Flatten peaks against a line and leave everything under it alone. A clipper has no attack, release or lookahead, so there is no gain movement to hear: the waveform is simply not allowed past a certain height.
Threshold and ceiling
Threshold, from -24 dB to 0 dB, is how hard the signal is driven into the curve. Lower values push more of the material into the bend, so more of it clips.
Ceiling, from -12 dB to 0 dB, is where the output lands. The two are separate on purpose: threshold decides how much clipping happens, ceiling decides how loud the result is. Setting threshold to -6 dB and ceiling to -0.3 dB drives the signal 6 dB into the curve and then places the flattened result just under full scale.
Character
Soft is a tanh curve. It begins bending well before the threshold, so peaks round off gradually and the harmonics it adds are mostly low-order. It is the least obvious of the three on tonal material.
Cubic stays linear longer and then flattens with a matching gradient at the top. Transients keep more of their shape than they do under soft clipping, and there is still no corner in the curve.
Hard cuts straight across. It preserves the most level and is the most audible, which suits a snare or a kick where the added edge reads as attack.
Clipping before limiting
A clipper and a limiter answer the same question differently, and a loudness chain usually wants both.
Transients are short. A limiter reacting to one has to pull the whole passage down for as long as its release takes, and that movement is what pumping is. A clipper removes the transient itself, in place, without touching the material around it. Taking 2 dB to 3 dB off the peaks with a clipper first typically lets the limiter behind it work far less hard for the same output level.
Mix
Mix blends the clipped signal against the original. At 100% only the clipped path is heard and the ceiling holds. Below that, the untouched signal comes back in and the peaks return with it, so the ceiling stops being a guarantee.
Parallel clipping at 30% to 50% is a way to add the harmonics without losing the transients, but it is not a way to control peaks. Put a limiter after it if the output has to stay under a fixed line.
Example: a drum bus that keeps triggering the limiter
Threshold -5 dB, ceiling -1 dB, character cubic, mix 100%.
The kick and snare peaks flatten by about 4 dB and the body of the kit is untouched, so the limiter behind it stops reaching for 4 dB of gain reduction on every hit.