The Sing-Off, Sara Bareilles The Sing-Off, Sara Bareilles

Before she sold a million records, before she had a No. 1 song and before she was nominated for three Grammy awards, Sara Bareilles was kind of a nerd, and she's not afraid to admit it.

"We would choreograph dances at parties instead of doing keg stands. We were all so nerdy together," she tells of her college years spent in the UCLA a cappella group Awaken A Cappella.

"My experience in an a cappella group totally shaped me at a really impressionable time in my life as a performer. It gave me a lot of my confidence on stage, because I was someone who was really insecure and felt a little lost in college."

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Fans first got a taste of Bareilles' a cappella chops on the Season 2 finale of The Sing-Off when she performed her hit record, "King of Anything" with The Backbeats, but now her expertise will really be put to the test as she takes a spot on the judges panel this season. The singer-songwriter replaces Nicole Scherzinger and joins the sleeper hit just as it transitions from being a five-episode series timed to the holiday season to a major component of NBC's fall schedule (and the network's answer to Simon Cowell's The X Factor, aka Scherzinger's new employer).

"The decision to join was so easy. I've been a fan of the show since the beginning," she says. "Also, [fellow judges] Ben Folds and Shawn Stockman were a huge draw for me. I'm such a fan and I really respect the way that they handle their judging duties. It made it feel like it was a really good fit for me."

Bareilles' previous experience in Awaken makes her a perfect candidate to judge The Sing-Off. But as someone who was in the shoes of the contestants not so long ago, will she be able to dole out criticism when needed? "It's something that I still am figuring out. I think that I've had access to really amazing producers and music directors who sort of taught me what it feels to give criticism in a way that makes you feel not so defensive," she says. "But I'm doing a disservice if I can't muster up the courage to tell someone that I think they need work."

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But make no mistake: Bareilles is no Simon Cowell-in-training. The Sing-Off was the original kinder, gentler American Idol, months before NBC's The Voice made it cool to be nice. "You have to be able to be objective, and I think we've all learned that over the years by being in this industry — there are moments when you've got to put your game face on a little bit," she says. "What's thrilling about this show is that it is really emotional and human and positive. It's OK to love these groups. We want what's best for them. We want to help them grow."

But with at least four singing competition series on tap for the 2011-2012 TV season (The Sing-Off and The X Factor in the fall; The Voice and American Idol return in January), one might wonder if there is any undiscovered talent left. "I don't worry about that too much. What makes [our show] unique is so embedded in the format of the show, and it's a cappella. No other show is doing that," she says. "Honestly, I don't think the talent pool will ever dry up."

If anything, Bareilles argues that The Sing-Off's success has ensured that the show will have plenty of vocalists to showcase for years to come. "A cappella, in and of itself, is growing exponentially because of the show," she says. "People are inspired to form new groups and we have one group that has been singing together for 30 years. ... Especially as the show is expanding, it's exciting to see the talent pool expand."

The proof for naysayers, Bareilles says, is this season's performances. "I knew the performances were going to be good, but there are a couple of groups that I don't even know how they did what they did," she says. "It's a really intense, emotional roller coaster to be on."

The new season of The Sing-Off premieres on Monday, Sept. 19 at 8/7c on NBC.