 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 <unk> 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 <unk> , ( " he <unk> ; he <unk> ; he <unk> ; he <unk> <unk> ; he allows his voice to crack " ) as well as timing by his usage of <unk> to slightly offset the notes he sings from the beat . 
