D blues scale.
The blues scale is a hexatonic (six-note) scale consisting of the minor pentatonic scale plus a flattened fifth. So to get the A blues scale, for example, take the A minor pentatonic notes and add a flattened fifth (shown here in green):
A C D E E♭ G A
To construct the blues scale from the corresponding diatonic major scale, several steps are needed. Take, for example, the scale of F major, the notes of which are:
F G A B♭ C D E
The relative minor scale of this is D minor:
D E F G A B♭ C
Dropping the second and sixth notes of this we get the notes of the D minor pentatonic scale:
D F G A C
Now adding a flattened fifth gives us the D blues scale:
D F G A♭ A C
The blues in practice
In reality, there's far more to the blues than the plain blues scale. The most obvious performance feature is the flattening of the third and seventh notes (see blue notes). The extent of the flattening varies, from one performer (and performance) and style to another, but essentially involves indeterminate microtones. What's especially interesting about the blues is that although the blues scale has a minor tonality it works over both minor- and major-key chord changes – the latter resulting in a distinctive dissonant yet strangely effective conflict of tonalities.