Before the singers embarked on the tour, music director Deke Sharon told them: "This isn't the competition, and these guys are not your competitors."

It was a good reminder for the members of some of the country's top a cappella groups - Voiceplay, Street Corner Symphony, and the Exchange - as they began the Sing-Off Live Tour, which comes Sunday to the Keswick Theatre in Glenside.

The three groups had, indeed, competed against one another - on the NBC show The Sing-Off, in which a cappella groups vie to be dubbed the best in the country. (The winner was Vanderbilt University's Melodores.)

Now, they were brothers on the road.

After only a few days of rehearsal, the groups have completed their first week of shows and are beginning to get a handle on working with so many additional voices. The members of each group are used to working with one another, of course, but for the tour, larger ensemble numbers involve all the voices. (Each group does have a 25-minute set unto itself.)

Now they're bringing this supercollaboration to the Philadelphia area.

Alfredo Austin, who spent his childhood in West Philadelphia, sings with the Exchange. He is excited to come back to Philly with his group for the first time. They have traveled to Australia, Europe, and Asia, but this is their first American tour.

Austin - who, according to his mother, has been singing since he was in a car seat - says, "It's really nice for friends and family to see what I've been up to."

If time permits, the 30-year-old tenor plans to show his group mates around town. But only after they put on a great show. Sharon says the audience can expect a show that mixes genres and eras, from Chuck Berry oldies to contemporary hits by Bruno Mars, all a cappella.

He says they'll be tapping into "that traditional street-corner sound."

The music director, called "the father of contemporary a cappella" by Entertainment Weekly, says it's "the oldest music - it remains just as exciting and compelling."

Philadelphia has a long a cappella tradition, with doo-wop and street-corner-harmony groups dating back at least to the early 1950s. The tradition has survived into the R&B era, as heard in the harmonies of Philly's own Boyz II Men. As though in homage to that, Shawn Stockman of that Grammy-winning group serves as a judge on The Sing-Off.

Sharon says too many people spend more time watching others sing than creating music themselves. It's a technological age in which machinery can interfere with raw human emotion. That's what makes a cappella so cool, he says, with its direct, unaccompanied voices. "It's the human element that touches people's hearts."

Sharon was also music director on the film Pitch Perfect. The 2012 comedy centers on an all-female a cappella group trying to make it to a national competition while sticking together as a group. The film was an unexpected hit, grossing more than $113 million globally. He has now wrapped up work on Pitch Perfect 2.

Sharon sees a rising interest in a cappella, but he notes that many people experience the art only through TV or film. There is, he says, "nothing like experiencing it live."

Sharon's motto, "Harmony through harmony," exemplifies how the groups have connected. He says, "It's one big roving party for them."

And, says Austin, the city is invited.

"There's something for everyone, there truly is, for young folks and older folks," he says. "Everyone's extremely talented, and people will walk away wowed."

CONCERT

"Sing-Off" Live

8 p.m. Sunday at the Keswick Theatre, 291 N. Keswick Ave., Glenside.

Tickets: $30-$57.50

Information: 215-572-7650 or www.keswicktheatre.com

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