The fifth mode of the Melodic Minor Scale is called the Mixolydian b6. It is exactly what it says on the tin, A Mixolydian mode with the 6th degree lowered one semitone. Why? Well, I'm not sure when you'd use this one, I must find out if any of my friends have ever used it in 'real life', I don't like the sound of it over dominant chords, the 5 and #5 (same as b6) just don't get along most times and it just sounds sour to me.

The scale formula for the Mixolydian b6 is below, it describes the interval distances between each note of the scale. Note the 4 Tones in a row that help give this scale it's unique quality.

	T		T		S		T		S		T		T
1		2		3		4		5		6		7		8

T = Tone [whole step] • S = Semitone [half step]

Comparison With Major Scale

Scales are always compared to the Major Scale to find the intervals used.

	I	II	III	IV	V	VI	VII	I
C Major Scale	C	D	E	F	G	A	B	C
C Lydian Dominant	C	D	E	F	G	Ab	Bb	C
Equation	1	2	3	4	5	b6	b7	1

As the name suggests it's easiest to think of this as a Mixolydian Mode with a flat 6 (b6).

Chords And Extensions

Because we're thinking modally here we're looking at the individual chords you might use this scale over not the Chords In The Key of the Melodic Minor Scale.

This scale is played over something I guess... one would assume Dominant chords with a flat 13 (b13) but that's usually functioning as an 'alteration' which would make it a #5 (same note as a b6) and you'd use a different scale there.

The obvious answer would be some kind of pedal where you have the Modal root as a pedal note in the bass and you explore chords (and solos) over it using notes from the parent Melodic Minor scale - the kind of thing serious modern jazz fusion cats might get off on but beyond my interest in that kind of thing!