Over the years, jazz has changed and developed, but it has retained or kept its basic quality. One of the forms of music that contributed to the development of jazz was the blues. About a third of jazz music is in the blues form. So are over half of the popular rock and roll pieces. Even some of the country and western music of the United States is in the blues form. A major step in the development of jazz was taken by musicians in New Orleans. New Orleans jazz, sometimes called dixieland, had the deep emotion of the blues and the Black spiritual as well as elements of ragtime and European folk music. According to the passage, what is one characteristic of dixieland music?