I haven't played guitar since university, and haven't done science since high school, so the particulars of this are lost on me. What I do know, though, is that rigging up a real electric guitar to play Rock Band is awesome.
This isn't a fancy controller made exclusively for Rock Band, it's a real, honest-to-goodness electric guitar, running through a couple of converters that are able to take the notes and signal from the instrument and convert it to something the PlayStation 3 (and Rock Band) can understand.
Rock stars of a technical inclination can grab the necessary code from the link below. Everyone else who just wants to see how it's done, turn your sound up, the volume on the clip is super low.