Sus b9 (shell)

Notes and formula

The formula is 0 – 1 – 5 in semitones. The second is lowered to a semitone above the root, and the fourth sits above it.

There is no third and no fifth. What identifies the chord is the semitone at the bottom — the interval that separates Phrygian from every other minor mode.

Why the semitone is the whole chord

A lowered second above a root is the most recognisable interval in modal music. It is what makes flamenco sound Spanish, what makes Phrygian passages sound Middle Eastern to Western ears, and what a single chord can state without any melody at all.

Everything else in the chord is support. Add a fifth and the sound is unchanged; add a third and the mode is still Phrygian, just less exposed.

How to play it

On guitar the shape is x–3–3–x–2–x, sounding C–F–D♭. Spreading the semitone across two octaves is what makes the chord usable — struck as a close cluster it simply sounds wrong.

On piano the same rule applies more strictly: keep the D♭ well above the C, or the chord reads as a mistake.

Where it belongs

In flamenco and in everything derived from it, where the descending Andalusian cadence lands on a chord with exactly this colour. In film scoring, as shorthand for a place the composer wants to sound distant.

It also appears in metal, where Phrygian riffs are standard and the semitone above the root is a defining sound of the genre.

Against the ordinary suspensions

Csus2 uses a natural second and sounds open. Csus4 uses the fourth and leans. This chord uses a lowered second and sounds neither open nor leaning — it sounds modal, which is a different axis entirely.

The three chords are related only by having no third. What they do with the space is completely different.

Frequently asked questions