Soft limiter is the first artifical one, the one you'll feel when you miss a shift at redline and it bangs the engine for a second or two. Example:
vvvvvVVVVVRRRROOOOO-O-O-O-O-O [shift]mmmmm....
Yeah, there's better illustrations. I just don't feel like posting a video.

Greg knows more about this than I do though, so I'm sure he'll chime back in.
-SAV