Notation for sixth chords?

[fferri]

What notation could/should be used for sixth chords (i.e. added sixth chords)?

[gciruelos]

Not sure I get the question, something like ‘E6’ or ‘Em6’ works. Feel free to send a PR.

[fferri]

Of course new chord recipes could be added, but that's not the point.
In music theory chord extensions are modular (somewhat).
Some imply others (e.g. '9' implies '7').
Others can be added (e.g. 'add6') on top of others.
With the current system, all combinations should be written down as recipes.
But I think it would be simpler that way... any ideas?

[gciruelos]

I see. An idea: build a 'chord parser' that for example decomposes E9add6 into: ['E', '9', 'add6']. Then there are instructions about what this means: ['E'] means the major triad, ['9'] means the 7th and the 9th, ['add6'] means the 6th. I am open to other ideas.

[fferri]

I collected roughly all possible ways of writing chords (items on the same line are equivalent ways of writing the same chord):

Basic chord extensions and alterations:

• C CM Cmaj
• C- Cm Cmin
• Cdim Cº C-(♭5) Cm(♭5)
• Caug C+ C(♯5) CM(♯5)
• Csus4 Csus
• Csus2
• C7 Cdom7
• Cm7 Cmin/dom7
• Cmaj7 CΔ7 CΔ (although depending on context, Δ means only "major")
• Cmin/maj7 CmM7
• Cdim7 Cº7
• Cø7 Cm7(♭5)

Upper chord extensions

• C9 C7add9
• Cmaj9 Cmaj7add9
• C11
• C13

Add-on notation:

• C7(♯9)
• C11(♭13)
• C7sus4(omit5) C7sus4(no5)

Inversions and added bass:

• C/E
• C/A

Other:

• C5 (power chord)
• C6 Cadd6
• Cm6 Cm/add6 (note: it adds a major sixth)
• Cm(♭6) Cm/add♭6 (note: it adds a minor sixth)
• C69 Cadd6add9
• Calt Cdom7(♭9) Cdom7(♯9)

A few considerations:

• both C6 and Cadd6 do the same thing, however addN notation is more modular, as you could write Cadd6add9add13 but not C6913; it may make sense to have C69 as a recipe, while addN into a hypothetical parser, since addN can be used multiple times;
• still with addN, / seems necessary to make the chord more readable when the last letter is a letter, as in Cm/add6;
• addon notation (...) can be used to add tones (as in Cadd6) or alter existing tones (as in C(♯5) a.k.a. Caug);
• maybe there's more things which I haven't considered.