For film festivals, it’s usually easy to pinpoint success — distribution deals drawn up amid the excited buzz of a first screening, new project announcements — but for a music festival like South by Southwest, the tangible effects of an appearance can be much more difficult to gauge.

For starters, there’s the sheer quantity of music on display: SXSW features more than 2,000 bands playing over the course of five days. And while there are plenty of musical success stories that come out of the festival, such successes take on varied forms (a new tour partner, an introduction to a label or, perhaps most importantly, ever-building blog attention) and can often take some time to truly pay off.

Florence and the Machine, for example, first appeared on Stateside radars after playing the fest in 2008, although it wasn’t until this year that her real breakthrough took place, landing gigs at the Grammys and the Oscars. Janelle Monae and B.o.B. were both highly tipped rookies at the fest in 2009, and last month could be seen performing together at the Grammys as well.

Chris Swanson, head of Bloomington, Ind., indie labels Jagjaguwar and Secretly Canadian, says labels rarely sign an act based on a SXSW “discovery” alone, but that doesn’t make the exposure any less important.

“I don’t know that SXSW represents that ‘one moment,’ ” he says, “but it’s often a confirmation of something, or the beginning of a dialogue.”

If nothing else, Swanson — whose labels have 17 acts headed to Austin — mentions that a showcase can be a good litmus test for acts that the label is already interested in. A few years back, he recalls seeing Brooklyn band Here We Go Magic six times over the course of the festival and setting up a deal with the group as a result.

“When you go to watch a band playing with gear that’s not their own, and they have 10 minutes to hook into it, with no soundcheck, setting up in front of an already pretty lit crowd at 2 p.m., people judge the performance by different criteria,” he says. “And what you can do with that stage in less-than-ideal circumstances says a lot about what your band is capable of.”

Christina Rentz, head of publicity for Merge Records — a 22-year-old indie that goes into this year’s fest with blossoming clout, having just notched its first Grammy and first No. 1 record (both courtesy of Arcade Fire’s “The Suburbs”) — agrees that traditional A&R scouting is a difficult proposition at the fest. But she mentions that a showcase can be useful for leveraging the drawing power of a label’s larger bands to get exposure for the smaller ones, as well as introducing new bands on the roster and “branding them to your label.”

“For the smaller bands, it’s important to get in front of all the media at once, because it trends,” she adds. “If all the media are saying the same thing about a particular show, then it makes other writers pay attention. Then you get the write-ups, and the pull quotes, and you can tell people ‘look at this!’ ”

In some cases, the show doesn’t even need to be successful to get the conversation started. Last year saw “witch house” trio Salem all but booed off the Fader Fort stage during its ultra-laconic set. Video of the debacle made the online rounds, the band’s champions offered subsequent defenses of the performance, and by the time Salem’s full-length debut “King Night” rolled around in September, the group had become a flashpoint for debate, and certainly benefitted from the attention.

Of course, having a decent show doesn’t hurt either. Last year, little-known Baltimore duo Wye Oak played the festival shortly after cutting its first release on Merge, attracting hugely enthusiastic notices from the likes of NPR’s Stephen Thompson. A subsequent EP kept the momentum going, and this year the band returns to the fest a better-known commodity with a new full-length work out days before the festival. At no point did SXSW “make” the band, but one can nonetheless chart its ascension through the prism of the fest and see the boost it’s received at each step.

“Everything is about setting up the next thing,” says Rentz. “And fortunately, it’s not the end of the world if it doesn’t happen the way you want. But when it does, it’s awesome.”

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