Sorry simple question but how do you avoid confusion when writing a chord like Bb13b9? It can be read as either B with a b13 and a b9 or Bb with a 13 and a b9. I suppose context but I am wondering if there is a formal way of writing these different chords for clarity?

Another confusing one is Gb13, is it a Gb with a 13 or a G with a b13?

Ps I found both examples while playing Naima. In this context it is a G melody note on a B chord so it is b13, although over a Bb pedal to add to the confusion, at least for me!


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    Another distinguishing factor is that if both the 9th and 13th are altered, the 9th should come before the 13th in the chord name. – user45266 Jun 6 '19 at 22:54

Bb13b9 can only be one thing, but that can be made more clear by using parentheses: Bb13(b9).

It is common to put altered extensions and added notes in parentheses at the end of a chord name. Also note that altered extensions are typically written in ascending order, so an altered B7 might look like B7(b9b13), or even B7b9b13, but rarely (if ever) B7b13b9, or even B7(b13b9).

In the absence of a 7th, with unaltered extensions, you might have Bb6/9, but a triad with added altered extensions would be pretty rare.

Similarly, Gb13 can only be one thing. A G chord with an added b13 would be notated explicitly as an added tone chord: G(addb13) or G(addEb). But G(addEb) would be an uncommon chord since altered extensions are usually added to seventh chords, but not to triads. So a Gb13 is just a G13 transposed down a half-step.

But, note that Gb13 is neither of the options suggested in the OP: "is it a Gb with a 13 or a G with a b13?" A G13 is a G7 with added 9th, 11th, and 13th extensions. It is very common to omit the 9th and 11th (and possibly the 5th), but the 7th and 13th must stay. So a G13 is at least G7 with an added 13 (E), and a Gb13 is at least Gb7 with and added 13 (Eb).

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To disambiguate (G♭)(13) from (G)(♭13), use superscripts: G♭13, G♭13.

Wikipedia shows examples like example. Here, the flat isn't superscripted, so what it modifies is the G. Even without the flat and the M7, the sharp is superscripted, so it modifies the 5 instead of the G.

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Superscript is the ideal, but...

But these pages...

...seem to show some kind of convention to use parentheses if for some reason superscript is not an option...

Bb + 13  => Bb(13)

Bb + b13 => Bb(b13) or just Bbb13

B  + 13  => B(13)   or just B13

B  + b13 => B(b13)

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    Personally, I'm a huge fan of parentheses. They're super useful: not only do I not have to write "add" every single time, I can also make my chord symbols easier to read, like you said. They also help the reader see the extensions as seprate from the underlying chord. – user45266 Jun 6 '19 at 22:51

Any time chord symbols are written like this, the first part is always the root. B♭9♭13 is always a 9♭13 chord built on the note B♭. If the composer wanted a B chord with a flat ninth, he/she would have made it clear, via "Badd♭9♭13" or "B(♭9♭13)". Makes sense because altered extensions must either come after some kind of natural extension (B7♭9, where the 7 separates the accidental automatically), or is notated with some kind of "add" or otherwise separated.

If there's an accidental after a note name, it modifies the root, not the following extension.

C♭9 versus C(♭9). Very different, but both are unambiguous.

Related: Most people I've met prefer altered extensions be listed from lowest to highest, e.g. A(9♯11♭13), not A(♭13♭9).

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  • I always see e.g. (add9) when adding chord tones to chords that don't contain a 7th. I don't think I've ever seen C(9) to indicate a C(add9), and I don't think I've ever seen a C(addb9) at all. Every time I see extensions in parentheses, they are altered extensions, and they belong to a 7th chord; or at least that is how it seems.... – ex nihilo Jun 6 '19 at 23:41
  • @DavidBowling Well, I see it a bunch. I think it's pretty useful, especially 'cos it saves me a lot of "add"s. – user45266 Jun 7 '19 at 4:00

While you can use parentheses and superscripts, there is one other option: include an implied chord tone.

A G(b13) implies a 9th (otherwise it would be G7b13 or G11b13). So you can also write it as G9b13. For B(b9b13), You can write B7b9b13.

This method always works. Either you'll have some sort of 7th, which doesn't use the accidentals -- there is no C(#7) chord, for example -- or you can use the word "add" -- as in Cadd9. (Granted, Caddb9 looks weird, but that's due to the b instead of a flat sign.)

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