I assume this is some sort of polyrhythm but my brain refuses to be able to count it. Can someone shed some light on whats going on?
The song in question:
Music: Practice & Theory Stack Exchange is a question and answer site for musicians, students, and enthusiasts. It only takes a minute to sign up.Sign up to join this community
The beat of the track is a straightforward 4/4, with chord changes and drum loop repeats every bar of 16 sixteenth notes. However, the synth riff or bass line that begins around 0'31" and sounds like a Roland TB-303, repeats after 9 sixteenth notes.
Therefore the bass line shifts around relative to the beat; the note that plays on the first beat will come a sixteenth note after the third beat, and then 2 sixteenth notes after the first beat of the next bar, and so on... After four and a half bars (i.e. 18 beats) the same note in the bass line will be back on the first beat.
So it's not a polyrhythm as such, just several repeated elements of different length sounding together. You'll hear this technique often in electronic pop music, because it's easy to create and interesting to listen to, and makes the listener pay attention.
Its use is not limited to electronic music, of course; e.g. it's the basic idea behind Steve Reich's Violin Phase from 1967.