As a concept, I'm a fan of multiband compressors and expanders. Being able to compress and/or expand precise frequencies is incredibly powerful. However, it's easy to make a mix much worse if you make the wrong choices or use a multiband compressor/expander that introduces things such as phase problems or artifacts. FabFilter's Pro-MB won't magically prevent you from making bad choices and ruining a mix, but it can help you to gain some of the benefits of multiband compression/expansion while minimizing the chances you will introduce problems. Because of it's excellent interface, intuitive and responsive controls, a wealth of helpful information on all of its features and high-quality processing, Pro-MB is definitely a plugin that deserves to be on your short list if you're looking for a multiband dynamics processor for your workflow.
As with FabFilter's superb Pro-Q plugin, Pro-MB's controls are smartly designed and a joy to use. When you don't need them, they are out of your way. Click on a band and controls are immediately displayed. Knobs and switches are responsive. You can drag knobs to change Pro-MB settings, but for more precise control, you can use the scroll wheel on your mouse for buttery-smooth adjustments. Tooltips appear to show you the precise value for the control you're altering.
The flexibility of Pro-MB's approach means that you don't have to worry about complex crossover configuration at band boundaries. When you add bands to Pro-MB, any frequency range that your bands don't encompass is entirely unaffected. If you choose, you can have your bands snap right up against each other, but it's not required. Pro-MB's approach to multiband compression and expansion is unique and quite flexible, and after using Pro-MB for a short while, we're convinced that this is the best design for this kind of work.
Just as with FabFilter's other plugins, context-sensitive help is available by simply hovering over a control. If you want additional help, it's a click away via the Help menu. FabFilter also reveals plenty of tips and tricks on their YouTube channel. We find FabFilter's YouTube videos to be an excellent way to get the most from FabFilter plugins.
Side-chain filtering isn't unique to Pro-MB, but the ease at which you can use this powerful capability is.
Another area where Pro-MB takes a different approach is in side-chain filtering. The side-chain is the signal that the compressor/expander is "listening" to in order to do what it does. By adjusting what the side-chain is listening to, you can do things that would otherwise be very difficult or impossible. For example, you can add some compression to the low end and use side-chain filtering to ensure that the compressor doesn't take off the punch from your bass drum. You can also use side-chain filtering to do things like duck guitar frequencies that conflict with vocal frequencies.
Side-chain filtering isn't unique to Pro-MB, but the ease at which you can use this powerful capability is. By default, Pro-MB uses the band's own signal to trigger the side-chain, but you can click the Free button to display a filtering control (shown as a blue line over the "Band" button in the figure below) that lets you quickly and easily set the high- and low-pass frequencies at which side-chain filtering is triggered.
FabFilter says that Dynamic processing mode uses "clever dynamic filtering" to achieve its result. We feel that they're just being modest because in our opinion, Dynamic processing is nothing short of genius.
FabFilter has also solved another problem often encountered with multi-band dynamics processing; the introduction of phase shifting or pre-ringing artifacts. Pro-MB offers three different processing modes: Linear, Dynamic, and Minimum. Minimum mode provides near zero latency, but it introduces some pretty extreme phase shifts at crossover points. You can work around that by using Linear mode, but in doing so, you introduce not only latency, but also the possibility of pre-ringing artifacts. The near-perfect solution to both of these problems is Pro-MB's Dynamic processing mode.
When you use Dynamic processing mode, no latency is introduced, and phase shifting is minor based upon how much processing you perform. Even with fairly strong processing, phase shifting is minimal and likely not to cause you any concern. FabFilter says that Dynamic processing mode uses "clever dynamic filtering" to achieve its result. We feel that they're just being modest because in our opinion, Dynamic processing is nothing short of genius and it makes us entirely comfortable using multi-band dynamics processing in situations where we would have never done so before.
There are far too many other great features to name them all, but FabFilter offers a full 30-day trial of all of their plugins so that you can try them out for yourself. They offer plugins for both Windows and Mac (32-bit and 64-bit) and they support VST, VST3, Audio Units, AAX Native and AudioSuite formats. You can also get them in RTAS, but only in 32-bit.