Steve Reich is a composer famous for his experimentation with musical looping and phasing. Check this out:
“Steve Reich is calling” Ringtone Phasing like Steve Reich with Apple’s Marimba Ringtone.
The above (by Seth Kranzler) is based on Steve Reich’s Piano Phase, a 1967 piece designed to be performed by two pianists playing the same piece of music at two slightly different speeds. Here’s classical percussionist David Cossin performing a version of the duet with piano and himself:
This will help you visualize what’s going on: