Bebop grew out of the culmination of trends that had been occurring within swing music since the mid-1930s: less explicit timekeeping by the drummer, with the primary rhythmic pulse moving from the bass drum to the ride cymbal; a changing role for the piano away from rhythmic density towards accents and fills; less ornate horn section arrangements, trending towards riffs and more support for the underlying rhythm; more emphasis on freedom for soloists; and increasing harmonic sophistication in arrangements used by some bands. The path towards rhythmically streamlined, solo-oriented swing was blazed by the territory bands of the southwest with Kansas City as their musical capital; their music was based on blues and other simple chord changes, riff-based in its approach to melodic lines and solo accompaniment, and expressing an approach adding melody and harmony to swing rather than the other way around. Ability to play sustained, high energy, and creative solos was highly valued for this newer style and the basis of intense competition. Swing-era jam sessions and "cutting contests" in Kansas City became legendary. The Kansas City approach to swing was epitomized by the Count Basie Orchestra, which came to national prominence in 1937.