Phrygian

The note that defines it

D E♭ F G A B♭ C, then D. Compare with D natural minor, which has E. The flattened second is the most distinctive single interval in modal music, and it does more work than any other altered note.

The scale is the third mode of B♭ major and shares its two flats. Playing B♭ major from D produces it directly.

Raise the F to F♯ and the scale becomes the phrygian dominant — the flamenco scale proper. The two are often confused, and the plain mode is the darker and less ornamental of the pair.

On the fretboard

Tenth fret with the root on the low E string, or fifth fret with the root on the A. In drop-D tuning the open sixth string becomes the tonic and the E♭ sits one fret above it, which is why the mode is common in that tuning.

Alternating the open root with the note a semitone above is the entire foundation of the idiom — one finger and one open string produce it.

Where it is used

Metal and hard rock, where the semitone above an open tonic supplies menace at no harmonic cost. Flamenco uses the related phrygian dominant, which raises the third.

In jazz it appears over a iii chord, though rarely: the flattened second clashes with most standard voicings, and players who want that colour usually alter the chord instead.