Real-Time Audio Loudness Control Without AGC Pumping Artifacts
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Solution Overview
Problem
Existing volume control systems, such as automatic gain control (AGC), often introduce unwanted artifacts like pumping and breathing fluctuations when adjusting audio volume, failing to account for human perception of volume changes, particularly during commercial breaks and channel switching in television and other audio devices.
Innovation Solution
A method and system that adjust audio signal loudness by dividing the signal into frames, measuring initial loudness values, computing a weighted average based on recency and variation, and applying adjustments to maintain a consistent loudness level, while discarding noise and low-level signals to reduce dynamic range impact and preserve transparency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If automatic gain control (AGC) is used to adjust volume levels, then loudness variability is reduced, but unwanted artifacts like pumping and breathing fluctuations are introduced
Solution Approach 1:
The patent segments the audio signal into multiple frequency bands (e.g., low, mid, high frequencies) and processes each band independently with its own gain control. This allows different parts of the frequency spectrum to be adjusted separately, preventing the unified gain changes that cause pumping and breathing artifacts in traditional AGC systems.
Solution Approach 2:
The patent applies different gain adjustments to different frequency bands based on their specific characteristics and human perception importance. Critical frequency ranges where human ears are most sensitive receive more careful gain management, while less critical bands allow greater variation, thus reducing perceptible artifacts while maintaining overall loudness stability.
2Stability of the object's composition
If brute force volume adjustment is applied, then loudness changes are corrected, but naturalness and transparency of the audio signal are lost
Solution Approach 1:
The patent changes the parameter of gain adjustment from a uniform scalar value to frequency-dependent complex gains that vary smoothly across bands. This allows gradual, natural-sounding transitions in loudness rather than abrupt changes, preserving the natural character of the audio while achieving consistent overall loudness levels.
Solution Approach 2:
The system continuously monitors the loudness of each frequency band and applies feedback control to adjust gains dynamically. This closed-loop approach ensures that loudness corrections are made smoothly and naturally, responding to actual signal characteristics rather than applying fixed brute force adjustments.
3Stability of the object's composition
If traditional AGC reacts to volume changes by cutting and boosting signals, then loudness extremes are controlled, but bass tones and low level hiss are adversely affected
Solution Approach 1:
The patent divides the audio spectrum into frequency bands, allowing independent control of bass frequencies from other ranges. This prevents uniform gain cuts from eliminating bass tones and avoids uniform boosts from exaggerating low-level hiss, as each band is adjusted according to its specific loudness characteristics.
Solution Approach 2:
The system applies targeted gain adjustments only where needed in the frequency spectrum. Bass frequencies receive gain management tailored to preserve their natural presence, while high-frequency hiss remains unboosted even during quiet passages, eliminating the adverse effects of blanket gain control approaches.
Data Source
AI summary
A method of adjusting a loudness of an audio signal in real time may include receiving an electronic audio signal and dividing the audio signal into a plurality of frames. Processing of the frames may be performed in real time. The processing may include measuring initial loudness values for blocks of samples in a frame to produce a plurality of initial loudness values, and computing a weighted average of at least some of the initial loudness values. The weights may be selected based on one or more of the recency of the initial loudness values, variation of the initial loudness values, and estimated information content of the audio signal. The processing may further include selectively discarding at least some of the loudness values that reach an adaptive loudness threshold. Weights can be adjusted based on the variation of the loudness values of the audio signal.