Tim,
I agree with Robert. Compression is best used with a clean sound. Creates a smooth even level when picking. On the Vox, compression sounds and reacts cool with a lot of the clean models in that the harder you pick the attack is compressed BUT the gain it produced on the attack still manages to come through sweetly. This is typical of a real tube amp when all the tubes react to picking attack as tubes/valves naturally compress in their own beautiful way. I really gotta hand it to the Vox's "Valve Reactor" in this case. What we mean by "even level" when using compression is that the actual volume output should stay about the same. An uncompressed signal would cause a sound meter to peak in the red as you play with an aggressive attack. With compression the sound is usually pretty consistent in output level.
Guitars/Bass - MIM Fender Classic 50s Strat, MIM Fender Standard Strat, Squier Classic Vibe 50s Tele, Gibson Les Paul Studio, Epi '56 Gold Top Les Paul, Martin DSR acoustic, Sigma Martin Auditorium electric/acoustic, Squier Jazz Bass.
Amps/Cabinets/Modelers - Model 2558 50 watt Marshall Silver Anniversary Jubilee combo w/ Celestion Vintage 30s, 4x12 Marshall cabinet w/25 watt Greenback Celestions, Fender Blues Junior w/ a couple of Billm mods, Line 6 POD 2.0, Roland Micro Cube
Pedals/Effects - Cry Baby Classic Wah, Boss TU-2, Boss NS-2, Boss RC-2 Loop Station, Ross Compressor, MXR Micro Amp, Danelectro FAB Echo, Danelectro FAB Chorus, Danelectro Chicken Salad, Marshall Guv'nor Plus, Marshall Echohead, Duhvoodooman's Zonkin' Yellow Screamer, Digitech Digiverb, Digitech Bad Monkey, Dunlop Fuzz Face, Homemade Loop Bypass pedal, Duhvoodooman's Sonic Tonic (Maxon SD-9 clone +), Voodoo Labs Superfuzz