C#-alt7b13 Half-Diminished
The C#-alt7b13 chord is built from the notes C# – E – G – B – F##.
Piano sound loads on first tap.
Also known as
C#m7(b5)#11C#m7b5(#4)
Chord tones, one by one
C#Root
Root
The fundamental note the chord is built on — C#.
EThird
Minor third
Three semitones — makes the chord minor (darker, sadder).
GFifth
Diminished fifth (♭5)
Six semitones — a flat fifth. Creates instability, typical of m7♭5 and diminished chords.
BSeventh
Minor seventh (♭7)
Ten semitones — the dominant/minor seventh. Adds bluesy tension (7, m7).
F##Extension
Sharp eleventh (♯11)
A ♯11 — the bright, floating Lydian color.
🎼 Related scales
🎹 Modal analysis
This chord implies the Locrian scale; its characteristic note is the unstable ♭5.
🎸 Genres
Modern jazz · Post-bop · Fusion