Audio Loudness Control Using Spectral Localization Adjustment
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Solution Overview
Problem
Existing audio signal processing technologies overrate spectrally localized signals in loudness measurements, leading to disproportionate gain changes and potential annoyance in audio mixing, particularly during vocal singing.
Innovation Solution
A method that estimates spectral localization of an audio signal by determining the energy distribution across frequency bands and adjusts the broadband loudness measure using a scaling factor, which is then temporally smoothed to modify the audio signal's loudness, ensuring more accurate subjective loudness representation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing audio signal processing technologies measure loudness using broadband level, then the loudness measurement is simple to compute, but spectrally localized signals are overrated leading to disproportionate gain changes
Solution Approach 1:
The audio spectrum is divided into multiple frequency bands (e.g., 5 bands based on perceptual frequency banding scale) to analyze spectral distribution. This segmentation allows the system to detect whether signal energy is concentrated in specific bands, enabling accurate identification of spectrally localized signals without excessive computational complexity.
Solution Approach 2:
The patent introduces a spectral localization parameter (scaling factor) that modifies the broadband loudness measurement based on spectral distribution characteristics. When signals are detected as spectrally localized (majority of energy within half the total bandwidth), the scaling factor adjusts the loudness measurement downward to prevent overrating, thereby improving measurement accuracy.
2Ease of operation
If gain changes are applied to adjust loudness, then the loudness of the audio signal can be controlled, but spectrally localized signals experience disproportionate gain changes causing annoyance
Solution Approach 1:
The system uses feedback by continuously monitoring the spectral distribution of the audio signal and dynamically adjusting the scaling factor applied to broadband loudness measurements. This feedback mechanism ensures that gain changes are proportional to actual perceived loudness, preventing excessive gain reduction on spectrally localized vocal signals and thereby reducing listener annoyance.
3Productivity
If broadband loudness measurement is used without spectral localization adjustment, then the processing is computationally efficient, but the subjective loudness representation is inaccurate
Solution Approach 1:
The audio signal is divided into a limited number of frequency bands (e.g., 5 perceptual bands) rather than analyzing the entire spectrum continuously. This segmented approach maintains computational efficiency while providing sufficient information to detect spectral localization and adjust loudness measurements accordingly.
Solution Approach 2:
A scaling factor parameter is introduced that modifies the broadband loudness measurement based on spectral localization detection. This parameter change allows the system to accurately represent subjective loudness by accounting for spectral distribution characteristics without requiring complex processing algorithms.
Data Source
AI summary
The invention relates to modifying the loudness of an audio signal by measuring the weighted broadband level of the audio signal and modifying that weighted broadband level as a function of a spectral localization estimate of the audio signal.