I first experimented with microtones in XVI (1993), a piece for 16 voices, and in Vera, Chuck & Dave I returned to thinking about the notes between the notes. Charles Ives was inspired by two marching bands playing different tunes in different keys simultaneously, and tried to recreate this effect in his music.
In Vera, Chuck & Dave, I imagine that those two bands are actually playing the same tune in the same key, but the bands are out of tune and out of step with each other. In order to get this effect, a subset of the ensemble –– clarinet, trumpet, trombone, violin and electric guitar –– tunes a quarter tone higher. I later expand on this 'acoustic chorusing' of pitch in Sunshine of Your Love and Decasia.