You know you’re at an NPR-sponsored gig at South by Southwest — the annual music festival — because everyone is carrying a tote bag.

Organizers hand them out at a nightclub on Sixth Street during NPR’s Thursday afternoon SXSW concert, for which the line is stretched down the block. Inside the canvas sacks: a T-shirt, a CD, a beer koozie.

But the fans didn’t come for the swag. They came to see their favorite new bands — bands that swarm SXSW every year with big dreams. One day, with any luck, these groups will be smiling for magazine covers, singing on late-night television shows and . . . hearing their music streaming on NPR’s Web site?

Forget the totes — NPR has a brand new bag. The Washington-based news outlet has emerged as an influential powerhouse in a splintering music industry thanks to the growing popularity of NPR Music, a Web site that has connected with music fans by premiering new albums, streaming live concerts and landing exclusive interviews.

How big of a deal is NPR in the music world? Bertis Downs, manager of R.E.M., says NPR’s endorsement now carries as much cultural weight as an appearance on “Saturday Night Live” or the cover of Rolling Stone. “When we sit around thinking, ‘How do we get attention?’ — they’re at the top of the list,” says Downs, who recently helped R.E.M. get its new album streamed on NPR Music. “We know that’s where the audience is.”

The audience is growing. In 2011, NPR Music has averaged about 2.1 million unique visitors a month, putting the site somewhere between, which pulled in 7.1 million unique visitors in January, and, which drew just shy of a million that month, according to Nielsen.

Traffic on NPR Music has quadrupled since the site launched in 2007, and it currently accounts for about 14 percent of the eyeballs visiting And those figures don’t even include the millions of radio listeners who catch the audio features that NPR Music pushes to NPR’s various news programs.

But as the audience for NPR Music grows, it appears to consist of a demographic that’s actually shrinking: music fans who still buy music.

When NPR pushes a group, “there’s a spike in sales and chatter online,” says Steve Martin, the publicist for Radiohead, Arcade Fire and Paul McCartney — all of whom have felt a tangible boost from NPR’s support. “It’s something that reaches an audience that a lot of other people don’t reach.”

And the fact that NPR has music fans reaching back into their wallets has forced both independent and major labels to make NPR Music coverage a top priority in their publicity campaigns.

Label representatives for British soul singer Adele say that NPR was an “important piece” of the publicity strategy that pushed her new album, “21,” to the top of Billboard for two weeks earlier this month. NPR Music recently streamed both the album and an exclusive live performance.

For lesser-known indie acts, NPR Music’s stamp of approval can feel downright momentous.

Take Tune-Yards, the avant-pop troupe from Oakland, Calif., that performed NPR’s Thursday afternoon gig at SXSW. Between songs, bandleader Merrill Garbus sang NPR’s praises from the stage: “I didn’t occur to me how much independent artists depend on NPR.” Then she asked the audience to raise their right hands and “pledge to do everything possible” to support National Public Radio.

It was a different kind of pledge drive. And everyone already had a tote bag.

Back in Washington, a week before SXSW, 18 NPR Music staffers and interns huddle in a fifth-floor conference room. It’s been a good 2011 for NPR Music. They’ve just launched an exclusive series of interviews with Jack White. They recently hired Los Angeles Times pop music critic Ann Powers, one of the most respected music scribes in the game. And to coincide with the start of SXSW, they unveiled a redesigned Web site.

Spirits are high, but when it’s announced that rapper Bun B won’t be able to perform at one of the three concerts NPR is broadcasting from Austin, the room lets out a deflated groan.

That’s because despite its growing influence, NPR Music is still battling a stereotype. Some say its focus is too indie-centric. Too folky. Too white. And it’s a reputation NPR had long before the launch of the site.

“The [on-air] news shows had a lot of hard times doing hip-hop and rap,” says Bob Boilen, 57, host and creator of “All Songs Considered” and veteran staffer at NPR Music. “Every time we’d do a piece, we’d just get bombarded with letters like, ‘Why are you playing that crap?’ ”

Boilen’s career at NPR took shape when he was bombarded with much nicer letters, praising the songs he played between segments during NPR’s flagship news program, “All Things Considered,” which he started directing in 1988.

“It made me very painfully aware about how radio was really failing a lot of people,” Boilen says. “There’s a lot of music being put out that nobody was playing.”

So in 2000, he launched “All Songs Considered,” an online multimedia program he still co-hosts with fellow producer Robin Hilton. In 2007, “All Songs Considered” would become the backbone of NPR Music, an online hub that would premiere new albums from the likes of Bob Dylan and McCartney, stream concerts from the nearby 9:30 Club and Black Cat, host a handful of lively blogs and share the best music content from NPR’s 13 partner stations across the country.

But as they overcame one stereotype — “People used to think: singer-songwriters,” says Boilen — NPR Music stepped into another, becoming largely associated with the indie rock acts that still gobble up most of the site’s bandwidth.

To counter that perception, NPR Music has started to push in new directions by embracing R&B artists (Raphael Saadiq), dancehall reggae singers (Gyptian), even exteme metal acts (Aggaloch).

“They’re huge supporters and you can see the impact right away,” says Saadiiq, who performed at a Wednesday night SXSW concert that NPR Music broadcasted. “I’ve been able to play to a much larger crowd. . . . It helps me branch out.”

With a multi-generational staff, diversifying the programming has become a team effort. “It’s not just like Bob learns what the kids are doing today and the kids learn what the Velvet Underground was really like,” says Patrick Jarenwattananon, 25, the staffer behind NPR Music’s jazz blog, A Blog Supreme. “Everybody has a niche or two. . . . You can help correct each other’s blind spots.”

Like many of his colleagues, Jarenwattananon’s desk is cluttered with CDs, making the NPR Music offices on Massachusetts Avenue NW look more like a college radio station than a newsroom.

Fans already know what it looks like, thanks to Boilen’s Tiny Desk Concerts, for which NPR films an artist performing a song or three next to Boilen’s desk. (The title is a riff on Boilen’s post-punk band Tiny Desk Unit, which played the inaugural show at the 9:30 Club on F Street NW back in 1980.)

More than 100 artists have performed next to Boilen’s desk since 2008, including a few pretty big names: Tom Jones, Mavis Staples, Los Lobos. But of all the Tiny Desk Concerts, French rock band Phoenix drew the biggest digital crowd, having received almost a million views.

Also popular are NPR Music’s exclusive album streams, dubbed First Listen. They started in 2008 when Sony came knocking, hoping to stream a new Dylan album, “Tell Tale Signs.” “We were flabbergasted,” Boilen says of Dylan landing in his lap. “Then the floodgates started opening.” Now, NPR Music streams new albums from a handful of artists every week, helping the site stay true to its mission of discovery.

Discovery seems to be the subtext of Thursday’s gig. The bill mixes up hot indie bands (Wild Flag, the Antlers) with less familiar names (bass saxophonist Colin Stetson, Malian singer Khaira Arby). The young crowd sips PBRs and soaks it all in. (In addition to helping musicians, NPR Music is helping bring a new generation of listeners into the fold.)

The show is off to a smooth start — the second of three concerts that NPR Music will be streaming online during SXSW. They’re also boasting recorded footage of a surprise performance Jack White gave in a parking lot on Wednesday afternoon — a stunt Boilen was hipped to after recently interviewing the former White Stripes frontman.

But while the music played, the House of Representatives was busy back in Washington voting to cut funding for NPR. That news comes only a week after a secretly recorded video of an NPR fundraiser disparaging conservatives forced NPR chief executive Vivian Schiller to resign last week.

But at SXSW, 1,522 miles away from the nation’s capital, budget cuts and video scandals feel very far away — especially when Stetson has awed the early afternoon crowd. He uses cyclical breathing to coax big, beautiful, uninterrupted ribbons of sound from his saxophone. Based on the crowd’s wide eyes, many are seeing him for the first time.

Few eyes are wider than Boilen’s. “What planet did that come from?” he wonders, pushing his way through the crowd after the music stops.

Tough to say. But fans know they heard it on NPR.