Double tracking guitar parts has been a technique used in recording for decades (and also live actually, if there is more than one guitarist) to thicken things up. It can make guitars sound bigger, fuller, wider, and more textured. In the '60s Abbey Road Studio's engineer Ken Thousand came up with a way to "automate" that effect on vocals, while working on a record by The Beatles: he called it "Artificial Double Tracking," what today is commonly referred to as "slapback delay" (although at the time, of course, it was done using analog tape).... Click on the title for more