Always consult the official Owners Manuals first!
Pages A-C are under review. Pages D-Z have been checked and are up-to-date.
Multiband Compressor block
Available on which products
- Axe-Fx III: 2 blocks
- FM3: 1 block
- FM9: 2 blocks
- Axe-Fx II: 2 blocks
- AX8: no
- FX8: no
Channels or X/Y
- Axe-Fx III and FM9 and FM3: 2 channels
- Axe-Fx II: no
About multiband compression
A multiband compressor (MBC) consists of multiple compressors working in parallel, each operating on a separate band of frequencies. Fractal Audio's Multiband Compressor blocks consists of 3 compressors. These compressors work independently, so "pumping" in one band does not affect the others. An MBC is often used as a mastering tool.
In-depth programming of the Multiband Compressor is possible, but even at default settings (placed after Amp/Cab) it's performing fine. 
Or just check the factory preset MULTICOMP PLEXI.