Ok, so I'm not a proficient sweep picker, but to maybe help you understand it, I'll give this a shot.
Take any chord, let's say the "open" E major chord with the (root on the low E string).
If you strum all the strings quickly in one motion, it gives the illusion that they all sound simultaneously (obviously this is called a chord), as if you played a chord on the piano. It happens so fast that our ears and minds can't here the separation between the strings.
If you slow the "strum" down enough so that there is a distinct separation between the attack on each individual string, this is a basic arpeggio- a "broken" chord.
When we mostly hear arpeggios, though, the previous note's duration doesn't overlap into the next note, as when we play a scale. To perform this on the guitar you must release the fretting finger, or mute the string, as or before you play the next note. (On a piano, you would start with the thumb, play the note, release it, play the next note with the index finger, release,then middle finger, etc.-- here is where music theorists like to ponder the difference between a scale and an arpeggio-- sometimes it isn't so clearly defined)
If you don't pause your picking hand on it's way over all of the strings as you do this (like when you play a chord), then you've just performed a basic sweep. If you pause over the strings to pick them, or alternate your picking (up, down, up, etc) as you pass over them-- you have not performed a sweep. Of course you can sweep only two or three strings, and then continue on with something else-- you don't have to sweep all six...
It's fairly easy to do a sweep in one direction, but the difficulty in sweep picking is passing back over the strings in the opposite direction without interruption.
In our E major example, after you strike the high E string with your pick on the downstroke, you would then have to
restrike it, or skip over it, to start the sweep back up.
The alternative is to change from the downstroke to an upstroke BEFORE you strike the high E string to start the sweep back up to the low E. Here, after you strike the B string on the downstroke, skip over the E string with the stroke, change the stroke to an upstroke and strike the high E string and back over the B, G, D, A, and low E strings.
We do this all the time when we alternately pick a single string, but it's tricky to do it in the middle of a sweep and skip over a string, because you can't pause to do it! When you through an object in the air, it doesn't pause (at least not for very long, depending on who you ask:), it is either going up or down. Your sweep must also be this way.
Another difficulty is fretting multiple notes on the same string (hammer-ons and pull-off's, aka "slurs") as you do a sweep. Let's say you just started your sweep on the low E-string. You want to play an F# and G# on the low E-string before your pick strikes the A string on its way down. This takes some serious coordination and timing, especially if you do some fretting on each string!
Using the open E major example again, let's say you also wanted to play an F# and G# on the HIGH E string before you came back up again. Here you would likely have to pick the high E string AGAIN to start the upstroke.
Hope this lengthy explanation (or small article) helps, because I'm now sick of thinking about it!
Cheers
chrimsun
Feel free to email me at chrimsun@hotmail.com
