C sharp suspended fourth flat ninth

The sus4 ♭9 chord replaces the third with a perfect fourth above the root and adds a lowered ninth. Without a major or minor third in the voicing, it reads as dominant-function color with a dark, Spanish-Phrygian edge: the ♭9 rubs against the root while the fourth keeps the harmony open and unresolved until you move to a chord with a third.

Construction

Core tones: 1-4-♭9 (often with ♭7 present in extended voicings). In C7sus(♭9), think C-F-D♭ as a skeletal color set, with bass and context supplying dominant function.

Usage

Classic on V resolving to minor or major, in Latin and flamenco-influenced progressions, and in modern jazz as a tense dominant substitute before resolution.

Examples

• Spanish cadences and Phrygian dominant contexts
• Modal jazz tunes that emphasize ♭2 color over a dominant pedal
• Film scoring for exotic or ominous dominant pads

Play

Keep the sus fourth clear, separate root and ♭9 when possible, and resolve the sus by dropping the fourth to the third of the target chord.

Ear-training cues

Hear no third, a perfect fourth above the root, and a minor second between root and ♭9.