In modal jazz, improvisers work from musical modes, scales such as the Dorian, held over long stretches, rather than racing through a dense sequence of chords as in bebop. The harmony moves slowly, sometimes resting on a single chord for many bars, which leaves room for melody, space and atmosphere. The theorist and composer George Russell helped push musicians in this direction in the late 1950s.
Miles Davis explored the approach on Milestones (1958) and above all on Kind of Blue (1959), with John Coltrane, Cannonball Adderley and Bill Evans among the players; it is one of the most celebrated jazz albums and was added to the US National Recording Registry in 2002. Its opening track, So What, spends sixteen bars on D Dorian, rises a half step to E-flat Dorian for eight and then returns, a form Coltrane reused for Impressions. The slow, two-chord vamps common in lo-fi owe a good deal to this modal way of thinking.