C-alt7#9 Half-Diminished
The C-alt7#9 chord is built from the notes C – Eb – Gb – Bb – D#.
Piano sound loads on first tap.
Also known as
Caltadd#15Cm7#9b5Cm7b5#9
Chord tones, one by one
CRoot
Root
The fundamental note the chord is built on — C.
EbThird
Minor third
Three semitones — makes the chord minor (darker, sadder).
GbFifth
Diminished fifth (♭5)
Six semitones — a flat fifth. Creates instability, typical of m7♭5 and diminished chords.
BbSeventh
Minor seventh (♭7)
Ten semitones — the dominant/minor seventh. Adds bluesy tension (7, m7).
D#Extension
Sharp ninth (♯9)
A ♯9 — the gritty 'Hendrix' tension over a dominant chord.
🎼 Related scales
🎹 Modal analysis
This chord implies the Locrian scale; its characteristic note is the unstable ♭5.
🎸 Genres
Modern jazz · Post-bop · Fusion