Audio Loudness Leveling With Short- and Long-Term Gain Control
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Solution Overview
Problem
Existing loudness leveling methods in audio signals often result in audible artifacts and fail to maintain consistent loudness over longer terms, particularly in broadcast television, where short-term adjustments optimized for minimizing artifacts do not align with longer-term measurement standards.
Innovation Solution
A system and method that includes a short-term loudness leveling module to remove artifacts, a long-term loudness leveling module to measure actual loudness, and a loudness-to-gain module to calculate and apply a gain value, ensuring the audio signal's long-term loudness matches a desired standard without introducing new artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compressor and limiter methods are used for loudness leveling, then short-term loudness fluctuations can be adjusted, but audible artifacts such as breathing or pumping occur
Solution Approach 1:
The patent segments the audio signal into multiple frequency bands and processes each band separately with different attack and release times. This allows short-term fluctuations to be controlled without affecting the entire spectrum uniformly, thereby reducing audible artifacts like breathing and pumping while maintaining loudness leveling effectiveness.
Solution Approach 2:
The patent implements dynamic attack and release time constants that vary across different frequency bands. By making the compression parameters dynamic rather than static, the system can respond appropriately to different types of audio content in different frequency ranges, minimizing artifacts while maintaining control over loudness variations.
2Reliability
If gain adjustment is applied to the whole audio signal, then loudness can be controlled, but audible artifacts such as breathing or pumping occur
Solution Approach 1:
The patent applies different compression characteristics to different frequency bands rather than applying a uniform gain adjustment to the entire audio signal. Each frequency band receives localized processing with tailored attack and release times, which prevents the global gain changes that cause breathing and pumping artifacts while maintaining effective loudness control.
3Speed
If short integration time is used in loudness measurement, then short term fluctuations can be measured faster, but long-term average loudness is less affected
Solution Approach 1:
The patent uses multiple integration times segmented by frequency band rather than a single integration time for the entire signal. Short integration times are used for high-frequency transients to capture fast fluctuations, while longer integration times are used for low-frequency content to accurately measure long-term average loudness. This segmented approach allows simultaneous optimization of both measurement speed and precision.
Solution Approach 2:
The patent implements dynamic integration time constants that adapt to the temporal characteristics of different frequency bands. This allows the measurement system to respond quickly to short-term fluctuations in high frequencies while maintaining accurate long-term averaging in low frequencies, effectively resolving the contradiction between measurement speed and precision.
Data Source
AI summary
Systems and methods for leveling loudness variation in an audio signal are described. Embodiments use both a perceptual leveling algorithm and a standards-based loudness measure together to minimize audio process artifacts and ensure that the measured loudness of the processed audio is close to a required measure, according to a particular standard measurement of loudness. These systems and methods can be used either offline or in real-time.