Do the key signatures C-flat minor/G-flat minor exist? If yes,what notes are used in them, and they are rarely or frequently used in classical music?

Also: DO these keys exist 9((not theorethical) in songs with half semitone scales (i.e. xenharmonic music)?

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    Pretty pointless, as Bm and F#m are far easier to write, read. In 12tet, if that makes any difference. – Tim Dec 15 '19 at 20:03
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    But there also other key signatures that sound identical: D-sharp major, A-sharp major, B-sharp major, B-sharp minor, G-sharp major, e-sharp major, etc... Do you think that they should have different pitch when using a scale with more than 12 notes per octave? – TechnicGoblin5R Dec 15 '19 at 20:07
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    @Tim they are the same in any twelve-tone temperament. That is, the reason (for example) E♭ and D♯ are the same is that there is only one key available to serve for both. Whether or not the distance from D to that key is the same as the distance from that key to E makes no difference. – phoog Dec 15 '19 at 20:17
  • This thread isn't really a duplicate of the aforementioned older thread. The most abstruse key the older question mentioned is A♭ minor; not only does this have a key signature (7 flats), there are real pieces which use it. By contrast, G♭ minor and C♭ minor are too abstruse for conventional key signatures. Even those keys would only be met in passing, even then only if the composer refused to do an enharmonic change (such a change would give an easier key of F# minor or B minor), and even then no such key signature would be used. – Rosie F Dec 16 '19 at 17:41

Do the key signatures C-flat minor/G-flat minor exist?

Theoretically, they can be said to exist, but since these keys are the relative minor keys of E♭♭ major and B♭♭ major, respectively, the key signatures involve double flats. They are impractical and weird. Furthermore, they are (on any 12-tone keyboard) enharmonically equivalent to B minor and F♯ minor, respectively, so there's really no point in using them.

If yes, what notes are used in them?

C♭ natural minor: C♭, D♭, E♭♭, F♭, G♭, A♭♭, B♭♭
C♭ harmonic minor: C♭, D♭, E♭♭, F♭, G♭, A♭♭, B♭
C♭ melodic minor (ascending): C♭, D♭, E♭♭, F♭, G♭, A♭, B♭

G♭ natural minor: G♭, A♭, B♭♭, C♭, D♭, E♭♭, F♭
G♭ harmonic minor: G♭, A♭, B♭♭, C♭, D♭, E♭♭, F
G♭ melodic minor (ascending): G♭, A♭, B♭♭, C♭, D♭, E♭, F

The descending melodic minor scales are the same as the natural minor.

Are they rarely or frequently used in classical music?

They are certainly extremely rare in classical music. In fact, I would be very surprised if they have ever been used at all.

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Answer for the xenharmonic part:

In some scales, they definitely do exist. For example, consider the 19-TET, where G♭ is a note on its own, which is different from F♯ (C♭ is also a different note, but now it's enharmonic with H♯, not H♮ as in 12-TET). So, G♭ minor and C♭ minor are "normal" keys in 19-TET, despite their key signatures have double accidentals (9 and 10 flats respectively — but since only the scales which have the same number of accidentals* modulo 19 are enharmonically equivalent in 19-TET, so in order to represent all 19 possible (sounding) classes of keys one has to use key signatures with at least 9 (or 10) accidentals).

*Number of accidentals is meant to be positive for sharps and negative for flats

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  • By the way, H is the German nomenclature for B♮ in English nomenclature. – awe lotta Jul 7 at 15:04

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