In March, Sigma Sound Studios was approved by the Pennsylvania Historical and Museum Commission for a historical marker. The North 12th Street studio is one of the birthplaces of The Sound of Philadelphia, and it's where pop classics such as David Bowie's "Young Americans" and Elton John's "Philadelphia Freedom" were recorded.

That building recently was bought for $1.55 million for, of course, new apartments and condos. Famed recording engineer Joe Tarsia opened Sigma in 1968 and sold it in 2003 (to contractor Mario Santoro). Sigma artists such as Gamble and Huff, and Thom Bell - put their tapes in the good hands of Iron Mountain Entertainment Services in Royersford. But Tarsia donated his collection of music, studio gear, and Sigma ephemera to Drexel University for storage and preservation.

Tarsia's tapes - many unmastered, unmixed, and unproduced - did not lie there unused. Toby Seay, an associate professor in Drexel's music industry program, is collaborating with Reservoir, an independent publisher with rights to the long-gone Philly Groove Records label, to create newly produced versions of 16 of Sigma's unproduced tracks.

Eight of Seay's students are turning long-unheard, pre-disco cuts from Sigma artists into fresh, raw R&B tunes with clean, vintage vibes. If everything goes as planned, Drexel's Mad Dragon label and Reservoir plan to release a jointly produced album.

At the University Crossing building at Drexel, students in Seay's class, Uncovering the Philly Groove, work with raw vocal and instrumental tracks. There are rooms filled with "Sigma stuff," Seay notes, sifting through boxes of Tarsia's gold records - the single "Shame," by Evelyn "Champagne" King, and the album To Be True, by Harold Melvin and the Blue Notes ("featuring Theodore Pendergrass," reads the award). Deep in the building is a temperature-controlled room where industrial shelves are stacked with cases of reel-to-reel tapes.

"These are the remnants of what was left over after Tarsia sold Sigma," says Seay, who took over the preservation of that Sigma/Drexel catalog in 2007. "This was all in storage."

Seay says the Sigma tapes came in two tranches; 6,200 pieces between 2003 and 2005, then 500 pieces after the building's most recent sale. "The Realtor called and said, 'Hey, the basement is full of tapes,' so we grabbed them, and those are right here," Seay says, pointing to boxes of tapes whose contents have been noted but whose sounds have yet to be digitized.

"We don't own the rights to what's on them," Seay says. "We own the tapes. We can't do anything with them unless we get permission." So Seay enlisted fellow music business professors and students to contact publishers and license-holders. Bobby Eli, guitarist with Gamble and Huff's house band, MFSB, and a producer of countless Sigma/Philly Groove sessions, "has been valuable," Seay says, "as he knows where the bodies are buried."

"Philly's music circles are small," says Faith Newman, who runs Reservoir Media. "We find each other." Newman tracked down Stan Watson, owner of Philly Groove - a label he started in 1967 with songwriter/arranger Thom Bell - in Jupiter, Fla., to buy his catalog. "Once we acquired it, the next search was for actual assets - the tapes." Newman found boxes of mastered and unmastered reels in Florida, while Eli, a Reservoir friend throughout the years, led her to additional quarter-inch tapes of outtakes, bare vocals, instrumental sessions, and multitracking sessions - all in Drexel's possession.

Seay and Newman brainstormed. "What if these tracks got finished?" she asks. They decided to involve Seay's students in producing unfinished songs - in accordance with how their contemporary sensibilities hear things in 2015. Seay says: "And they were free to do as they pleased."

Seay's sophomore producers listened to the tracks, selected the ones they wanted to work on, and then produced them. But, tellingly, they decided not to employ the tricks and gadgets of the moment. No samples, no Auto-Tune. Instead, they elected to produce their chosen tracks - Sound Experience's "It's a Funky Thing," with its bright brass, tribal rhythm, and fuzzy guitars; several heartbreaking Ben Aiken ballads - with warm, vintage tones and dry vocal effects, much as producers would have done in 1968 or 1971. They listened not only to the musicians, but also to the era's producers and how they wanted things to sound.

Liz Rosenberg, 20, made rough vocalist Ernest Wright's "I'll Move the World for You" into a red-hot ensemble piece in which the instruments bleed into one another, for a live-in-the-studio sound, rather than something cold and isolated. "They recorded in one room," Rosenberg says, "and that's how I left the sound."

Brendan Monahan, 20, agrees with her approach. He made his Terry Collins tune, "Actions Speak Louder Than Words," into something clean - "these tracks were pristine to start with," he says - yet thick with the presence of all the other instruments.

"That's how they - and we - maintained the feeling in the mix," Monahan says. "That's why these songs, old or new, groove."

The album project is hoped for at the end of this year - including some tracks remixed by Philly-born master DJ/producer King Britt.