A lot of the hard work belongs to Ben Bram, who is amazing at making these musical arrangements. Sometimes I feel that he has single-handedly propelled some of the Sing-Off groups into the finals. He was also the music arranger for most of the songs in Pitch Perfect.
And when Ben Brams works with Pentatonix, magic sparks. Together, they've brought us ET, Somebody That I Used To Know, NSync Medley, Evolution of Music and of course, Wizard of Ahhhhs.