Voice instructor Jo Thompson describes Bowie's vocal vibrato technique as "particularly deliberate and distinctive". Schinder and Schwartz call him "a vocalist of extraordinary technical ability, able to pitch his singing to particular effect." Here, too, as in his stagecraft and songwriting, the singer's role playing is evident: historiographer Michael Campbell says that Bowie's lyrics "arrest our ear, without question. But Bowie continually shifts from person to person as he delivers them ... His voice changes dramatically from section to section." In a 2014 analysis of 77 "top" singers' vocal ranges, Bowie was 8th, just behind Christina Aguilera and just ahead of Paul McCartney. In addition to the guitar, Bowie also played a variety of keyboards, including piano, Mellotron, Chamberlin, and synthesizers; harmonica; alto and baritone saxophones; stylophone; viola; cello; koto (in the "Heroes" track "Moss Garden"); thumb piano; drums (on the "Heathen" track "Cactus"), and various percussion instruments.