text:  The introduction , following a I – IV – I – IV – vi – V – I chord progression , creates a " wall of sound " , as described by Mark Butler , against which the vocals emerge after nearly two minutes . The guitar part played for the remainder of the song features The Edge strumming percussive sixteenth notes . The bass and drums continue in regular eighth and sixteenth notes , respectively , while Bono 's vocal performance , in contrast , varies greatly in its timbre , ( " he sighs ; he moans ; he grunts ; he exhales audibly ; he allows his voice to crack " ) as well as timing by his usage of rubato to slightly offset the notes he sings from the beat . 
  