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C E D B Db F

Here are some attempts at naming this chord from four separate conversion web apps:

Dm9/13/C add(7)

Cmaj9 (11,b9)

Sorry, no matches found

CM11 (b9,add9)

I find it interesting how they each approach it differently, and wanted to see if someone else here has insight into which way is most 'correct' with no context for the chord.

There is one caveat, and that is I'm not interested in finding a better way of naming it by rearranging the note order, that's not the point of this question. The main point is I want to know how to handle adding an extension to a chord structure without removing the adjacent note to the extension. In this example it's the 9 and b9.

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    Chord symbols are a tool that humans use when communicating harmony-related information to other humans in real-life situations, and there are many communication-related considerations like what is relevant for the piece, the key and other chords around a symbol, and the knowledge and technical skills of the readers. Do you assume that chord symbols could be used for encoding any arbitrary note combination into a symbol from which the notes can be decoded back? For that, traditional music notation is better, because the chord can be written as-is, with notes and voicing and all. – piiperi Reinstate Monica May 24 at 9:26
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    The main point of the algorithm is to help people find the ideal spelling for their situation or taste. Secondary to that a feature will be added that allows them to play with different chord voicings based on templates that they make, or that others have made. This could then be transcribed into notation. However, as with any good piece of software, there must be a way of handling edge cases. That is the point of this question, so please don't take it as an affront to your notions of chord names being for human eyes only. – Numpy May 24 at 9:38
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    Better be careful that folk actually spell the makeup of their chords with the 'proper names' - C D# G might not come out as good old Cm! And, I'm sure you are aware, 'add' is very different from '+'. – Tim May 24 at 10:02
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    In this chord, you have four semitones crammed up next to each other so the system we typically use won't be the best fit to express it. You can always cram in a name by adding modifiers, but at a certain point modifiers don't really help express what's going. Without the Db it would easily be CM11 (no need to spell out the 9 it's implied). If you are trying to programmatically do this maybe look at concepts like prime form first which are the post tonal ways of classifying pitchs into what are known as pitch class sets. – Dom May 24 at 16:38
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    My preferred name for that chord is "tone cluster," but of the options presented in the question my favorite is "Sorry, no matches found." – phoog May 25 at 5:50
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Not every simultaneity of notes need be named as a chord. There are 924 possible 6-note selections from 12 notes. For this reason, I prefer to read traditional music notation rather than try to decode chord symbols (or for my own lead sheets, just write the melody, simple chords, major, minor, seventh, nineth, diminished, and the like; if something is more complex, I'd not use a lead sheet even in my shorthand stuff.)

However, this looks a bit like a polychord. There is a B06 (D-F-B) superimposed on a C9 with the fifth and seventh dropped (C-E-Db). However, combining incomplete chords may not describe what's happening harmonically.

Without seeing the context, it's hard to know what's happening musically. Note clusters (in equal temperament) can have more than one name. Take Ab-C-Eb-Gb: this is an Ab7-5, and Ab seventh with a flat fifth. It's rather common in classical music and moves nicely to Db-F-Ab (perhaps inverted), just a variant of a V-I. However if written as Ab-C-Eb-F#, it would normally resolve to G-C-Eb-G (or G-C-E-G) and then to G-B-D-G (or F) as a German Sixth. Sometimes (for various reasons or readability or carelessness) one will be written when the other is meant. It doesn't really matter too much. Chord usage, not chord names are what's important. That's why the key and context are needed to decode the music.

One may also have chords with non-harmonic tones so one could say this is a B diminished with three non-harmonic tone. Or even a D minor chord with the fifth omitted and a few non-harmonic tones.

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    Chord names can be important. At a (reading) gig, in key E, I encountered Abm. Couldn't find it anywhere on the guitar! Had it been written properly as G#m, I'd probably even expected it. – Tim May 24 at 17:12
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    Last I checked Ab-C-Eb-Gb was a garden variety dominant seventh chord with a perfect fifth. Also, enharmonic equivalence doesn't depend on equal temperament. – phoog May 25 at 5:54
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It's very easy to throw together a set of notes that, particularly out of musical context - have no 'correct' chord name. And it's easy to take a less random set and label it in several 'correct' ways.

Here's what the notation program Sibelius makes of your note set. It actually gives up without much of a fight, suggesting just two names. Neither of which, rather surprisingly, consider it as a C-rooted chord. I'd be more impressed had it had the confidence to report 'no useful name'.enter image description here

More interesting is what Sibelius makes of a rather more likely C-based quartal voicing. 13 possibilities, before looping back to its first shot.

I suggest you allow 'no useful name' as a result from your algorithm.

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  • I see sus9 and add4 shenanigans here. I would rather add an option to name the chord from your key of choice, and then provide the simplest name while showing the non-harmonic notes if it doesn't belong strictly to one key. – Numpy May 24 at 21:23
  • But chord names aren't key-dependent. – Laurence Payne May 24 at 22:19
  • Not strictly, no. But it will at least give the option to provide more context where previously there was none. There could be other contextual modifiers too. I'm reminded of a composer who notated many shell voicings of dominant 7th chords simply as dominant 7th chords. Even though he also strictly doesn't play the b7 – Numpy May 24 at 23:57

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