A great way to alter a dominant harmony in jazz is by using the diminished whole-tone scale. This scale is a combination of a diminished scale and a whole-tone scale. The scale is spelled out: 1/2 whole 1/2 whole whole whole whole (steps). Notice the first half of the scale is diminished and the second half is whole-tone.
There is a much easier way to form this scale. In reality the diminished whole-tone scale is the 7th mode of melodic minor. First let’s take a look at all of our minor scales. We define the minor sound as having a b3. Remember the 6th mode- Aeolian. This is another name for Natural minor. If I compare a Natural minor scale to a Major scale the spelling is: 1 2 b3 4 5 b6 b7 8. (We call it b3 b6 and b7). Natural minor has two different variations. The first variation is called Harmonic minor. Compared to major it is spelled: 1 2 b3 4 5 b6 7 8. (We call it b3 b6) The second variation is called Melodic minor. It is spelled: 1 2 b3 4 5 6 7 8. (We call it b3). It should also be noted that the melodic minor scale is b3 on the way up, and on the way down it changes back to a natural minor (b3 b6 b7). We only care about the way UP. The other minor scale we have is Dorian which is spelled: 1 2 b3 4 5 6 b7 8. (We call this b3 b7).
I mentioned that it is the 7th mode of melodic minor. Let’s look at a C melodic minor scale. C D Eb F G A B C. If we look at the 7th note (B) and go up 1/2 step (to C) we can figure out the key we are playing in. This is the exact same method we used to play modes based on a major scale. A diminished whole-tone scale is really just starting on the 7th note of a melodic minor then going to the 8th note (or 1st note) and continuing to play until I get back to the 7th note. B diminished whole-tone is then played like this: start on B, then go up 1/2 step (to C) and now play C melodic minor!
To sum it up: to form a diminished whole-tone, start on the note (whatever it is you are trying to play diminished whole-tone on) go up a 1/2 step and follow melodic minor. Let’s say I want to play an F# diminished whole-tone scale. I start on F#, go up a 1/2 step to G, and now play G melodic minor. (Remember that melodic minor is really just a major scale with a b3). Here is the F# diminished whole-tone: F# G A Bb C D E F#. The Chord symbol for a Diminished whole-tone scale is G7#9. It might also appear as: G7alt. Another name that it goes by is the Super Locrian. The actual chord contains a b7 #9, b9, #4 and #5. The basic chord compared to major is spelled: 1 3 #5 b7 #9. This is a very tense chord. It offers a lot of tension and a great release when used. As with the other altered dominants, we can substitute this dominant for another if we wish to add tension. The chords D-7 G7 Cmaj, can be changed to D-7 G7#9 Cmaj. This can be done as long as the dominant is resolving up a 4th to the I chord.