Why is it that blues tunes are notated in a Major key when a blues scale
follows a minor pentatonic pattern?
The basic sound that is used to create the Blues
can be defined as Minor over Major.
The chords in the typical Blues progression follow
the I-IV-V Major Triad pattern of the typical
Tonic-Sub Dominant-Dominant relationship in
Diatonic Harmony. The Blues Scale contains the
7th of all 3 chords, and sets up the sound of
dissonance as a basic melodic device.
The interval that stands out in this relationship is
the Major Seventh Interval, found between the
Third of the I and V chord and one of the notes of
the Blues Scale, and between the Flat Five of the
Blues Scale and the Fifth of the overall key which
is also the Fifth of the I Chord.
This interval, once defined as a dissonance in traditional harmony, is
now a desirable addition to chord voicings in jazz.
By the way, Playing Through The Blues by Griff Hamlin is a decent
resource for learning the blues... a nice start for, and addition to, your
jazz playing.
SPEED
How can I get faster at improvising?
The obvious answer of course - practice!
The more you know your playing tools
the faster you will be able to react and
play what you hear.