Michael Cooper: “It was with some trepidation that I set out last week to try Soundwalk 9:09, a piece the Metropolitan Museum of Art commissioned from … the Pulitzer Prize-winning composer. Composed of sounds recorded in the area, the work is intended for people to listen to on their smartphones as they make the eight-block walk between the museum’s mother ship, on Fifth Avenue, and its new outpost, the Met Breuer, in the old Whitney building on Madison Avenue. What if I did it wrong?”