Pieces can be entirely instrumental or have one or two singers, usually: when there's two lead vocals (that can be men, women or a combination), they sing together on a steady interval.
Pieces can be entirely instrumental. Pieces can have one. This is usually. Pieces can have two singers. This is usually. They sing together on a steady interval. There's two lead vocals (that can be men). There's two lead vocals (that can be women). There's two lead vocals (that can be a combination).