At some point in time you may need to limit audio in your production. Possibly in a multitrack mix you might want to limit the music so it can’t exceed a certain db level. A hard limiter is not normalisation in that it’s function is to place a ceiling on audio. Think of it as a hedge trimmer. You move your trimmer along the hedge at a certain height and anything above the height is cut off but the hedge beneath the trimmer remains untouched.
Adobe Audition has a built in Hard Limiter which has only a few settings to configure.
The Maximum Amplitude is the easiest one to understand. It does as it says and allows now audio to pass the level set here.
Input boost provides a boost to all the remaining audio. Over using this can turn the hard limiter into a compressor by removing all the dynamic range in the audio. Remember the boost you apply here still doesn’t change the fact that no audio can pass above maximum amplitude so a heavy input boost drastically reduces dynamic range and in effect becomes a compressor. This is worth noting if you have compression in your processing chain also.
Lookahead time is how far ahead the hard limiter “reads” the audio to decide when to react.
The release is the same as a compressor and determines how long after the hard limiter has hit audio above the maximum amplitude and cut it off that it then releases its effect.