In the early 1940s in jazz, bebop emerged, led by Charlie Parker, Dizzy Gillespie, Thelonious Monk and others. It helped to shift jazz from danceable popular music towards a more challenging "musician's music." Differing greatly from swing, early bebop divorced itself from dance music, establishing itself more as an art form but lessening its potential popular and commercial value. Since bebop was meant to be listened to, not danced to, it used faster tempos. Beboppers introduced new forms of chromaticism and dissonance into jazz; the dissonant tritone interval became the "most important interval of bebop" and players engaged in a more abstracted form of chord-based improvisation which used "passing" chords, substitute chords, and altered chords. The style of drumming shifted as well to a more elusive and explosive style, in which the ride cymbal was used to keep time, while the snare and bass drum were used for accents. This appealed to a more specialized audiences than earlier forms of jazz, with sophisticated harmonies, fast tempos and often virtuoso musicianship. Bebop musicians often used 1930s standards, especially those from Broadway musicals, as part of their repertoire.