#4 or b5?

[AlteredDave]

It's really cool to see we're at least thinking what the spelling implies. As compared to what someone says etc...

There are many options, depending on what you have to make a decision from and how much your aware of the common practice of the style of the tune.

Fep's reason for spelling was performance related, probably the more common reason for notation, right. You know what you want in a performance situation.... or maybe even more important, you know what you don't want. That can be from a theory or harmonic reason... or just what you hear and who cares why.

M-ster dove into the deep in of the pool, right. He using harmonic context to organize choice of spelling.
Not really any big deal... most people know how to swim'

The 1st example...
His quote;
This one *is* a b5, because, in your context, you're suggesting G7alt (and not G7lyd) as the underlying harmony.

So M-ster is using choice of G7altered as what that G7b5 implies.

I would guess M-ster is using as his reference... common jazz practice... and the spelling also.

Altered Dave I'm assuming your voicing...

X 5 6 5 6 X
3 X 3 4 4 X
X 3 1 3 3 X

Nice lead line of F Eb D. So we know G7altered from Ab mel min is G Ab Bb Cb Db Eb F and the actual chord tones are... G Bb Db and F... wait that spells a G-7b5. ???

Sorry... from jazz common practice we know that there are basically two source for G7 altered, the trial and error or old school method G7 with dim and whole tone usage ... or altered tensions.

The voicings were right,I think in the context of chord quality, functional dominants chords resolving to I or minor i in this case, the common sense to name the chords is to use the altered tones in those chords (either augmented or diminished 5,9's) and that depends in the chord progression from the harmonized scale they are taken from.
Maybe Im wrong..someone wants to correct me?

[JonR]

I can't agree with your first point, since the scale is an altered dominant scale, it needs to have a major third, or else, spelling-wise, it won't spell a dominant scale.

Of course - sorry I wasn't clear. In my point #1, I was simply referring to the 7th mode of melodic minor that some folk (not me) like to link with the altered scale. Strictly speaking, the 7th mode of melodic minor has a diminished 4th. But of course when we use it on a dom7 chord, that note acts as the M3, and the m3 of MM 7th mode becomes the #9.

[JonR]

A good rule of thumb, IMO, is that lydian dominant (7#11, 9#11, 13#11) is used on any dom7-type chord which is not functioning as a V7 (or secondary V7). Most commonly they're bII chords (resolving down a half-step to a minor or major chord) or bVII chords (resolving up a whole step to a major chord). They can also sometimes be IV7 chords.

When V7 chords are altered, they tend to take the altered scale (aka diminished wholetone or superlocrian), or half-whole dim, or - more rarely - wholetone.
A HWdim V7 chord could have a #11 (because there is also a P5 in the scale), but it's not commonlyindicated ("7#11" could in theory accommodate the HW dim scale, but always assume it means lydian dominant).
Occasionally you see altered V7s written as "7#11b13" - which I guess allows for a P5 in the bass .

But the over-riding principle is voice moves between chords either side. The above usages are common because that's how they work best for voice-leading in those contexts.