Writing Melodies in the Gb Mixolydian Mode
Gb Mixolydian is a major scale with one note lowered by a half step: the seventh. That small change takes the polished, everything-resolves sound of a major key and gives it a looser, bluesier swagger. Its seven notes are Gb, Ab, Bb, Cb, Db, Eb, Fb. Six of them behave much like a major scale. The seventh, Fb, is where the attitude comes from, and learning to use it well is most of the craft of writing in this mode.
Seven Notes, Seven Letters
The first thing you notice is the spelling. Cb and Fb look odd on paper, so here's the reasoning. Written music uses each letter name, A through G, exactly once in a scale. Starting on Gb and working up, you need some kind of A, B, C, D, E and F. The notes that fit the sound happen to be Cb and Fb. On a piano, Cb is the white key you'd normally call B, and Fb is the white key you'd normally call E. They're the same keys, just named to keep the letters in order.
That gives the scale a key signature of 7 flats, which is every note flatted. A key signature is the set of sharps or flats written at the start of each line of music so you don't have to mark them on every note. Gb Mixolydian borrows its signature from Cb major (Cb, Db, Eb, Fb, Gb, Ab, Bb). Same notes, but Cb major treats Cb as home, while Gb Mixolydian treats Gb as home.
Seven flats is a lot to read, and that's why most musicians write this sound as F# Mixolydian, with a key signature of 5 sharps. It sounds exactly the same. If a chart hands you F# Mixolydian, you already know this scale. Gb is simply the less common spelling, and it's completely correct.
How the Steps Build It
A whole step (W) is a jump of two piano keys, skipping one in between. A half step (H) is the smallest move in Western music, from one key to the very next. Mixolydian follows this pattern: W - W - H - W - W - H - W.
From Gb: a whole step to Ab, a whole step to Bb, a half step to Cb, a whole step to Db, a whole step to Eb, a half step to Fb, and a whole step back up to Gb. Compare it with a regular major scale and only one thing differs: the last two steps are flipped. In major, the seventh note sits just a half step below the root and leans hard into it. Here the seventh sits a whole step below, so it doesn't lean. It hangs back.
In terms of intervals (the distance of each note from the root), the formula is 1, 2, 3, 4, 5, 6, b7: a major 2nd, major 3rd, perfect 4th, perfect 5th, major 6th and a minor 7th.
Which Notes Feel Like Home
Think of the notes as having different jobs in a melody.
- Resting notes: Gb, Bb and Db. Together they make the Gb major chord, and a phrase that lands on any of them sounds settled. Gb is the most final; Bb and Db feel like a comma rather than a full stop.
- Moving notes: Ab, Cb and Eb. These want to step somewhere. Cb especially likes to fall a half step to Bb. Ab drifts to Gb or Bb.
- The character note: Fb. This is the flat 7th, and it's the one you hear in this mode and nowhere in plain Gb major. Fb tends to fall a half step to Eb, or sit below the root and jump up to Gb. Either way it says "this isn't ordinary major" the moment it sounds.
Sing up from Gb to Fb and stop. You'll feel the pull to finish, but it's gentler than in a major scale. That relaxed pull is the Mixolydian sound in miniature, and it's why the mode turns up so often in blues-rock, folk, Celtic fiddle tunes and riff-based rock.
The Chords Under Your Tune
Stack every other note of the scale and you get these chords:
- I: Gb (Gb-Bb-Db) / Gb7
- ii: Abm (Ab-Cb-Eb) / Abm7
- iii°: Bbdim (Bb-Db-Fb) / Bbm7b5
- IV: Cb (Cb-Eb-Gb) / Cbmaj7
- v: Dbm (Db-Fb-Ab) / Dbm7
- vi: Ebm (Eb-Gb-Bb) / Ebm7
- bVII: Fb (Fb-Ab-Cb) / Fbmaj7
Notice the home chord's seventh version is Gb7, a dominant seventh, which has a bluesy edge all on its own. Notice too that the v chord is minor (Dbm) and that there's a major chord built on the flat 7th: Fb. Those two chords carry the Fb note and give the mode its color.
The classic Mixolydian move is Gb - Fb - Cb - Gb (I - bVII - IV - I). Play it slowly on piano and listen to how Fb steps down to Cb and back home without ever needing a dramatic leading tone. It sounds open and a little rough-edged, in the best way.
Writing a Four-Bar Tune
Here's a sketch over that progression, one bar per chord:
- Over Gb: Gb, Ab, Bb, Db. Climb from home through the chord.
- Over Fb: Eb, Fb, Eb, Db. Lean on Fb so the ear hears the flat 7th clearly.
- Over Cb: Cb, Bb, Ab, Bb. Let Cb fall to Bb, its natural resting spot.
- Over Gb: drop to the Fb below, then up to Gb, and hold it.
That final low-Fb-to-Gb move is a signature Mixolydian cadence. A major scale would approach the root from a half step below; this one approaches from a whole step, and the difference is instantly recognisable.
For Guitarists
Your Gb roots sit on the low E string at frets 2 and 14, and on the A string at frets 9 and 21. The 2nd-fret root is the comfortable starting point: play the four-bar tune above beginning there, and you'll find Fb a whole step below your root, two frets back on the same string.
Try This
Record yourself holding a Gb drone or strumming Gb7 for a minute. Over it, sing or play the tune above, then change only the last bar so the phrase ends on Fb instead of Gb. Listen to how unfinished it feels, then write a second four bars that answers it by landing on Gb.
For the bigger picture, read The Mixolydian Mode.