What we're looking at here is quite possibly the most powerful dynamics tool known to mankind. There really is very little else in the same ballpark, and the pro-MB is even vastly more powerful than the previous dynamics plugs produced by FF.
I think the major application for the pro-MB is in altering or repairing audio loops and tracks that have been recorded previously - ie where several channels are now irrevocably layered. This could mean spicing up classic drum loops, remastering old "masters", gating or reducing certain instruments in a mix, or replacing one drum sound in an old loop.
The plug appears to be generally promoted as a "multi-band compressor" - however I think it might be more useful to call it an advanced dynamic equalizer. Probably the first thing to note is that this thing does all four varieties of dynamics equally well. Specifically this means: 1) standard compression (reduce above the threshold, raise the output), 2) upward compression (increase below the threshold), 3) transient enhancing (increase above the threshold, lower output) and 4) basic expansion (reduce below threshold). Switching between these modes is done by a comp/exp button and a positive/negative range. It took me a long time to get my head around this and I found I had to write notes about the different modes until it sunk in. These relatively uncommon modes allow you to do things that no other plugs can do. For example, using upward compression you can raise the volume of some background percussion without altering the sounds of other instruments. Basic expansion allows you to vastly reduce certain instruments etc.
The dynamics processing can be tweaked in just about every way you could possibly desire. There is an optional lookahead of up to 20ms, oversampling up to 4x, program dependent attack and release, variable knee shape, optional limiting by range, and variable ratio. There is literally nothing missing in this thing and it's all exceptionally well implemented. It can be transparent even when you are really pushing it. Furthermore there is an extremely useful wet/dry that runs up to 200%, which allows you to create an over-the-top sound and then scale it back to the realms of normality.
On top of these remarkable features the compressor is "multi-band". Therefore radically different compressor settings can be ascribed to various frequency ranges. For example there may be upward compression on the mids, basic expansion on the lows, and transient enhancing on the tops. Each band may also be "side-chained" to a different frequency range, ie when the bass sounds you could chose to raise the top end, and so forth. The dynamics band can also be triggered by an external sidechain (one per instance of the plug). This allows you to potentially insert new sounds into an old piece of audio, ie you could insert a new kick drum sound into the low frequencies.
Another feature (damn there's a heck of a lot) is the stereo processing. Individual bands can be panned (at the gain knob) to either mid or side. Each band can further be set to process only the mid or side by varying amounts. Although the "stereolink" knob is over there near the sidechain section, it actually affects the processing of the band, not merely the triggering. This feature also exists in the FFproC2. It can be confusing the first time you come across it.
The analyzer is very good although I preferred it much faster and more precise than the default. The incoming signal is not exceptionally differentiated from the outgoing - the outgoing has a defined line to the top of it. It takes a while to learn but it can be very useful.
I'm not going to talk about the "dynamic phase" business because I don't entirely understand it. I couldn't get a bad sound out of it. The mechanics are probably not all that important to the end user.
So I have really written a lot here a lot about this plug. I think perhaps it is more powerful than many artists/producers will know what to do with. In many ways it feels "ahead of the game". I think folks are going to discover this and use it to do things that have perhaps never been done before.
Don't think I have ever written such a glowing review. What's going on? :-)
The sound quality, CPU efficiency and interface ergonomics are perfect.
The only strange thing, as to me, is that in Dynamic Phase processing mode (which in fact is dynamic EQ mode) equal damping of adjacent bands result in non-flat amplitude response (significant peak at crossfade freq. is present). Seems, this is not an immanent feature and maybe can be corrected (e.g. using two consequent symmetric low- and hi-shelve filters with same 'significant frequency' result in flat response, even if not it always can be corrected by realative frequency shift).