There isn’t a musical instrument in sight in Wardell Quezergue’s living room. The city’s most in-demand arranger works on a card table filled with a dozen pencils, a pencil sharpener and lots of sheet music.

“I really don’t play the piano,” Quezergue says of his work habits. “I can get on it and play chords. If I can hum something, I can play the chords but not the melodic lines or the fills. When somebody wants me to arrange a song, all I have to know is what key it’s in, and I work from ...