Audio Peak Limiting with Ratio-History Gain Smoothing
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Solution Overview
Problem
Existing audio peak limiting technologies face challenges in balancing latency and gain smoothing, particularly when dealing with audio signals containing significant low-frequency components, as longer buffers introduce high latency while shorter buffers fail to sufficiently smooth gains.
Innovation Solution
An audio peak limiter apparatus that calculates a smoothed sequence of gains and implements a replacement gain mechanism, allowing for immediate changes during 'attack' and gradual changes during 'release', using a 'history of ratios' to smooth abrupt gain changes over a longer period, thereby maintaining a small buffer size while ensuring sufficient gain smoothing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the buffer length is increased to smooth gain changes, then gain smoothing is improved, but latency increases
Solution Approach 1:
The patent divides the gain control into two separate components: a slow gain component that provides smooth gain changes over time, and a fast gain component that provides immediate response to peaks. This segmentation allows each component to operate with different buffer requirements - the slow gain can use a longer buffer for smoothing while the fast gain uses a short buffer for low latency response.
Solution Approach 2:
The patent introduces an intermediary mechanism where the slow gain and fast gain work together through a combined gain calculation. The slow gain acts as a mediator that smooths overall gain changes, while the fast gain intervenes to provide immediate correction when peaks are detected, resolving the contradiction between smoothing and latency.
2Loss of time
If the buffer length is decreased to reduce latency, then latency is reduced, but gain smoothing deteriorates
Solution Approach 1:
By segmenting the gain control into slow and fast components with different buffer lengths, the system can use a short buffer for the fast gain component to minimize latency, while the slow gain component compensates for smoothing requirements through its own temporal averaging mechanism.
Solution Approach 2:
The patent changes the temporal parameters of gain application by introducing two distinct time scales: a slow time constant for overall gain smoothing and a fast time constant for peak correction. This allows the system to achieve both low latency (through fast gain with short buffer) and good smoothing (through slow gain with longer effective time constant).
Data Source
AI summary
An audio peak limiter apparatus which calculates a smoothed sequence of gains for application to a sequence of blocks of samples of an audio signal. The apparatus sometimes calculates a candidate gain, to replace a too-large smoothed gain, such that applying the candidate gain would produce no scaled sample whose magnitude exceeds a predetermined limit. The apparatus sometimes calculates and stores a final gain to replace the too-large smoothed gain (where the final gain can be obtained e.g. by dividing the to-be-replaced smoothed gain by a prior smoothed gain and multiplying the result by the corresponding prior final gain), if it is determined that the candidate gain is not less than the immediately previous final gain.