If I'm not mistaken, Cakewalk advertises the TL-64 Tube Leveler as one of their mastering plugins. Although I know it can be used for other things, I wanted to find out exactly what purpose it serves during mastering?
My guess is that it's supposed to be used as a soft-clip gain reduction tool right before the mastering limiter to clip some of the sound and reduce some gain. In this way, the mastering limiter wouldn't need to fight as much to do all of the gain-reduction, especially with the sharp transient peaks, since the Tube-Leveler reduces some of the gain prior to it.
If my guess is right, what are some of the ways the tube leveler can/should be used for this (e.g. less input + more clipping, versus more input + less clipping)?