FCP X Limiter Filter
What the Limiter filter does – on an instant-by-instant basis – is raise the level of that instant of the clip by an amount you specify, provided the audio level doesn’t go over a maximum limit that you also specify. Audio gain that attempts to go over your limit is thrown-away.
The three key settings in the Limiter filter are: Gain, Gain Reduction, and Output Level. Find out more…