While the beboppers were reaching new heights of technical virtuosity in their solos, another group of jazz musicians began focusing more on arrangements and strong melodies. Soloists turned the focus of their improvisations away from speed and harmonic prowess in favor of a less ornamental, more melodic approach. Composer-arrangers such as Gil Evans slowed down the blistering tempos of Bop to a mid-tempo swing, which allowed them to explore subtle harmonies and compositional structures. Cool Jazz's classical influences carried over to its composers' choice of instrumentation; bandleader Claude Thornhill brought flute, French horn, and tuba into a sound that was by turns impressionistic and swinging, progressive and nostalgic. The Cool period represented one of the peaks of jazz's popularity: Dave Brubeck's 1959 album Time Out was one of the first jazz albums to sell more than a million copies.