Audio Loudness Control with Noise Classification and Drop Detection

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Solution Overview

Problem

Existing loudness control systems fail to distinguish between desired content and unwanted noise, leading to undesirable amplification of background noise and fluctuations in signal-to-noise ratio, and struggle to maintain uniform average loudness levels without adversely affecting short-term signal dynamics.

Innovation Solution

A loudness control system that includes modules for content-versus-noise classification, temporal smoothing, and gain correction, using frequency domain or time domain noise detection to adjust smoothing factors and apply time-varying gains, while also detecting loudness drops to minimize artifacts during transitions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a loudness control system amplifies all low-level audio content above a predetermined threshold, then the average loudness level is normalized, but the signal-to-noise ratio deteriorates due to unwanted noise amplification

Engineering Contradiction:

Improveloudness normalization precisionVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent segments the audio signal processing into distinct functional modules: a noise detection module that identifies unwanted noise components, a content-versus-noise classification module that distinguishes desired content from noise, and a gain correction module that applies differential gain. This segmentation allows the system to treat noise and content differently, normalizing loudness while preserving signal-to-noise ratio by preventing noise amplification.

Inventive Principle:

Principle #1Segmentation

2Manufacturing precision

If the loudness control system reacts quickly to loudness changes, then the target loudness level is consistently achieved, but short-term signal dynamics are reduced

Engineering Contradiction:

Improveloudness level control precisionVSAvoidshort-term signal dynamics

Core Design Contradiction:

Manufacturing precisionVSDuration of action of moving object

Solution Approach 1:

The patent implements dynamic smoothing factors that adapt based on the detected signal type. During content segments, the system uses smoothing factors that preserve short-term dynamics while maintaining loudness control. During noise segments, different smoothing factors are applied to prevent noise amplification. This dynamic adjustment allows the system to respond appropriately to loudness changes without unnecessarily compressing signal dynamics.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the parameter of the smoothing factor based on the content-versus-noise classification. When noise is detected, the smoothing factor is adjusted to prevent rapid gain changes that would amplify noise. When content is detected, the smoothing factor allows for more responsive gain adjustment. This parameter change enables the system to maintain loudness control precision while preserving signal dynamics during content playback.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If a single smoothing factor is used for loudness control, then the system is simple to implement, but it cannot effectively address both inter-content loudness transitions and intra-content signal dynamics

Engineering Contradiction:

Improvesystem structure complexityVSAvoidloudness control adaptability

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent introduces dynamic smoothing factors that are adjusted based on the operational context detected by the content-versus-noise classification module. During inter-content transitions, the smoothing factor is optimized for rapid loudness normalization. During intra-content playback, the smoothing factor is adjusted to preserve signal dynamics. This dynamic approach provides adaptability without requiring completely separate systems for different scenarios.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system applies different smoothing factor characteristics to different temporal regions of the audio signal based on local signal characteristics. When noise is locally detected, noise-appropriate smoothing is applied. When content is locally detected, content-appropriate smoothing is applied. This local quality approach allows the system to be adaptable to different situations while maintaining a unified overall structure.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS10374564B2Loudness control with noise detection and loudness drop detection

Publication Date: 2019.08.06 DTS INC(US)

AI summary

Loudness control systems or methods may normalize audio signals to a predetermined loudness level. If the audio signal includes moderate background noise, then the background noise may also be normalized to the target loudness level. Noise signals may be detected using content-versus-noise classification, and a loudness control system or method may be adjusted based on the detection of noise. Noise signals may be detected by signal analysis in the frequency domain or in the time domain. Loudness control systems may also produce undesirable audio effects when content shifts from a high overall loudness level to a lower overall loudness level. Such loudness drops may be detected, and the loudness control system may be adjusted to minimize the undesirable effects during the transition between loudness levels.