They start with a beat, then add in the bass. After layering the harmony on top of background vocals, the solo shines on top — you wouldn't even know there weren't instruments being played. Named for the pentatonic scales, Pentatonix is a five-person singing group that formed to compete in the NBC a cappella competition show The Sing-Off. Three of its members were friends from high school, but the full group met for the first time just hours before the show to rehearse. Pentatonix ended up winning the competition, as well as the record deal that came with it.

The group members are about to release their new album, PTX Vol. 2, which features original songs. The singers say they hope the record will present their craft in a different light.

"We try to do it in a way where you don't think of it as vocal music; you just think of it as music — as just a song that you're listening to and you don't miss anything," says bass vocalist Avi Kaplan. "We're just a band, and we just happen to use our voices."

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