The Late Beatles Song That Featured Paul McCartney on 'Prepared Piano'
If you were looking for experimental music from The Beatles, you’d probably look to John Lennon first. After all, Lennon was behind the sound collage that was “Revolution 9” and another wild song the band rejected during the White Album (1968) sessions.
But Paul McCartney had gotten out in front of John in this regard. When Paul led the band through the free-form “Carnival of Light” in ’67, he’d long been experimenting with avant-garde music. (According to Ian MacDonald, Paul worked on tape loops and musique concrete as early as ’65.)
By the time The Beatles got near the end of the line, Paul felt ready to bring “prepared piano” to a Fab Four track. In this case, it involved altering strings to get a metallic effect. When George Harrison asked for a different piano sound on “For You Blue,” Paul got to work.
Source: Cheatsheet