Stewie, I've been playing guitar for years and still don't know what economy picking is. Can anyone help me out with that?
Pretty much what Siddhartha said, in short. To elaborate a little more on that - it's a form of sweep picking, where you use the momentum of the pick to "follow through" into the next string. Some people also refer to it as "directional-based picking", meaning; the direction in which you pick (whether down or up) is determined by the direction in which you are heading. So, if you are on a lower string and on your way to a higher string, you follow thru with a down stroke, as Siddhartha put it. If you are on a higher string on your way to a lower string, you follow thru with an up stroke.
It is very important, however, to note that economy picking really only works if we are dealing with
odd numbers. Many people will refer to the "three notes per string" scale format to use economy picking, which is fine, however the actual science behind it is based on the odd number of
plucks per string - not necessarily notes (because you could hold one note with your fretting hand and pick it three times, as opposed to picking three separate notes).
With strict alternate picking, a problem is encountered with "three notes per string" scale shapes. Because, you have to change picking direction and hop over the string to get to the next. So, lets say you start on the low E string and pick down-up-down; that puts your pick right between the low E and A strings, at which point you have to hop over the A string in order to pick up, to continue your pattern (since you left off on a down stroke on the low E). When you pick the A string, you pick up-down-up (opposite of how you started your pattern), and leave off on an up stroke. This means your pick is moving
away from the A string, at which point you have to hop back over the A string, in order to get to the D string to continue your pattern. So, in a sense, you're working against yourself - constantly breaking the flow of the direction of your pick.
For this reason, the use of strict alternate picking with odd groups can be a nightmare for some. Obviously players like Petrucci, Steve Morse, Al Di Meola, Paul Gilbert - they have it down. For others, no matter how much time is spent practicing to a metronome, it simply is unnatural. Players like Yngwie Malmsteen, Frank Gambale, Zakk Wylde - they still pick a lot - the difference is, they use economy picking as a means to flow from one string right into the next, without having to change picking directions. Hence the term "economy picking". It's more economic, and you don't to move as much. That's why if you study Yngwie's picking hand closely, you'll notice that it barely moves.
Now, if we're dealing with even numbers, strict alternate picking is a breeze, simply because you never have to change picking directions as you transition from one string to the next. It's just 'down-up-down-up' (or vice versa), and so on and so forth. I myself use a mixture of alternate and economy picking, and have been doing it for so long that I don't necessarily consciously think about it; at this point I switch back and forth, and it's pretty natural for me.
When I first started using economy picking, however, it definitely took some getting used to. It's definitely a challenge to control the rate at which your pick rakes thru the strings, and to make sure that it is synced up with your fretting hand. But, as with anything, with enough time and practice, you can get it to be pretty smooth and seamless. Also, if you like playing fast, you can achieve tempos with the use of economy picking that are very rarely possible to pull off with strict alternate picking.
All in all, I'm not saying it's a better technique, but it certainly is efficient. It's pretty smooth and slick sounding, so if you want that crisp percussive attack, probably should use alternate picking instead.
Lastly, it's a very common technique among jazz players. Guys like Joe Pass, George Benson, Bireli Lagrene, Pat Metheny, Mike Stern - all great examples of economy pickers.
EDIT: Forgot to add that, aside from odd groups, it also only works when dealing with adjacent strings. It doesn't help with string-skipping, which is why it's still really important to practice your alternate picking