Since winning The Sing-Off in 2011, the group has developed an impressive career in the years since, including three Grammy. Mitchell Coby Michael Grassi (born July 24, 1992) is an American singer from Arlington, Texas. Known for his high tenor voice, [1] [2] Grassi came to international attention as a founding performer in two groups—the a cappella quintet Pentatonix, and the duo Superfruit with Pentatonix bandmate Scott Hoying.