C#-alt9 Minor 7th
The C#-alt9 chord is built from the notes C# – E – G# – B – D – D#.
Piano sound loads on first tap.
Chord tones, one by one
Root
The fundamental note the chord is built on — C#.
Minor third
Three semitones — makes the chord minor (darker, sadder).
Perfect fifth
Seven semitones — the most stable interval, reinforces the root.
Minor seventh (♭7)
Ten semitones — the dominant/minor seventh. Adds bluesy tension (7, m7).
Flat ninth (♭9)
A ♭9 — sharp, dissonant tension typical of altered dominant chords.
Ninth (9)
A 9th — colorful extension a whole step above the octave.
🎹 Modal analysis
This chord is so rich it doesn't fit a single scale: it's a polychord (an “upper structure”) that stacks tensions from several scales at once. It doesn't work like a dominant that “wants” to resolve — it's pure color: picture one triad floating over an unrelated bass, the kind of sound used in reharmonization and modal passages. To make sense of it, follow the note-by-note breakdown above.
🎸 Genres
Modern jazz · Fusion · Film & TV scoring · Impressionism