A cappella group Pentatonix, often referred to as PTX, perform at Star94 Jingle Jam that also featured Andy Grammar and NEEDTOBREATH at the Fox Theatre on Monday. Pentatonix formed in 2011 and came to prominence the same year by winning the third season of The Sing-Off on NBC, earning them $200,000 and a recording contract with Sony Music. (Akili-Casundria Ramsess/Special to the AJC)