One significant voice will be absent Friday at the Los Angeles Philharmonic Orchestra's Minimalist Jukebox festival: Jeffrey Dinsmore, 42, a tenor with the Philadelphia choir the Crossing. He died Monday, April 14, of an apparent heart attack at Walt Disney Hall in Los Angeles, just before a rehearsal for the prestigious engagement he had helped arrange.

"Observing Jeff's endlessly practical and pragmatic approach to life, Rebecca Siler, Jeff's partner, who is here with us, has asked us to stay with this project and sing Louis Andriessen's De Materie here on Friday," Crossing artistic director Donald Nally said Tuesday.

Andriessen's music is so intricate that replacing Mr. Dinsmore on short notice isn't possible. Siler, who sings the key soprano part, will go forward with the performance.

Though Mr. Dinsmore had no apparent history of heart trouble, his attack was so severe that paramedics at the hall were unable to save him. "He got the best possible chance," said Nally.

Readily identifiable because of his signature heavily waxed mustache, Mr. Dinsmore was one of the Philadelphia area's most active freelance singers. His past credits included the Opera Company of Philadelphia chorus and St. Mark's Church, and, more recently, St. Paul's Episcopal Church of Chestnut Hill.

Though he majored in voice performance at Westminster Choir College in Princeton, the Moorestown native had a natural talent for marketing, and formed his own Philadelphia company, BeSeenCommunications. As cofounder of the Crossing eight years ago, he became the marketing director (as well as board president) of a group whose modern-music agenda seemed unmarketable.

"If you love what you do and do it really well, people will come to hear it. Jeff sold that, and it worked," said Nally. "None of it was hype because it was all from the heart."

Mr. Dinsmore got hooked on choral singing with the Moorestown High School madrigal group, which he joined at the urging of his father, John, himself often heard in local choirs and musicals. "Jeff loved it, and ended up being student conductor in his senior year," his father said Tuesday.

Mr. Dinsmore's association with Nally began after Westminster, when he was working as a car salesman. Nally was director of choral activities at the Spoleto Festival of Two Worlds in Italy when one of his tenors failed to show up. Somebody suggested Mr. Dinsmore as a replacement. "He said, 'I hate my job, so the answer is yes,' " recalled Nally.

Their collaboration lasted 24 years. Voice aside, Mr. Dinsmore helped bring in important donors, including a recent $10,000 gift from the opera star Eric Owens to commission a new work from Philadelphia composer Kile Smith.

Survivors, in addition to Siler, include his parents, John and Lois; his grandmother, Ruth Dinsmore; and a sister.

Arrangements are being handled by Bradley Funeral Home, Marlton.