Instead of playing a diminished scale over a diminished
chord you can take any chord tone of a diminished chord, lower it a half
step and play a dominant seven with a lowered nine instead. So for an Eb diminished
chord you may substitute it with a D7b9, F7b9, Ab7b9, or a B7b9. The advantage
of this is you will be implying a tonal center and sound more melodic since
diminished scales have no tonal center. Keep in mind that when doing this your
choice of the substitute should be influenced by the chords preceding and
following the diminished chord. For example if you see a Eb diminished chord
followed by say an E minor chord then a logical substitute would be the B7b9
since B7 is the fifth of the following E minor chord.
