing chain, the system can apply appropriate correction measures before the artifacts reach the listener, preventing rather than just treating the quality degradation.
2Object-affected harmful factors
If Spectral Band Replication (SBR) is applied to extend bandwidth at low bitrates, then audio quality is improved, but tonal spike artifacts and beating artifacts are introduced
Solution Approach 1:
The patent detects tonal spike artifacts generated by SBR processing through spectral analysis and applies post-processing to attenuate these spikes. By converting the harmful tonal artifacts into detectable spectral patterns, the system can selectively reduce their amplitude while preserving the beneficial bandwidth extension effect of SBR, thereby transforming the harmful byproduct into a correctable anomaly.
Solution Approach 2:
The patent applies localized correction to specific frequency regions where tonal spikes occur rather than uniformly processing the entire spectrum. By identifying the precise frequency locations of tonal spikes generated by SBR and applying targeted attenuation only to those specific frequency bins, the system preserves the overall quality improvement from bandwidth extension while eliminating only the harmful localized artifacts.
3Quantity of substance
If artificial bandwidth limitation is applied to further reduce bitrate, then compression efficiency is improved, but bandwidth limitation artifacts and muffled sound are introduced
Solution Approach 1:
The patent performs preliminary detection of artificial bandwidth limitation through spectral analysis before final audio rendering. By identifying the characteristic sharp cutoff patterns in the spectrum that indicate artificial bandwidth limitation, the system can apply pre-processing measures such as spectral shaping or noise filling in the attenuated frequency regions before the artifacts become audible, preventing the muffled sound effect while maintaining compression efficiency.
Data Source
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AI summary
An apparatus for determining a predetermined characteristic related to an artificial bandwidth limitation processing of an audio signal comprises a slope evaiuator configured for evaluating a slope of a spectrum of the audio signal to obtain a slope evaluation result. The apparatus comprises a frequency evaiuator configured for evaluating a cut-off frequency of the spectrum of the audio signal to obtain a frequency evaluation result, and comprises a processor for providing an information indicating that the audio signal comprises the predetermined characteristic dependent on an evaluation of the slope evaluation result and an evaluation of the frequency evaluation result.