So for those of you who don't know Pentatonix, they are an acapella group that competed on a show called The Sing Off, which was on for 3 or 4 seasons. I believe they were on the third season and won the competition that year. They have since been producing YouTube videos, covering songs from pop culture, and go out on tour. So the novelty here is that it is all acapella, there are no actual instruments used (there are effects - reverb, etc...applied in the recording process, but everything you hear is produced from their voices).