What is a limiter?
A limiter is a dynamics effect that keeps signal peaks from going above a ceiling you set. It is similar to a compressor, but it restrains peaks above that ceiling with a far stronger ratio. Units built specifically to let nothing past the ceiling are called brickwall limiters.
Main uses
It is used at the end of the mastering chain to raise the overall level while managing peaks, and to protect later stages from sudden peaks. Ceiling or Output Ceiling sets the output limit, and raising Gain or Input increases Gain Reduction by however much the signal hits that limit.
How it differs from a compressor
A compressor is used to shape level differences and note attacks over a wide range, while a limiter mainly handles the peak ceiling. The line between them overlaps depending on the unit and the settings, but separating them by purpose makes both easier to understand.
Do not push the loudness too far
Heavy limiting raises the average level, but it can also cost you attack and bring out distortion or pumping. It also cannot undo a sound that was already clipped and distorted at the recording stage. Compare before and after at a similar playback level and check that the musical dynamics are still there.
Check True Peak as well
Even when the digital sample values stay under the ceiling, waveform interpolation at playback can push inter-sample peaks above it. True Peak limiters and meters estimate and manage these peaks too. For a final export intended for distribution, one common approach is to leave some headroom rather than pinning the Ceiling right at 0 dBFS.
