I haven't got around to making me a new clean patch since I switched to using studio monitors, but I used to get pretty good results with the USA Clean amp sim with the Parametric EQ after it, mimicking the Mesa "Classic V" eq curve.
Take factory preset #240 (or 241, depending on your offset) "USA Clean", and put a Parametric EQ with these settings between the Amp and the Cab blocks:
Parametric EQ:
F1
Freq. 80.8 Hz
Q. 0.812
Gain. 8.79 dB
Type. Shelving
F2
Freq. 238.8 Hz
Q. 0.707
Gain. (minus) -0.47 dB
F3
Freq. 748.2 Hz
Q. 0.718
Gain. (minus) -7.46 dB
F4
Freq. 2181 Hz
Q. 0.707
Gain. 2.36 dB
F5
Freq. 6618 Hz
Q. 0.707
Gain. 0.00 dB
Type. Shelving
These are my Para EQ settings for my Mark IV patch, but since the USA Clean amp sim is basically the clean channel on a Mark IV/Triaxis and I'm sure Petrucci has the Mesa's on-board graphic eq engaged on his clean tone as well has his dirty tone, it's part of that type of clean sound.
I just tried it and it's in the ballpark. It was a little dark. I would raise the Presence on the amp sim and/or the unused 6618 Hz freq on the Parametric EQ to add more of that glassy high end sparkle. You also might raise the Amp sim's Depth control some to get a little more of a deeper bass (if you want it - the clean tone on "Metropolis Pt.1" sounds fairly devoid of bass). You might also change the cab sim to one of the Mesas (Recto 1&2, Cali 4x12) since those are the types of cabs JP plays through.
Good luck. Let me know what you come up with.
EDIT - One unconventional thing you might try is removing the Cab block altogether. This sounds terrible on dirty tones, but kind of cool on clean ones. It kind of gives it that airy, glassy sound Petrucci had on " Images & Words". If that is too much, you might run a separate row of shunts from the Parametric EQ, but before the cab block, to the Output. This way you'll have 2 signals (one with a cab sim, one without) that you can blend them together with however much of one or the other you want.
Damn, now I want to start working on a good Petrucci clean tone. :mrgreen:
EDIT #2 (No, shredi never sleeps. :twisted: ) A big part of Petrucci's clean tone is that his pickups are wired so that when his selector switch is set to the middle position, it splits the coils and only the 2 inner ones of his bridge & neck humbuckers are active. This give a very unique sound that is one of the keys to his clean tone (my Carvin is wired to do the same thing). But being the Petrucci freak you are, you probably already knew that.
