Audio Volume Levelling with Cross-Fade Switching
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Solution Overview
Problem
State-of-the-art volume-levelling (VL) processing technologies introduce audible artefacts when switching between different audio sources due to computational overhead and inefficiencies, particularly when disabling complex filter arrangements for audio data that does not require processing.
Innovation Solution
A method involving a computing device that applies filters to audio data, gradually increasing or decreasing a weighting factor to smoothly phase-in or phase-out volume-levelling processing, using a combination of filters and a delay/gain module, with cross-fading between their outputs to minimize artefacts and reduce computational overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If complex filter arrangements are disabled for audio data that does not require processing, then computational overhead is reduced, but audible artefacts such as timbre shifts are introduced
Solution Approach 1:
The system dynamically adjusts the processing mode based on the characteristics of the audio data. When audio data requires volume levelling, complex filter arrangements are enabled; when it does not, the system transitions to a simple gain arrangement. This dynamic adaptation resolves the contradiction by optimizing computational overhead while maintaining audio quality through context-dependent processing mode selection.
Solution Approach 2:
A cross-fade mechanism is introduced as an intermediary between the complex filter arrangement and the simple gain arrangement. This cross-fade smoothly transitions between the two processing modes, preventing abrupt changes that would cause audible artefacts. The intermediary enables efficient disabling of complex processing while maintaining audio continuity and quality.
2Measurement precision
If filter coefficients are changed in real time on a frame-by-frame basis, then volume levelling accuracy is improved, but computational complexity increases
Solution Approach 1:
The audio processing is segmented into discrete frames, with filter coefficients updated on a frame-by-frame basis. This segmentation allows for precise volume levelling control within each frame while limiting the computational complexity to manageable intervals. The segmented approach enables accurate real-time processing without overwhelming computational demands.
Solution Approach 2:
Filter coefficient updates occur periodically at fixed frame intervals rather than continuously. This periodic action maintains volume levelling accuracy by regularly adjusting coefficients while reducing computational complexity by avoiding continuous updates. The periodic nature of the updates provides a balanced solution between precision and computational load.
3Object-affected harmful factors
If cross-fading is used to transition between processing modes, then audible artefacts are reduced, but processing time increases
Solution Approach 1:
The cross-fade mechanism changes the weighting parameter between the complex filter arrangement and simple gain arrangement over time. By gradually adjusting this parameter rather than making abrupt changes, the system reduces audible artefacts while keeping the processing time extension minimal and acceptable for maintaining audio quality.
Data Source
AI summary
A method in a computing device configured to perform volume-levelling processing on input audio data by at least applying one or more filters to the input audio data, the computing device being configured to obtain an estimated difference between a target output loudness level and a loudness level associated with the input audio data, and to adapt the filter coefficients of the one or more filters based on the estimated difference. The method involves starting, or stopping, the volume-levelling processing. The method comprises gradually increasing, or decreasing, a weighting applied to the estimated difference, in response to obtaining an indication to start, or stop, the volume-levelling processing.