One of the tracks on 'Kind of Blue' is called 'All Blues'. It's said that not long before the recording took place, Miles Davis gave the players a brief outline of the scales and melodies they would improvise on. The album was recorded with hardly any rehearsal and 'All blues' was recorded on the second take.
'All blues' is related to the blues - a style of early American black music originally performed by one singer accompanied on guitar or banjo. The blues influence can be heard in the 12-bar blues chord structure and the use of blue notes.
Compared with the major scale, some notes, known as blue notes may be flattened by a semitone or 'bent' by a smaller interval.
Blue notes are often found on the third, fifth or seventh degree of the scale. In 'All blues' the seventh note is flattened. Although the key note is G, all the Fs are F naturals (rather than the F sharps found in G major).
The music is in the Mixolydian mode (the white notes on the piano from G to G). 'All blues' is sometimes described as modal jazz.
The 12-bar blues form has three four-bar phrases. The most common chord structure uses three chords - the tonic (chord I), the subdominant (chord IV) and the dominant (chord V).
In the key of G this would be
|G (I)||G (I)||G (I)||G (I)|
|C (IV)||C (IV)||G (I)||G (I)|
|D (V)||C (IV)||G (I)||G (I)|
This pattern can vary in the blues.
In 'All Blues' minor sevenths are added to most of the chords. Some chords are changed more radically. Two G minor seven chords are used at the beginning of the second phrase (using the blue note flattened third). The third phrase uses chromatic chords and more chord changes.
Chromatic harmony uses notes from outside the key to colour the chords. The final chord is an added sixth chord (formed of the triad with an added sixth: G B D E) - a chord which is often found in jazz music of this period.
Here is the chord pattern used in 'All Blues'.
|G7 (I7)||G7 (I7)||G7 (I7)||G7 (I7)|
|Gm7 (I7)||Gm7 (I7)||G7 (I7)||G7 (I7)|
E flat7 (flat VI7)
F (flat VII)
F (flat VII)