piano scale
C♯ double harmonic
C♯1D♭2E♯3F♯4G♯5A♭6B♯7
Two augmented seconds in one scale, one above the tonic and one below the octave.
The same sounds spelled from the other side are D♭ double harmonic.
Written out
Every accidental is written in, rather than left to a key signature, so the letters can be read one at a time.
The step pattern
C♯HDW+HE♯HF♯WG♯HAW+HB♯HC♯
What is true of it
C♯ double harmonic is C♯, D, E♯, F♯, G♯, A and B♯, and back to C♯.
Its steps are H – W+H – H – W – H – W+H – H, where W is a whole step and H a half.
On the same tonic, C♯ harmonic major differs from it by exactly one note.
Chords made only of these notes
C♯majorC♯augaugmentedC♯maj7major seventhDmajorDmminorDdimdiminishedD7dominant seventhDmaj7major seventh
Found by testing every chord in the catalogue against these 7 sounds, not chosen.
Other scales on C♯
C♯ Phrygian dominantexoticC♯ Lydian dominantexoticC♯ alteredexoticC♯ majormajorC♯ natural minorminorC♯ harmonic minorminor
C dbl harmD dbl harmD♯ dbl harmE♭ dbl harmE dbl harmF dbl harmF♯ dbl harmG♭ dbl harmall 374