“The World Unseen,” on her album “Black Cadillac,” “gained some curves and some sweetness that I didn’t realize was there,” she said. “We recorded that really late at night, a live track, and it wasn’t that good of a vocal. The producer said he wanted to get a better vocal so we did it a few more times, but we kept going back to that live version. I keep it in a certain part of my voice. If I do it too breathy it sounds cloying. If I hit it too hard, it sounds like rock.”

But thinking things through goes only so far. For one melody, Mr. Simon started out using the words “going home,” he said. “But I said I’m not going to write ‘going home.’ Nothing interesting about that,” he said. “Then I stumbled on this word, ‘Kodachrome,’ which of course, had no meaning.”

In Dr. Levitin’s lab, Mr. McFerrin gamely tried several experiments, including seeing how long he could hold his hand in ice water while listening to different types of music (an effort to find out if music can ameliorate pain). He described a story by Hermann Hesse in which a violinist, granted his wish to be the best musician he can be, vanishes as soon as he starts to play.

“He completely disappears into the music,” Mr. McFerrin says on the video. “And I think that’s actually a big key to a successful creative moment for me, is when I disappear, and maybe the audience disappears into the music and becomes so engaged in the music that you forget that you’re even there.”

As Ms. Cash put it: “Some things you can break down, and some things are ineffable. Some things are just part of that mystery where all creative energy comes from. It’s part of the soul. Music is an ever-moving blob of mercury.”