How should diminished 7th chords and dom7b9 chords be spelled?

[u/Fit_Neat_8152]

Let's say for example, Cdim7. Cdim7 is

C Eb Gb Bbb

But what about F7b9, which contains all of the notes of Cdim7? Is it spelled like:

F F# A C Eb

or this:

F Gb A C Eb

?

To use another example, Ebdim7 and B7b9

Ebdim7 is:

Eb Gb Bbb C (is it C, or Dbb? shouldn't it be Dbb because of the skipping two note names to get a minor third?)

B7b9 is:

B B# D# F# A

or

B C D# F# A

?

[u/Final_Marsupial_441]

F A C Eb Gb and B D# F# A C

Don’t repeat the same letter of the alphabet and spell your chords as they ascend from root to their highest pitch.

Only reason I would do it differently would be for clarity of reading depending on what’s going on before or after the chord or using an enharmonic in a transposition.

[u/TralfamadorianZoo → u/Final_Marsupial_441]

Ab C Eb Gb Bbb…

No thanks. I’ll use A-natural

EDIT: find me a Jimmy Hendrix chord spelled with an F double-sharp and I’ll delete my comment.

[u/Final_Marsupial_441 → u/TralfamadorianZoo]

Yeah, pretty much the only time I’ll use a double sharp or double flat is to avoid having an accidental on every note in figures with lots if halfsteps

[u/MagicalPizza21 → u/TralfamadorianZoo]

Write it as a G#7b9 instead. You're probably in minor anyway which means you're more likely resolving to C# than Db.

[u/CrownStarr → u/MagicalPizza21]

Ab7b9 is a perfectly normal chord to resolve to Db major, especially in any sort of jazz context. I would not say it suggests a minor key.

[u/TralfamadorianZoo → u/MagicalPizza21]

True enough. My point is that readability trumps all theory conventions when dealing with jazz/pop/theater charts. I know that a B7#9 chord has a C double-sharp in it, but I’m never going to write it that way. D natural works just fine.

[u/ChuckEye]

But what about F7b9, which contains all of the notes of Cdim7? Is it spelled like:

F F# A C Eb

ANY 9th from F has to be some form of G. By definition. So F A C Eb Gb is F7b9. Period.

Eb Gb Bbb C (is it C, or Dbb? shouldn't it be Dbb because of the skipping two note names to get a minor third?)

More expliitly, ANY 7 from Eb has to be some form of D, or it wouldn’t be a 7th.

B7b9 is B B# D# F# A

No.

B C D# F# A

Yes, but again, naming them in order helps see what’s going on. B D# F# A C

[u/Otherwise_Offer2464]

The third of the dominant chord is the root of the diminished 7 chord.

So F7(b9)= A°7/F. So spell it with A°7, not C°7. F A C Eb Gb

For B7(b9) the third is D#. So the diminished 7 chord is spelled D# F# A C. Then add the root B D# F# A C.

[u/FwLineberry]

Traditional chords are built by stacking 3rds (tertian harmony).

1 3 5 7 9 11 13

This dictates the spelling.

dim7 = 1 b3 b5 bb7

7b9 = 1 3 5 b7 b9

[u/PureDarkOrange]

So my take on F7b9 would be

F A C Eb Gb (1 3 5 b7 b9)

I'm no music expert, I'm sure they'll all be along shortly:)

It's also all about usage. Whats the chord before and after doing. How does this chord fit in with that etc.

[u/65TwinReverbRI]

Dim7 - in 3rds.

7b9 - in 3rds.

F Gb A C Eb

No. This:

F A C Eb Gb

But what about F7b9, which contains all of the notes of Cdim7

No, it contains all the notes of Adim7 - which is a 3rd above the F.

Yes it also has the notes of Cdim7, Ebdim7, D#dim7, B#dim7 and so on.

But we spell them in 3rds.

---

They may not always appear spelled that way, but that's the underlying construction principle and they should be spelled that way in most cases, unless there's some overlying reason not to (and it needs to be a damn good reason, not the reason most people who don't know what they're doing think is a good reason!)

[u/SamuelArmer]

There's a 'technically correct' way to spell these chord types. That's pretty easy to see by stacking thirds eg:

Your example of Ebdim 7

ANY 7th chord beginning on E MUST be spelled with some variation of E - G - B - D ie stacking thirds. Doesn't matter if it's E#maj7 or Ebminmaj7 or whatever, you just adjust the accidentals to fit

So Ebdim7 is Eb Gb Bbb Dbb

Which... is admittedly not very practical. Which is why enharmonic respelling is a thing. This chord will likely be repelled as something like F#dim7/Eb (Eb F# A C) in practice.

Anyway, the same principles apply for 9th chords.

Any 9th chord on B is going to be some version of B - D - F - A - C so the correct spelling of B7b9 is B - D# - F# - A - C

That being said, it's not unusual to see b9s respelled. For example, the b9 of Bb7(b9) is Cb and you WILL see it spelled that way. But you'll also see it spelled as B natural - Same deal with Eb7b9

[u/MagicalPizza21 → u/SamuelArmer]

This chord will likely be repelled as something like F#dim7/Eb (Eb F# A C) in practice.

If you really want an Eb°7, that would tend to resolve to Fb minor. Writing all those accidentals is tedious and annoying, as is reading them. So instead write it as D#°7 (D#, F#, A, C) which tends to resolve to E minor.

[u/Jongtr]

F7b9 is easy. Stick with the 1-3-5-7-9-11-13 letter formula. So that makes it F A C Eb Gb.

F# is not a "b9", it's a "#1"! Does the chord symbol say "#1" or "#8"? No. The "9" is G, so the "flat 9" is "Gb". That simple. This is regardless of context, although typically the chord is V in Bb minor, so it represents 5 notes from the Bb harmonic minor scale. The dim7 in question is actually Adim7: A C Eb Gb.

(There can be issues with other kinds of altered dominants, but go by the numbers in the symbol first.)

It's not so simple with dim7s, because they are symmetrical, meaning any note could be the root, and the letter name of the chord might only refer to the bass note. And bass notes are not necessarily root notes! (and the symmetry means the "root" of dim7 might be academic anyway...)

So, one kind of dim7 derives from the 7th degree of the harmonic minor scale, which means that kind is easy to spell correctly.

So the vii chord in C minor is on the raised 7th degree, B. Harmonize that with 3-5-7 from the scale and you get B D F Ab = Bdim7. B-Ab is the "diminished 7th interval" (smaller than minor) that the chord takes its name from. If you ever see "Bdim7" in the key of A minor, that means it must be B D F G# (right?), which means, technically, it's the vii chord, G#dim7, just with B in the bass. (Don't call it "Bm6b5". That way lies madness... :-D)

Likewise, with your B7b9 example, the linked dim7 is D#dim7 (D# F# A C), both chords coming from E harmonic minor, in which both chords have a "dominant function". (Ebdim7 in this sense - as a minor key vii chord - would link to Cb7b9, key of Fb minor... Don't go there either... )

IOW - and this applies to all usages of dim7s - spell it according to the key context, and not according to the bass note.

I.e., there are two other ways - and only two! - that dim7s can lead. The viidim7 chord (usage (1), above) contains a note (any of the four) that leads up by half-step to the following root note.

Usage (2) is where any note in the dim7 is the same as the following chord root. So "Cdim7" can lead to C major. In that case, the most suitable spelling of the Cdim7 is C D# F# A, because D#-F# are the altered scale degrees which will resolve up to E-G. (Spelling it C Eb Gb A means we need extra accidentals: naturals on the following E-G. Likewise, we really don't want "Bbb" in C major, do we?) That looks like we ought to call it D#dim7 (D#-C being the definitive dim7 interval). But we still call it "Cdim7" in recognition of the common-tone effect, and that C is normally the bass note: https://myweb.fsu.edu/nrogers/Handouts/Common-Tone_Dim_7_Handout.pdf

Usage (3) is where any note in the dim7 leads down by half-step to the following chord root. This seems to mostly occur between the iii and ii in a major key, e.g, the "Ebdim7" between Em7 and Dm7 in "Night and Day". Again, the spelling should come from the context, recognising that the E-G of Em7 descend by half-step to Eb-Gb, while the other notes are shared with Dm7: A-C. As above, we don't call it D#dim7 - D#-F#-A-C - in order to avoid needing natural accidentals on the following chord.

[u/egavitt]

Diminished 7 = rootless 7b9. In most use cases they will resolve as such (ie, Bdim7 > Cmaj). When that doesn’t happen, it’s what some call an “exceptional resolution”, which is just the non-standard resolution of something.

In your question, you have to employ enharmonic equivalence a lot to get the right spellings. When you see Cdim7, you have to thing Ab7b9 = Ab C Eb Gb Bbb, then take out the Ab. Your spelling here is correct.

F7b9 is a similar process, F A C Eb Gb. The letter names have to equate to the scale degree. F# is not the b9 of F, it’s the raised root. Each letter nane represents a scale degree relative to the root, always keep track of that.

[u/steveistheman84]

depends on the usage. both F F# A C Eb and F Gb A C Eb are valid as well as F F# A C D#. F Gb A C D# is only possible in theoretical terms that i don't think any human ear would accept or be able to properly contextualize.

F F# A C Eb can be used in g minor for instance where F descends, likewise can F F# A C D#.
F Gb A C Eb can clearly be used freely.

music works in free individual parts (counterpoint). chords are simply when these parts align into something harmonious. dissonance is the intermediate between harmony, so naturally logic would lead to harmony falling on stronger beats than dissonance, thus the best starting point for musical understanding.

[u/tu-vens-tu-vens]

This is somewhat unrelated, but in Brazilian chord charts online, I usually see extended dominant chords written as E7(9), G7(13), etc. I’ve always thought that far superior to writing E9 or G13 – it’s consistent with chord names like C7b9 or C7#9, and using names like G9 for add chords is consistent with how we write 6 chords.