The stage lights fall, the crowd goes quiet, and four harmonious voices rise up and fill the air. The melodies unfurl into something both familiar and fresh. What comes next may be a classic song by Joni Mitchell or Louis Prima. It may be an old bebop standard or cheeky arrangement of a 1980s hit. But these are arrangements like you’ve never heard them before—containing all the richness of a full band, but performed using just four voices.