He retired in 2006, but music has always been his “real life,” Jim Hetland said.

In 1973, Mr. Hetland left the Renaissance Chorus to form his own group, recruiting members with an ad in The Village Voice. In the 40 years since, hundreds of people have lent their voices to the Renaissance Street Singers, in places high and low all over the city — Christopher Street in the West Village, Montague Street in Brooklyn Heights, Central Park, Fort Tryon Park, the steps of St. John the Divine, McCarren Park in Williamsburg, the High Line and the Graybar Passage.

Sigmund Rosen, 77, a group member who met Mr. Hetland in the late ’60s, said his scholarly temperament and organizational know-how helped Renaissance music survive in New York. Since the early ’70s, Mr. Rosen has served as the president of the nonprofit Renaissance Chorus Association, whose stated mandate is to “collect, catalog and circulate the music of the Renaissance period.” Mr. Hetland is the vice president and webmaster.

“We’re a bunch of atheist religious singers,” Mr. Rosen joked.

At performances, Mr. Hetland lays out yellow fliers explaining the group’s purpose. “I’ve always wanted it to be clear that we are singing because the music is beautiful, not because it’s religious,” he said.

The group hasn’t always been greeted warmly. Mr. Hetland said they had been met with bad operatic aria impressions. And once, he said, a woman, dressed in black, began yelling at them: “This is not a church! You can’t sing here! This is not a church! I’m a Jew!” She knocked over Mr. Hetland’s music stand and stormed off. The singers never stopped singing.

“I yelled after her, ‘Half of us are Jewish, too!’ ” he said.

But more often, the Renaissance Street Singers inspire positive emotions. In Grand Central, at least two dozen people stopped in their tracks to listen; they stayed for a minute or a song or 10 songs. A sanitation worker for Metro-North parked his cart in the passageway for 15 minutes to listen. The group has produced two or three marriages, several relationships and many friendships. And people of all ages join, from those past retirement age, like Mr. Rosen, to students like Sherwin Chao, a tenor who is a graduate student at Columbia University.

The harmony among the group’s members says as much about Mr. Hetland as about the music they all share. “John is trusting and transparent and kind,” said Barbara Rosen (no relation to Mr. Rosen), who joined the group after a falling out with her church choir. “He loves people and tries to find the good in everyone.”

Every year, the Renaissance Street Singers perform a public concert in Mr. Hetland’s Chelsea loft. This year, on a Sunday in late February, about 75 people gathered to listen. Mr. Hetland, wearing a blue oxford shirt and tie, greeted each attendee at the building’s entrance, checking names off a list. He moved into the loft in 1976 with his partner, Alan MacKinnon, who for a time sang with the choir. Mr. MacKinnon died in 1997, but the doorbell downstairs still reads Hetland/MacKinnon.

After a brief introduction, the show began. The singers stood in a half-moon formation in front of Mr. Hetland, with a phalanx of chairs spreading across the loft. The crowd watched rapt as the voices rose and fell with a warm, enveloping drone. The group performed Finck’s “Missa In summis,” and then ended with a humorous round written by Mr. Hetland. “Angels, in a human guise,” the chorus sang, “Usually unrecognized.”