The intro chord is three identical samples of a clean guitar picking an Am triad chord. The 1st panned slightly to the left, the 2nd is in the middle and is reversed and finally, slightly to the right, the riff ends a 1/4 bar early and very slightly delayed. This gives a four bar variation, it's loosely based on a technique called "phasing patterns" which I learnt about in an episode of the South bank show a while back about a composer called Steve Reich. The main drums are a pattern taken
en-us