As a young man, Mr. Nally dreamed of becoming a classical saxophonist. But by his freshman year of college, he’d switched to voice, and was almost immediately conducting church choirs. In the mid-1990s, he was commissioned by Gian Carlo Menotti’s Spoleto Festival in Italy to form a festival choir, which became his laboratory for the development of a new sound.

“I had come up in this tradition of robust American singing, and that was never really in my ear,” he said. “It doesn’t work in contemporary music, because you can’t hear what the harmonies are. So I started to clean it out, and it started to make sense to me. I tried to find a way to make sounds that could hover, that didn’t have to move forward, that rejected 19th-century ideas about line and linearness.”

It was a sound with the calm purity of early-music performance, but also the agility and flexibility demanded by new music. Above all, it was clear.

And it eventually gave rise to the Crossing, at first a casual reunion of singers who’d loved working with one another, which had its first performance in the fall of 2005. Swiftly deciding to focus on new music, the group barely advertised itself but eagerly threw live recordings online.