NEW YORK — It's a plain little room. The size of a small garage, maybe.

For Detroit, this is a very important 150 square feet. Here, on the fifth floor of an office building 500 miles from the Motor City, are the most valuable raw materials in the city's cultural history.

This is Universal Music's Motown vault, and these are Motown's original session tapes: the reels that rolled in the studio, capturing what would become some of the most beloved sounds in popular music.

This vault is a way station for the tapes as Universal staffers do their work, creating digital archives, performing restoration work and extracting songs for an array of Motown projects. When the reels aren't here, they're in heavily guarded, climate-controlled facilities in Pennsylvania and New Jersey with Motown's full archive of 30,000 reels.

Half a century after Motown's inception, the music's staying power is unquestioned. America and the world are still grooving to Motown. Songs by Stevie Wonder, Marvin Gaye, the Temptations, the Supremes, Smokey Robinson and the Four Tops continue to rack up radio play that rivals today's young hit-makers.

Founder Berry Gordy Jr. says Motown's 50th anniversary is “really about celebrating the unsung heroes as well as the ones everybody knows.” Years ago, those unsung heroes were fearless salesmen, patient artist trainers and other offstage personnel. Today, they're the core team of six people in this office, along with staffers across the country, doing the work that keeps Motown's music thriving.

“Universal is the caretaker of the legacy, and we take that role very seriously,” says Harry Weinger, vice president of Universal's catalog division. “Motown is still alive. It's not some creaky museum piece. It's real.”

Motown Records, sold by Gordy 20 years ago, remains an active label - people elsewhere in this building work with contemporary acts. But nostalgia has been big business for the company since the 1980s, when oldies radio took off and Hollywood began to tap the catalog.

“I always knew it would become valuable,” Gordy says. “We were locked into the baby boomers early, and they followed us right down to where we are now. And now their kids, their grandkids, are getting a taste of something they loved so much.”

Lamont Dozier and brothers Brian and Eddie Holland cooked up many of Motown's biggest smashes, including hits for the Supremes, the Four Tops and the Temptations. Recently, for the first time since the '70s, they began writing together, composing songs for an upcoming Broadway production of “The First Wives Club.”

All are in their late 60s, still radiating the sort of easy cool that comes from knowing you've been really, really good at something.

Watching them at the studio board dissecting the Four Tops' “Bernadette” is a music nut's fantasy. Glimmers of recognition sweep across their faces as the song unfolds. They still hear this stuff in a way nobody else ever will, the sonic elements processed in their brains the way a painter discerns his own strokes.

Brian Holland's fingers begin to toy at the faders. Midway through the song's second chorus, the instruments are muted, and all pause in awe as Levi Stubbs' vocal roars alone through the room, droplets of fire dripping from his voice.

Another song is up: the Supremes' “You Keep Me Hangin' On.” The multitrack starts rolling, and the decades again vanish. A young girl - Flo? Mary? - clears her throat at the microphone. Brian Holland's count-in rings out: “One, two, one-two-three-FOUR!”

As the Funk Brothers swing into the flashy groove, the Hollands and Dozier recap the standard H-D-H process: Lamont and Brian conceived the music at a piano, often with unorthodox chording that puzzled Motown's band (and still prompts strangers to pester the trio for answers).

Eddie then crafted lyrics, seeking to capture “whatever that melody and track was saying.” Lamont and Brian worked with Motown's band to flesh out arrangements, keying in on drummer Benny Benjamin and bassist James Jamerson and building from there.

“Did we know exactly what we were doing? I can't say,” says Eddie. “But we knew exactly what we wanted.”

“You Keep Me Hangin' On” was a relatively complex production. Diana Ross vocals are double-tracked to create a crisp sizzle. A piano and organ are tucked subtly into the mix. The song's signature dee-dee-dee lick mimics a teletype machine.

“We didn't have synthesizers then,” says Dozier. “So we had to be really on our toes in coming up with innovative stuff. Fun stuff.”

The track finishes with an unfamiliar flourish: Ross croons a closing coda, and a strum of 12-string guitar brings it to a wrap.

Brian Holland lights up in recognition at the original finale. “I kind of liked that better,” he says. “But you had Berry going, ‘Nah, you gotta fade the thing out.'”