There are times when you want to focus your dynamics processing on just one part of a signal, say the bass or mid-range. Conventional compressors will affect all frequencies equally. In situations like these, having a good multiband compressor is essential, and FabFilter’s Pro-MB is about as essential as they get.
Where most multiband compressors will provide you with crossover points to isolate frequencies for dynamics processing, Pro-MB instead allows you to insert bands at the appropriate point. Compression can then be applied where and only where you need it.
With additional functionality like expansion (upwards compression), a dynamic phase processing mode that eliminates latency and pre-ringing, and mid/side modes alongside your usual functions like lookahead and soft knee, Pro-MB has most everything you could need in a multiband compressor. The price is a little on the high side but it has to be said, it really does sound great, and the intuitive GUI is the icing on the cake.