A style of music originally based on field shouts and secular songs of the American Negro, featuring repeated sections of twelve measures each in an A-A-B structure. This is a vocal genre, often performed by singing guitarists, with melodic lines characterized by flatted thirds and sevenths. Despite the name, the mood can be happy or sad, the tempo fast or slow. Sometimes called a subgenre of jazz, blues music has its own identity in artists such as Buddy Guy and Ruth Brown. Typical artists in blues-rock, a related style, are Stevie Ray Vaughan and Eric Clapton.