Jazz blues

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Jazz blues is a musical style that combines jazz and blues.

The term also refers to any tune that follows the standard 12-bar blues chord progression, whilst being played in the jazz style, rather than the traditional blues style. Blues music was a major influence in the development of jazz, and such tunes -- "jazz blueses" -- are extremely common in the jazz repertiore. (In addition to the chord progression, jazz players borrowed many other stylistic devices from the blues, such as blue notes, blues-like phrasing of melodies, and blues riffs.) A jazz blues will usually feature a more sophisticated -- or at any rate a different -- treatment of the harmony than a traditional, "blues" blues would, but the underlying features of the standard 12-bar progression remain discernable. One of the main ways the jazz musician accomplishes this is through the use of chord substitutions: a chord in the original progression is replaced by one or more chords which have the same general "sense", or function, but which add a different color, or add some secondary, shorter-term, harmonic movement within the span of the existing overall harmonic movement. An important example of this occurs in the 9th and 10th bars, where the usual blues progression, V --> IV, is almost always replaced by the typical jazz cycle-of-fifths progression ii minor --> V. The 12-bar blues form, in Bb, often becomes

Bb7 / Eb7 / Bb7 / Bb7
Eb7 / Edim7 / Bb7 / Dm7-G7
Cm7 / F7 / Dm7-G7 / Cm7-F7

Where each slash represents a new measure, in the jazz blues. The significant changes include the Edim7, which creates movement, and the iii-VI-ii-V turnaround, a jazz stapler.