Overtone Scales

Each note, when played, has a series of overtones.

The notes have whole fractions of the wavelength of the fundamental, 1/2, 1/3rd, 1/4th, 1/5th, 1/6th etc.

The notes are, in descending order of strength:

Octave
Perfect 5th
Another octave
Major 3rd (slightly flat)
Another 5th
Another perfect 5th
Another octave
A major 9th

and so on. The b5 pops up later in the series. For the fine details see Wikipedia

Anyway, a dom7 chord is formed of the 1-3-5-b7 notes and they just happen to be the 4 strongest notes in the overtone scale, so the scale fits over it and can be used in improvisation.

The full overtone "scale" is similar to a mixture of the Lydian (1_2_3_#45_6_78) and Mixolydian (1_2_34_5_6b7_8), but has a #4 and a b5:

1_2_3_#45_6b7_8 or in steps WWWHWHW

Thanks. I think I've completely understand the usage of the overtone for improvisation over a dom7 chord. However, I am looking at my old lesson notebook and it says that there are two other ways to use it:

1.) Use over progressions that feature an altered IV7 chord

2.) Use the overtone scale a tritone away from the root in a progression ending with V7 - I. For example, G7 to Cmaj7 the overtone would start on Gb.

The first one kind of makes sense. Now the second one to me is unclear. I know the goal of the scale in that situation is to cause dissonance before resolving to the I chord, but why those notes? They are almost all the wrong notes over the V7. It seems like i could just play random notes and just hit the right ones on the I chord.

Tritone substitutions can give you some interesting changes... but I think either the book you're working from isn't really clear, or you're misunderstanding it.

The tritone you'd be using is from the root of the V chord, not the root of the key. In C, the V is G7, and up a tritone is C#. That would give you the overtones of C#-E#(F)-G#-B.

Tritone substitutions work because seventh chords contain a tritone between the 3 and b7; the tritone substitution has the same tension from the same notes:

G-B-D-F
C#-E#/F-G#-B

But the substitution is only for use over the dominant chord - when you come to I, you'd move a half step to resolve to C.

Ok, I see. That clears things up a bit. I've used tritone chord substitutions before, such as C#7 to replace G7 in a progression in C, but I never really did undertand the nature of the tritone.

The notes are, in descending order of strength:

Octave
Perfect 5th
Another octave
Major 3rd (slightly flat)
Another 5th
Another perfect 5th
Another octave
A major 9thI'll argue that the overtone major third (fifth harmonic) is a perfect major third. The equal temperament major third is quite sharp and caused great shock and offense to many accustomed to various just temperament systems when equal temperament was introduced.

The only intervals that are perfect under equal temperament are octaves. All others are compromised to a greater or lesser degree. The major third is the most out-of-tune interval in the system.