C Dominant seventh sharp ninth

The 7♯9 dominant is one of the most iconic altered dominant sounds in blues and jazz language. It preserves strong V function, but adds a rough, vocal-like upper tension that feels urgent and expressive. This sonority is often heard as both aggressive and soulful.

Construction

Practical formula: 1-3-5-♭7-♯9. In C: C-E-G-B♭-D♯. Function remains clear through 3 and ♭7; ♯9 introduces the characteristic frictional edge.

Usage

Use 7♯9 in blues turnarounds, jazz dominant lines, rock/funk dominant riffs, and dramatic transition points. It is ideal when a plain dominant is too polite and a denser altered stack is unnecessary.

Examples

• Classic V7♯9 in blues resolution movement
• Jazz comping with expressive altered dominant bite
• Rock/funk dominant accents with gritty color

Play

Keep guide tones stable, then voice ♯9 where it is clearly audible. Avoid overstacking inner tones so the chord keeps punch and definition.

Ear-training cues

Compared with 7, this sounds immediately rougher and more vocal. The ♯9 creates a "blue-note" tension against the dominant body.