D7b9 (Ebb#6#8?)

The very same voicing but very different context.
Second example is just a basic diatonic dom7b9 in Gm:
Am7b5, D7b9, Gm6
The first one is pretty weird for a couple of reasons:
It's in Db so the melody has to be F - Eb - Db so then if the 2nd chord should be a 7b9 it has to be Eb - D - Db in the bass. D is #1 in the key of Db and in this case it should definitely be an Ebb7b9 chord with Gb(4th diatonic scale note) as the 3rd in the tenor part etc but then the b9 is Fbb and the b7 is Dbb and calling this simple melody line "F - Fbb - Db" is just ridiculous.
So for 100% satisfaction the chord notes should be Ebb, Gb, C, Eb and the chord should therefore be called Ebb#6#8...
and that's not that satisfying, right? :)
Maybe we could learn to accept the existence of the #6 even when the same dominant function as the b7?
PS. Thinking the first example in C# instead of Db will not help! ;)

[@harryswanson3383]

There's always this problem with a tritone sub. In Db major as you are here, a V7-I relies on the resolution of Gb and C to F and Db. The leading note rises to the tonic. The tritone sub (Ebb7) has the same movement from the tritone to the sixth (or third, depending how you're voicing it). The leading note C rises to Db in both cases - I would argue that it is incorrect to call that a movement from Dbb to Db, and so the interval between the bass (Ebb) and the leading note (C) is an augmented sixth and not a minor seventh, with both leading to Db.
If you think about augmented sixth chords from the classical and romantic eras, they are essentially tritone subs of II7. Imagine we are in C (a simpler key!) - the German sixth (Ab-C-Eb-F#) is enharmonically equivalent to a dominant seventh built on the flattened submediant (Ab-C-Eb-Gb), but we call the interval an augmented sixth because the notes Ab and F# resolve outwards, both to G. This is one rare situation where I agree with the "classical" rather than the jazz approach - tritone subs aren't really dominant seventh chords, but I can see why they're labelled as such - it's a hell of a lot easier to read a lead sheet that says D7 than Ebb#6 or Ab7(ttsub) or whatever it would be.
So I agree that this has to be Ebb#6#8. I personally dislike the sound of the #8/b9 over a tritone sub, I think possibly because of the voice leading where both notes are going in the same direction to the same note (the root) but with one over a tone and the other over a semitone.
I'm sure you've thought about all of this, but I'm a massive fan and I wanted to add my thoughts. At the end of the day, it doesn't really matter what you call the chord - it's how you use the sounds in your music, and you use really cool sounds in some amazing ways.

[@adamjdorfman]

Ooh, actually thinking about it in C# might help. Because if we think of it as a #15, the melody can be a D# and the bass can be a D with no problem. And I definitely have an easier time with #15 than #6 haha

[@eldloppa2]

Haha aa så ere