During the late 1940s and early 1950s, a jazz style emerged that was related to bebop but was far calmer and more relaxed in character. It was called cool jazz. Performers of cool jazz played in a relatively subdued manner, with a gentle attack and little vibrato. Cool jazz pieces tended to be longer than bebop works and relied more heavily on arrangements. They sometimes used instruments that were new to jazz, including french horn, flute and cello.