Working in collaboration with “Wilderness Downtown” director Chris Milk and the Creators Project, Arcade Fire caused the most impressive spectacle of Coachella this past weekend. During their final song, “Wake Up,” 2,000 white balls were dropped from above the stage, directly into the crowd. They bobbed around for a minute or two, and then began to change colors, cycling through blue, red, orange and pink throughout the rest of the song and, as it turned out, the encore. Creators Project worked closely with Coachella this year, staging various art events throughout the festival. Other on-stage collaborations came courtesy Animal Collective with Black Dice and Interpol with David Lynch.