I want to have a key signature that has only the flats of Bb & Gb (I’m working with a Bb mode)

  • Why Gb? and not F#? If you have G-Dorian (1 flat) and construct a lead tone F# it will fit. Commented Apr 1, 2020 at 7:30
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    Could that 'Bb mode' be G minor? That could easily have Bb as m3, and need F# as the leading note. Decider may be - if you play some G notes, there probably won't be Gb, it'll be F#. Especially if you don't play any F nat. notes.
    – Tim
    Commented Apr 1, 2020 at 7:41
  • I'm on Tim's side. As Andrew says "I'm working ..." could you poste some measures of your piece or the final bars? Commented Apr 1, 2020 at 9:58
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    @Tim No. As I said I’m working with a Bb mode; in other words, Bb needs to be the tonic in order to achieve the sound I’m going for.
    – Andrew
    Commented Apr 1, 2020 at 17:36
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    "Be like Bartok" :-) Commented Apr 1, 2020 at 18:19

2 Answers 2


It's possible to just have Bb and Gb. Look at Bartok's Mikrokosmos for some examples. It may take some wrestling in your notation program (and may not be possible on free ones).

However, this is likely to be distracting, and the best way is probably to use a standard key signature corresponding to the closest tonality and use lots of accidentals. What you're doing sounds like an alteration of Bb major, so I would choose the standard two flats (Bb and Eb) and write E-naturals and Gbs as accidentals.

  • 5
    Another possibility (also slightly nonstandard) would be to us a single Bb (F major or D minor); then add the Gb when needed. The piece could cadence on the Bb. Ending on a non-key-signature-indicated-cadence isn't as distracting as remembering which irregular notes are changed. This may minimize the number of accidentals needed.
    – ttw
    Commented Apr 1, 2020 at 2:26
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    "It may take some wrestling in your notation program (and may not be possible on free ones)." Can you be more specific on how any notation program would get it done and why a program like Frescobaldi wouldn't be able to do the same thing?
    – Mast
    Commented Apr 1, 2020 at 13:01
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    On Musescore 3 (3.4.2) to make a custom key signature, go to Palettes (in the sidebar) > Key Signatures > More > Create Key Signature > (drag the accidentals to the staff in the dialog box) > Add > (close the dialog box) Then to add it to a score: Palettes > Key Signatures > More > (drag your custom key singature onto the score). Commented Apr 1, 2020 at 17:35
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    I'm not convinced - I find it easy enough to follow Bartok key signatures. Commented Apr 1, 2020 at 18:21

You try using a key signature of one flat for a basic Bb Lydian sound and then use Gb accidentals in the score.

If I understand where you are going with the tonality, it's like Lydian with a lowered sixth. Kind of Lydian on the bottom, but a harmonic tetrachord on the top of the scale.

The Gb flat in the score may be easier to read as it's reminder to not play G natural in what is otherwise a diatonic scale.

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