Audio Spectrum Analysis for Detecting Artificial Bandwidth Limitation
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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
An apparatus and method that evaluate the slope of an audio signal's spectrum to identify characteristics indicative of artificial bandwidth limitation and spectral enhancement processing, allowing for post-processing to reduce artifacts like 'Birdies' and bandwidth limitation, and differentiate between naturally bandwidth-limited signals and those artificially processed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lossy coding operations like perceptually adapted quantization or parametric coding techniques are applied at low bitrates, then the available bitrate is reduced, but coding artifacts such as bandwidth limitation, Birdies, tonal spike, and beating are introduced degrading sound quality
Solution Approach 1:
The patent detects coding artifacts (bandwidth limitation, Birdies, tonal spike, beating) introduced by lossy coding at low bitrates and applies post-processing techniques to mitigate these artifacts. By identifying the presence of specific artifacts through spectral analysis and applying targeted correction methods, the system converts the harmful effect of artifact introduction into a benefit where artifacts are detected and corrected, improving perceived sound quality despite low bitrate conditions
Solution Approach 2:
The patent changes processing parameters based on detected artifact types. When artifacts are detected through spectral analysis, the system adjusts post-processing parameters to specifically address the identified artifact characteristics, such as applying different filtering or spectral manipulation techniques depending on whether bandwidth limitation, Birdies, tonal spike, or beating artifacts are present
2Quantity of substance
If static low-pass filtering is applied to limit audio bandwidth at low bitrate conditions, then the bitrate requirement is reduced, but the sound quality becomes dull and muffled
Solution Approach 1:
The patent replaces static low-pass filtering with dynamic post-processing that adapts to the detected artifact characteristics. Instead of applying a fixed bandwidth limitation, the system dynamically analyzes the decoded audio signal to detect specific artifact patterns and applies targeted mitigation techniques that preserve more of the original sound quality while still operating within low bitrate constraints
Solution Approach 2:
The patent converts the harmful dull and muffled sound caused by static low-pass filtering into a benefit by detecting the bandwidth limitation artifact and applying post-processing techniques that restore perceived high-frequency content and improve sound quality while maintaining the low bitrate advantage
3Object-affected harmful factors
If Spectral Band Replication is applied to extend bandwidth, then the perceived sound quality is improved, but tonal spike and beating artifacts are introduced when tonal-to-noise ratio is overestimated
Solution Approach 1:
The patent implements feedback by detecting tonal spike and beating artifacts in the decoded audio signal and using this detection information to adjust post-processing parameters. The system continuously monitors for these specific artifact patterns and modifies its mitigation strategy based on the detected artifact presence and characteristics, creating a closed-loop system that adapts to the actual audio content
Solution Approach 2:
The patent changes post-processing parameters based on detected artifact types. When tonal spike artifacts are detected, the system adjusts spectral manipulation parameters to reduce the excessive energy in tonal components. When beating artifacts are detected, the system modifies processing to reduce roughness perception, thereby adapting the processing to the specific artifact conditions
4Quantity of substance
If quantizers are set to very coarse precision at low bitrate transform coding, then the bitrate is reduced, but spectral lines toggle between 0 and 1 introducing Birdies artifact
Solution Approach 1:
The patent converts the harmful Birdies artifact caused by coarse quantization into a benefit by detecting the specific temporal modulation pattern characteristic of Birdies and applying post-processing techniques that suppress this artifact while preserving the low bitrate advantage. The detection mechanism identifies the toggling spectral lines pattern and targets it for mitigation
Data Source
AI summary
An apparatus for determining a predetermined characteristic related to an artificial bandwidth limitation processing of an audio signal has a slope evaluator configured for evaluating a slope of a spectrum of the audio signal to obtain a slope evaluation result. The apparatus has a frequency evaluator configured for evaluating a cut-off frequency of the spectrum of the audio signal to obtain a frequency evaluation result, and has a processor for providing an information indicating that the audio signal has the predetermined characteristic dependent on an evaluation of the slope evaluation result and an evaluation of the frequency evaluation result.