Twelve bar blues

The twelve-bar blues or blues changes is one of the most prominent chord progressions in popular music. The blues progression has a distinctive form in lyrics, phrase, chord structure, and duration. In its basic form, it is predominantly based on the I, IV, and V chords of a key.

The blues can be played in any key. Mastery of the blues and rhythm changes are "critical elements for building a jazz repertoire".

In the key of C, one basic blues progression (E from above) is as follows. (For the most commonly used patterns see the section "Variations", below.)

Chords may be also represented by a few different notation systems such as sheet music and electronic music. A basic example of the progression would look like this, using T to indicate the tonic, S for the subdominant, and D for the dominant, and representing one chord. In Roman numeral analysis the tonic is called the I, the sub-dominant the IV, and the dominant the V. (These three chords are the basis of thousands of pop songs, which thus often have a blues sound even without using the classical twelve-bar form.)

Using said notations, the chord progression outlined above can be represented as follows.

The first line takes four bars, as do the remaining two lines, for a total of twelve bars. However, the vocal or lead phrases, though they often come in threes, do not coincide with the above three lines or sections. This overlap between the grouping of the accompaniment and the vocal is part of what creates interest in the twelve bar blues.

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