Don't ask Joe Tarsia to toot his own horn.

Not even when the Sigma Sound Studios owner is hosting a reunion of former employees 50 years to the day since opening the recording studio that is synonymous with the Sound of Philadelphia.

At a South Philly banquet hall on Sunday, the founder of the North 12th Street studio that served as home base to TSOP architects Kenny Gamble, Leon Huff, and Thom Bell and that attracted such out-of-towners as David Bowie and Stevie Wonder made a few brief remarks.

Tarsia thanked the accountant who helped him get a loan to go into business for himself and gave all credit to the Sigma vets gathered before him. "I was able to attract the best technicians, the best engineers," Tarsia said. "And the history speaks for itself. Sigma — not me — has 200 gold and platinum records."

>> READ MORE: David Bowie's Philadelphia

While his guests reminisced over pasta and cannoli and signature sounds from Sigma's 1970s heyday, like the O'Jays' "Love Train" and Bowie's "Young Americans," Tarsia was willing to admit — when pressed — that he deserved some measure of credit.

"If I made a contribution, it was that Philadelphia had a unique sound," Tarsia says. "You could tell a record that came from Philly if you heard it on the radio.

"In those days, before the computer, records had personalities. There was the Motown sound. The Memphis sound. The Muscle Shoals sound. And there was the Sigma sound."

That sound was sophisticated, Tarsia says. "It was black music in a tuxedo." Philly Soul distinguished itself with lush arrangements that sweetened hard-driving R&B grooves with soaring strings. Tarsia gained technical expertise at the Cameo Parkway records studio on South Broad Street starting in 1962, where he worked on records by Chubby Checker and the Dovells, among others. But two years later, Dick Clark packed up American Bandstand and moved to California, and the music industry in Philadelphia collapsed.

In 1964, "the Beatles released 'I Want to Hold Your Hand'," Tarsia says. "Before, everybody was coming to the studio with jackets and ties on, and all of a sudden the musicians were wearing sandals. The culture changed in an instant. It was foreign to me. I was panicked."

Fortunately for Tarsia, Gamble and Huff and Bell were there to fill the void. "The Mighty Three" had been trying to get their foot in the door at Cameo. But, as Bell put it in an interview in 2013, "there weren't too many chocolate folks working in the building" at Cameo's office, which later became the offices of Gamble and Huff's Philadelphia International Records.

>> READ MORE: Thom Bell: No longer Silent in the Gamble and Huff Legacy

Working with Tarsia at Sigma Sound, Philadelphia International immediately had success with songs like Jerry Butler's "Only the Strong Survive," a Gamble and Huff production arranged by Bell and Bobby Martin.

It was one of the first of scores of hits the team would create. "It's the right place at the right time with the right people," said Jay Mark, a recording engineer who was Tarsia's third Sigma employee.

"There were a lot of creative people in Philly at the time," says Mark. "The music was there, and Joe was smart enough to recognize it."

"Kenny brought in these large orchestrations," Tarsia says. "Bell had some classical training. The strings, the horns. Then there's the ambiance, the echo that I used. All that gave Philadelphia a signature sound.  And, of course, if it wasn't for Gamble and Huff and their music, none of it would have meant anything anyway."

Dirk Devlin was Sigma's sixth employee in 1971, starting out as a gofer, "sweeping up, cleaning toilets," during a Bell session for the Stylistic's first album, which produced the fluttery "Betcha By Golly, Wow." Soon, he became a full-fledged engineer.

"It all starts with Joe," Devlin says. "It really does." Devlin, who says Bell had a nickname for everyone he worked with — "I was 'Dirty Dastardly Deadly Dirk'" — worked for Sigma in Philadelphia and in the successful New York studio that Tarsia opened in 1978 in the Ed Sullivan Theatre building now home to Late Night with Stephen Colbert.

When he left the company, Devlin says, Tarsia "cut me a check. I'm not going to tell you how much it was, but it was profit sharing. Joe was incredible. He paid you double time if you worked over 50 hours. And we were working 80 or 90 hours a week. He got the best people because he was good to you. He was the best boss I ever had."

The Sigma sound, Devlin says, is a combination of "the Philadelphia Orchestra and gospel and jazz. And there's nothing subtle about the gospel. If you listen to Teddy Pendergrass, it comes straight from the church. You might as well be at Mt. Zion Baptist."

Devlin has fond memories of Philadelphia DJ Ed Sciaky getting Bruce Springsteen to take a bus to Philadelphia from Asbury Park to huddle with Bowie during the Young Americans sessions in 1974. And he recalls B.B. King and gospel greats the Mighty Clouds of Joy's thrilling visits to North 12th Street. "They all wanted a piece of it," he says.

>> READ MORE: Bruce Springsteen delivers 'Rebel Rebel!' tribute to David Bowie in Pittsburgh

But he points to being the recording engineer on McFadden and Whitehead's 1979 hit "Ain't No Stoppin' Us Now" as his Sigma highlight. "It was great when it was the Phillies' or Sixers' or Eagles' theme songs," he says. "But when Barack Obama walked out on stage to it when he was first nominated to be president in 2008, to have it be presidential walk-on  music, I was awestruck by that."

The success of Sigma's New York outpost, which Tarsia ran from 1977 to 1988, is not as well known. Madonna recorded her first album there, including "Holiday" and "Borderline." The Talking Heads, Whitney Houston, Paul Simon, and Elton John also recorded albums at Sigma NY. The brand's success was built on its Philadelphia track record, says Matthew Weiner, who worked there from 1978 to 1983. "It brought that R&B smarts up to New York."

Tarsia passed Sigma to his son Michael in 1990, and the family sold the business in 2003. In 2015, the building at 212 N. 12th was sold to real estate developers who gutted it before construction stalled. It's now a shell with a historical marker out front that proclaims Sigma "was known worldwide for its distinctive sound and recording innovation."

On Sunday, the former Sigma employees traded memories and told stories of the studio's glory days. Engineer Arthur Stoppe's photographs of staffers and stars were shown in a slide show set up next to the buffet table, where Tarsia and his wife Cecilia cut a 'Sigma's 50th' birthday cake.

Stoppe talked about Tarsia's gift for encouraging competition and cooperation among employees. He remembered recording Robert Hazard's "Escalator of Life" and delighted in telling a Stevie Wonder tale about his 1979 album Journey Through the Secret Life of Plants.

The blind musician was so aware of his surroundings, Stoppe said, that when he handed an engineer a cassette to play, he was able to identify the model number of the tape machine by the sound the door made when it dropped open. "I see you have a Nakamichi 700," he said.

The poignancy of Sunday's soiree was made greater because of the passage of time. "I'm 84 years old now," Tarsia said. "I don't buy green bananas." Cecilia Tarsia added, "It really is like a family. It's astounding how everyone's kept in touch."

Stoppe, who worked for Sigma for almost 25 years, waxed nostalgic about being so busy that a social life was impossible, with staff bonding over Broad Street Diner breakfasts at 4 in the morning after late-night sessions.

"It's pretty overwhelming to see all these people." Stoppe said. "Some came all the way from California. There is a chance that this could be the last gathering."