NPR’s Tiny Desk Concert with T-Pain and keyboardist Toro. (Susan Hale Thomas)

T-Pain isn’t usually this nervous, so you’ll have to forgive him; he’s preparing to sing about sloshiness and seduction to dozens of lunch-breakers congregated amidst a grid of office cubicles.

It’s a recent Monday afternoon, and the jittery pop singer — famous for his Auto-Tuned R&B hits — has come to National Public Radio’s D.C. headquarters for a Tiny Desk Concert, a stripped-down, single-microphone performance filmed before an audience of NPR employees and posted online soon after.

These Tiny Desk gigs have become a hallmark of NPR Music, a growing branch of NPR whose taste-making powers always seem to be on the rise. Now, after proving itself as a powerful evangelical tool for converting Web-savvy music fans into NPR listeners, NPR Music is aggressively expanding its coverage into hip-hop and R&B.

And it’s working. Just one week after T-Pain’s Tiny Desk visit, the performance had been viewed on YouTube more than­ 5 million times.

“We have a vision that NPR Music can engage with artists all across the musical spectrum,” says Anya Grundmann, NPR Music’s director and executive producer. “We want to be able to tell stories about creative artists across all music.”

There are some particularly interesting stories being told on Microphone Check, an NPR Music blog and interview program co-hosted by NPR’s Frannie Kelley and Ali Shaheed Muhammad of the pioneering hip-hop group A Tribe Called Quest.

In the past six months, the soft-spoken duo have had sprawling chats with superstar rappers (T.I., Andre 3000), legendary producers (Pete Rock, Mannie Fresh) and rising rookies (Y.G., the Underachievers).

“These are really intimate conversations,” Kelley says. “And people want to hear these stories.”

But as illuminating as their interviews can be, not many of them make it to the airwaves. Kelley says they’re working on it; Grundmann says that Microphone Check has the youngest reader demographic of any NPR blog and that it’s being allowed to flower organically.

For Kelley and Muhammad, the goal is to make NPR a central voice in the greater hip-hop conversation. But considering how many listeners still equate NPR with folk music, indie rock, and whatever Bob Dylan happens to be up to, that might seem like a long shot. But maybe it isn’t.

“This was great for me,” T-Pain said after his Tiny Desk performance Oct. 27. “It’s like [NPR is] more in touch. I feel like I’d listen to it now.”

By then, the crowd had dispersed to their work stations to finish their daily tasks. Yusuf Islam — the singer formerly known as Cat Stevens — was due to show up for his Tiny Desk gig in a few hours.

Telling the deeper story

In 2010, Kelley made the most fortuitous typo of her career. In a piece about “The Anthology of Rap,” a bulky tome of classic rap lyrics, she quoted an erroneously transcribed ODB rhyme.

“And then I got this e-mail from somebody who said, ‘I’m Ali Shaheed Muhammad’s girlfriend,” Kelley says. “ ‘I’m sitting next to him and we noticed an error in your post.’ ”

Kelley and Muhammad kept in touch. When she interviewed him about the 2011 documentary “Beats, Rhymes & Life: The Travels of A Tribe Called Quest,” Muhammad asked if and how he could contribute to NPR’s hip-hop coverage.

The duo eventually launched Microphone Check as a Webstream focusing on hip-hop from all regions and eras. “We definitely wanted the entire genre to be represented,” Muhammad says. “Not just mainstream, popular artists, but also the people behind the scenes who had a role in this genre existing.”

Since then, Microphone Check has evolved into an interview show designed to appeal to hip-hop novices and hyper-fluent superfans alike. The conversations are long, and unhurried and thoughtful. The program succeeds because the hosts know how to ask smart questions and they listen carefully to their guests’ responses.

“I’m a very good listener,” Muhammad says. “I think that’s one of the things that makes me a good producer. But it’s a challenge for me because my custom is to listen and absorb what someone is saying and take it in, and not necessarily comment.”

That’s usually where Kelley’s expertise shines — her knowledge is encyclopedic and her quiet enthusiasm is undeniable. Sit her next to a member of one of the most important rap groups of all time and watch the rapper in the interview chair spill his guts.

“As an artist, sometimes you’d rather not do the interview,” Muhammad says. “You might feel the interviewer isn’t educated on you . . . or what you’re about. So [with Microphone Check], there’s an opportunity for a deeper story to be told — a story that’s been missed.”

A really Fresh conversation

Kelley and Muhammad want to keep their formula fluid, so back in May, they invited a couple hundred fans to NPR headquarters for the first edition of Microphone Check Live.

The guest of honor was Mannie Fresh, the veteran New Orleans producer and DJ who helped establish the career of Lil Wayne, the dominance of Cash Money Records and the ubiquity of rap music from the American South.

Fresh is one of those quietly colossal figures in American pop music who — for whatever reason — isn’t often invited to spend an hour discussing his craft in front of an audience. So he talked. About vintage drum machines. About old Mantronix tunes. About his attempts to imitate the vibe of Rush’s “Tom Sawyer.” His excitement and his laughter felt contagious.

And when Fresh was done talking, he jumped from his seat and headed over to a set of turntables for an impromptu and all-over-the-place DJ set that included remixes of Janet Jackson, Kenny Chesney, Trouble Funk and others.

For NPR, this seemed like something entirely new — a public discussion about a form of music that still isn’t discussed enough, and rarely with this kind of depth or care. It also felt like a party.

As Fresh cued up the tracks, fans bounced in their seats. Kelley beamed. But before that, Muhammad offered some purposeful parting words: “Tell your friends to tell a friend to tell a friend — we’re changing things here at NPR.”