Founding work of minimalism, Music with Changing Parts is a piece with free instrumentation. The musicians choose which part to play among the 8 staves of the score. At each indicated cue, the musicians can change part, which produces an abrupt change of instrumentation. While the music is based on a melodic material limited to a few notes that are repeated in patterns that expand or contract, the changes in orchestration refresh the listening experience by producing sonic contrasts. These techniques at work in Music with Changing Parts, written in 1970, will lead Philip Glass to renew his language and move from the monochromatic works that precede it to more dramatic works such as music in 12 parts and especially…