The IK Multimedia Classic T-RackS MultiBand Limiter is three-band peak limiter that makes mixes louder by reducing unwanted peaks.
The peak limiting action is performed separately on three separate bands (low, mid, high) whose width can be set by adjusting the two crossover frequency controls. Each of the three bands has separate controls (threshold and level) to tailor the limiting action as precise as needed by the program material it's used on. Input drive and time constant controls are common to the three bands.
You will have a very loud master, without clipping, though as with any of these processors, use care and not to over-do it. Leaving the output knob set to 0 dB means that the limiter output signal can't go beyond -0.05 dBfs.
This kind of limiter is particularly useful to control audio material where processing needs to be applied only in certain spots, or where an EQ wouldn't fit, being not dynamic (such as in live recorded material where frequency content may drastically change over time). By carefully setting each band's threshold and level the limiting action will only take place when a selected band's level goes beyond the set threshold allowing for very powerful frequency conscious dynamics control.