The Mechanics of Sweep-Picking
Sweep-picking is a technique that allows you to play arpeggios at a very rapid rate. As you know, normal picking entails up and down, or alternate, picking. You also know that, normally, arpeggios contain only one note per string, and move up and down the fret board very quickly. If you ever tried it, you know that trying to alternate-pick only one note per string is a real challenge. Some very smart guitar player looked at the problem and said, “Why can't I just pick it all in one direction?” Instead of alternating your pick strokes up and down, let your pick glide, or “sweep,” in one direction using gravity to move your pick through the strings.
This is a much more efficient way to pick arpeggios, and as a result you can really hit the gas pedal with this technique. But it's not just for fast players; the technique is so efficient that you may find yourself doing it on examples other than arpeggios. This technique may have stemmed from a violin technique. Violinists drag their bow in fast passages because it's inefficient to bow up and down.
There are more sloppy sweep-pickers in the world than you can imagine, and this is because there's a shortage of solid instruction on how to sweep beyond just “gliding the pick.” Four main factors go into sweep-picking: