 " Piece of Me " is described as being backed by a " electro instrumental track " and performed in an insistent pop groove . The song is composed in the key of C ♯ minor with a time signature in common time . The melody runs through a down @-@ tempo dance beat . Spears ' vocals span over two octaves from D ♯ 3 to D ♯ 5 . They are heavily synthesized and are constantly pitch @-@ shifted . The track consists of over @-@ the @-@ top vocal distortions , causing a split sound effect , making it difficult to discern which voice is Spears ' . Background vocals were also provided by Swedish pop singer Robyn . Christian Karlsson and Pontus Winnberg sing the line " Extra ! Extra ! " during the chorus and writer Klas Åhlund sings the repeated " piece of me " line in a <unk> voice . Dave De Sylvia of Sputnikmusic drew comparisons to the songs in Robyn 's Robyn ( 2005 ) , specifically to her single " Handle Me " . 
