I haven’t looked at Petrucci’s technique in a long time and was stunned what a huge amount of elbow movement he uses in the high speed stuff. I was aware that it can be done that way, but didn’t realize that’s how he does it.
And in this kind of close-mic’d video, even the unamplified sound of the attack is almost a giveaway of how much elbow he uses, because you can hear how forcefully the pick is powering through the string. You can tell he’s either using little or no “edge picking”, a deep pickstroke, or both. In my experience, a very forceful elbow mechanic is the only way to execute that kind of attack with this sort of sound at high speed. Even big forearm rotation with a deep pickstroke doesn’t seem to produce a sound like this, and everything I’ve seen or tried with wrist-only mechanics seems to require a much shallower or more “edge-picked” pickstroke at high speed than we’re hearing here.
Edit: Looking at the clip again, he does seem to be using a significant amoung of leading edge picking, but the sound at, for example, the 35 second mark makes it clear that he has a lot of pick on the string, and the use of elbow in the motion is pretty unmistakeable.
Note that this doesn’t mean he always uses elbow. In the Anderton’s interview posted above, there is lots of rhythm playing and “less crazy fast” lead playing where he sometimes uses forearm rotation, and sometimes uses wrist movement (and sometimes forearm rotation and wrist movement together). But the Facebook video above clearly shows that there is some stuff where he plays certain fast alternate picked things with what looks to be UWPS or 2WPS driven mainly from elbow flexion/extention.
The older video below shows this as well, with the lick starting at 7m20s. Notice how when he demonstrates slowly, it’s wrist only, but when he goes fast, you can see the telltale reciprocating movement of the forearm that shows his elbow is working: