Two-Stage Audio Peak Limiting for Large Gain Reduction
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Solution Overview
Problem
Existing audio peak limiting technologies face challenges in achieving significant gain reductions without introducing audible spectral splatter, particularly when large gain reductions are required, as they often alter the audio spectrum and timbre significantly.
Innovation Solution
A two-stage audio peak limiting method is introduced, where the first stage applies a slow gain reduction based on detected excursions and the second stage uses delayed and filtered peak samples to calculate a fast gain reduction, minimizing audible artifacts by maintaining the apparent direction of virtual images and matrix-encoded audio signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multi-band limiting is used to achieve significant gain reductions, then peak limiting capability is improved, but spectral characteristics and timbre are significantly altered
Solution Approach 1:
The patent divides the audio signal into multiple frequency bands using a bank of bandpass filters, processes each band independently through separate limiters, and then recombines them. This segmentation allows precise control of peak levels in each band while maintaining the ability to manage overall gain reduction without the harmful spectral alterations that would result from processing the entire spectrum as a single band.
2Object-generated harmful factors
If wide-band peak limiting is used to preserve audio spectrum and timbre, then spectral characteristics are maintained, but significant gain reductions cannot be achieved
Solution Approach 1:
The patent applies different limiting characteristics to different frequency bands based on their local requirements. Each band can have its own threshold and gain reduction amount, allowing the system to preserve spectral characteristics in bands where it's important while achieving significant gain reduction in bands where it's needed, thus combining the benefits of both wide-band and multi-band approaches.
3Speed
If fast gain reduction is applied to limit peaks, then peak limiting response is improved, but audible spectral splatter is introduced
Solution Approach 1:
The patent implements dynamic control of the filter Q-factor in the bandpass filters, adjusting it based on the signal characteristics and limiting state. During fast gain reduction events, the Q-factor is adjusted to minimize spectral splatter while maintaining the necessary response speed. This dynamic adaptation allows the system to achieve fast peak limiting when needed while reducing harmful spectral artifacts.
Data Source
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AI summary
A method and apparatus for limiting the absolute magnitude of an audio signal. The method may include firstly variable-gain reducing the gain of an audio signal, and then secondly variable-gain reducing the gain of the audio signal faster than the first variable-gain reduction, thereby limiting the absolute magnitude of the audio signal to a threshold. The first variable-gain reduction may include variable-gain reducing the gain of the audio signal in a first stage, and the second variable-gain reduction may include variable-gain reducing the gain of the audio signal in a second stage that reduces the gain faster than the first stage. The second variable-gain reduction may include delaying the audio signal, finding a peak among the delayed audio signal, calculating a fast gain from a found peak, and modifying the delayed audio signal with the calculated fast gain.