In 1971, Sigma Sound Studios was the epicenter of Philly soul.

The Stylistics recorded their self-titled debut there. Laura Nyro and LaBelle cut the collaborative album Gonna Take a Miracle. Todd Rundgren performed a live radio broadcast.

And that year another group, not as well-known, also made music at Sigma that has stood the test of time.

The West Philly teenage group The Ultimates recorded a sweet, heartfelt song called “Why I Love You” that got little attention when it was released.

But now, the song has been rediscovered as a lost soul music classic. And it’s giving the trio of Monica Thornton, Debra Herbin, and Shirley Carter — now in their 60s — a new audience, half a century later.

“It is awesome, and surprising,” says Herbin. “It’s been a good ride, and it continues to be a good ride.”

The surprises have been many. An original “Why I Love You” 45 rpm vinyl record, which features the protest song “Gotta Get Out” on the flip side, has sold for as much as $4,000 on eBay.

Max Ochester, who owns the Brewerytown Beats record store in Philadelphia has reissued the single on the BB label.

He originally bought a copy of the record for $5 from a local collector in 2018 without ever having heard the song, which was written by Philly tunesmith and Smokey Robinson acolyte Kenny Fuller.

Soon thereafter, Ochester learned why “Why I Love You” is so coveted. It was originally issued on Valentine Records — named after Thornton’s aunt, Evetta Valentine — in a batch of no more than 500 records. Fewer than 25 still exist.

But the recent demand for “Why I Love You” springs from a surprising source that demonstrates the ability of an innocent love song to transcend time and place.

Over the last decade, “Why I Love You” has a become a fixture on lowrider music playlists that prize rare, vintage soul and R&B, a soundtrack to “low-and-slow” Chicano custom-car culture in Southern California.

The song has garnered over a half million hits on various lowrider playlists on YouTube. “Oh my God,” says DJ Anthony Santana, host of the Santana Soul internet radio show, talking by phone from Los Angeles. He rhapsodizes over “Why I Love You,” which he first heard 10 years ago.

“Just the harmonies. And the lyrics, that will cut your heart. A lot of women love that song. You play that song out here, and all the women will get up off their feet and dance.”

Santana plans to bring The Ultimates out west this summer, for a yet-to-be-named lowrider music and car festival in an outdoor setting on July 30.

Along with their bandleader, Mitchell Hunter, The Ultimates have been playing gigs regularly in recent years, particularly in the Media area in Delaware County, where Hunter lives.

In November, Thornton and Herbin sang at a daytime food truck festival at Linvilla Orchards, each wearing a black cap emblazoned with the word “QUEEN.”

And along with the July trip to California, there are other high-profile gigs in the offing. A Feb. 12 show at City Winery Philadelphia in which they were to open for and be backed by York Street Hustle has been postponed. But on Feb. 12, the band will join Low Cut Connie’s Adam Weiner on the band’s Tough Cookies livestream.

“I’m super thrilled,” Weiner said. “These ladies are beautiful and fantastic, and I can’t wait till people can see them do their thing. ‘Why I Love You’ is such an amazing piece of soul music. It’s mysterious and nebulous and familiar at the same time.”

The Ultimates half-century sojourn began when Thornton, Herbin (then Debra Gunn), and Carter (then Shirley Graves) were best friends and classmates at Shoemaker Junior High in West Philly.

They started performing at block parties when they were 10, at first lip-syncing to Supremes songs like “Stop! In The Name of Love,” showing off dance moves they had practiced in front of a mirror.

Then Evetta Valentine had a revelation.

“Somehow, my aunt realized that we could actually sing,” says Thornton, sitting on a couch on a Sunday afternoon in her home in the Carroll Park neighborhood of West Philly.

Her fellow Ultimates were on either side of her in the rowhouse that formerly belonged to Valentine and served as their rehearsal space on the same block they grew up on. In a display case, there’s a picture of Thornton’s aunt and her husband, Melvin, who served as driver and MC. “We called him the Amazing Melvin!” Carter recalls with a laugh.

“She put us together and had us do luncheons and teas, and some church stuff,” Thornton says of Valentine. “She had the insight to see something in us that we didn’t see in ourselves.”

Valentine also had the ambition to go searching for original songs for the girls to sing. Fuller was 18, and five years older than the Ultimates when Aunt Evetta brought him to the house.

“When he saw we were kids, he was like ‘Oh no, no!’ ” remembers Carter. “But when we opened our mouths and started to sing, he changed his mind.”

In the two hours the Ultimates spent at Sigma — all that Aunt Evetta could afford, they assume — they worked on getting the languorous groove of “Why I Love You” down.

“If love could only be spoken, without hearts being broken,” Thornton sings dreamily, before her bandmates’ harmonies come in. Then in 20 minutes, they knocked out “Gotta Get Out,” which pushes against claustrophobia in a more rugged arrangement. “I just gotta see,” Thornton sings, “What the world’s trying to do to me.”

The Ultimates had plans to make it big. “We were going to win Grammys, we were going to be stars,” Thornton says. The single got limited radio play and earned them audiences with Philly radio legends Georgie Woods and Joe “Butterball” Tamburro, as wells as an audition with Kenny Gamble at Philadelphia International Records’ Broad Street office. No big break came from that, or Fuller’s passing “Why I Love You” to Smokey Robinson in hopes of getting it to Motown’s Berry Gordy.

The Ultimates won talent competitions at the Showtime at the Apollo in New York and another one at what is now Cheyney University. “The trophy was bigger than we were!” Herbin says.

But the big time never arrived, though Evetta Valentine booked the group from Florida to Nova Scotia, and even sent the girls to charm school to prepare for stardom. “How she did it, I don’t know,” Thornton says, marveling at the tenacity of her aunt, who worked for Blue Cross & Blue Shield.

The three women and Hunter have stories to tell about trips to the South that turned into weekslong residencies in Sheffield, Ala., and Roanoke, Va., sometimes due to car trouble that left them stuck there. And one memorable visit to Muhammad Ali’s house in Cherry Hill, with Valentine somehow gaining a private audience, singing for the champ. “He had shag carpet on the walls,” Herbin says.

The trio split amicably toward the end of the 1970s. Herbin worked in food services and the tax revenue department for the City of Philadelphia, a job from which she recently retired. Carter has been a librarian for Philadelphia public schools.

Thornton worked “lots of odd jobs,” while singing in alternate versions of the Ultimates and other groups. All three women raised families and are now grandmothers. And while Herbin and Carter didn’t sing professionally, they made music part of their lives. “I sang wherever I was,” Herbin says. “The joy of music. It’s a stress reliever.”

Hunter had lost touch with the group but tracked down the three women, who all still live in the neighborhood they grew up in, about a decade ago. They began performing in Delaware County venues like the Dog House Saloon and Pinocchio’s, mixing in Marvin Gaye and A Taste of Honey covers.

» READ MORE: ‘Philadelphia is the city that sleeps on itself’: How a Brewerytown record store owner is shining a light on our overlooked musical past

They knew that “Why I Love You” was up on YouTube, but had no idea of the extent of their new following until connecting with Ochester, who has become an important musical archaeologist of underappreciated Philadelphia jazz and soul music.

“We have a another chance to do what we love to do,” Thornton says. “That’s the best part about it for me, and I’m sure that it’s the same for Debra, and Shirley and Mitch. Because singing is so much a part of me. God works in mysterious ways.”