Look Ahead Delay
It may sound a bit exaggerated, but even audio has to follow causality. In consequence every reacting system is too late to fully reduce a signal to a certain value without introducing a high amount of signal distortion. To design a true brickwall limiter or even a fast compressor, it is necessary to introduce delay into the signal path.
The detector circuit receives the input signal in real time, reacts and generates a dynamic gain change. The input path feeding the gain element (the controller) is delayed by 2 milliseconds. Thereby the gain reaction is already taking place, when the original sound appears at the controller. High peaks are reduced entirely with minimal distortion and signal degradation. The only downside is the essential signal latency of 2 milliseconds which is noncritical in most applications.