Theoretically correct scale

Here is an except from Someday My Prince Will Come, bar 9 - 12:

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The Db diminished 7th chord appears as a tonal functioning diminished chord, bIII diminished 7th, that is, analyzed as passing from III-7 to II-7. The non chord tones of the tonal functioning diminish chord are determined by the Key of the Moment, B flat, in this case.

The theoretically correct scale will be as follow:

Note that parenthesized numbers indicate avoid notes.

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A lot of double-flats. As we discussed in the Workbook, we can respell the Db diminished scale to the C# diminished scale for conveniences. After all, theoretical correctness is not required when you are on stage and blowing hard.

Note that parenthesized numbers indicate avoid notes.

What Can You See?

A diminished 7th chord is built with two tri-tones, which means it could represent four dominant chords:

Let's try to fit these chords to the key of B-flat, which is the key of the moment of this song, Someday My Prince Will Come. This is not a theoretical analysis since we are not considering what chord might follow.

• A7 = possible V7 of iii-: the scale would be Altered Mixo
  
• But on stage, we often like to play A7(b9,b13) instead, to make it more interesting
  
• Eb7 = possible SubV of iii-: the scale would be Lydian b7/Mixo #11
  
• C7 = possible V of V: the scale would be Straight Mixo
  
• Gb7 = possible SubV of V: the scale would be Lydian b7/Mixo #11
  

Which one of them has all the chord tones of C#dim7? The answer is A7(b9,b13).

Let's compare the scale:

If you add C natural, which is a #9th of A7, and often added when the b9th is used, the resulting scale is identical. Coming up with a cool phrase on A7(b9,b13) is a lot easier than sight reading C#dim7 and trying to figure out the non chord tones according to the key of the moment.

Another Example

This is an example of non a diatonic functioning diminished chord in another well known standard song, As Time Goes By, starting at its bridge:

Whether the changes are correct or not, you are facing this onstage, sight reading. There is no way the A diminished chord is acting as a diatonic functioning chord, since it is not followed by a half step or the same root. See my workbook.

You must be able to see the chord tone of A dim7. Seeing a chord tone right away is essential to improvisation. Once you see a chord tone, you should see four dominant chords:

The note on the A dim7 chord which does not appear in those four dominant chords becomes tension. Let's examine.

• Gb does not appear in F7 » F7(b9)
  
• B7 is a good match with A dim7 » B7(b9): This has to be the Mixo b9 scale because of the -3rd note of A dim7, which is b9 to B7.
  
• Eb does not appear in D7 » D7 (b9,b13): Tension b13th is added because of the context, that is, proceeded by F-7 and followed by C-7.
  
• Ab7 is also a good match with A dim7 » Ab7(b9): This has to be the Mixo b9 scale because of the root note of A dim7, which is b9 to Ab7.
  

Any one of them will work. You pick one that you like, and blow away.

Just add b9th, but what about b13th?

Let's step back. Here is the summary of the steps, which you need to process in a split second on the stage when sight reading:

1. Identify the chord tones of the diminished 7th chord
2. Produce four dominant chords which share the tritones with the diminished 7th chord
3. Pick one of them you like, hopefully, the one closest to the context, as explained
4. Add b9th then blow

Since we are accustomed to adding the b13th when we blow such phrase, would it work in this situation? It works most of the time, as I did on the D7 to A dim7 example. On the other hand, b13th of Ab7 is F-flat, and it will take away from the context. In any case, improvising live does not need to be theoretically correct, while it is still important to know what you are doing.

End of this subject.