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Guitar Theory:
Pitch Axis Theory and Modal Harmony


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Q: I have been searching for a good lesson about a concept called Pitch Axis Theory, but I cannot find one that explains how to use it. Most of the stuff I’ve found just goes on about Modes, but doesn’t really cover how the shredder guys and the fusion guys actually use this concept musically. Can you please do a lesson about this topic I really want to know more about it!
Thanks, Joey - New York, NY.

A: Hi Joey, thanks for your question, this topic is quite simply really. Pitch Axis or whats often called Modal Playing is all about droning bass notes and also supplemental harmonies being played which in turn influence the use of certain scale types.

For example, imagine if I were to play a constant D bass tone. And, under that I played an F Major chord for 8 beats. Then, I switched over to a Gb Diminished chord for 8 beats. What scales would I have to play in order to make melodies over this four bar progression?

Under that bass D tone, the F Major chord would harmonize out to become a D Mi7 chord. This would support the use of D Natural Minor (AEOLIAN) scale. However, the appearance of that Gb Diminished chord under the D bass tone harmonizes out to generate the sound of D7 chord. The scale which fits well over that chord structure is the Mixolydian Mode.

Key of D Modal

In the improvisation I performed at the start of the video lesson there were four chords which generated four unique harmonies for me to switch scale types over. Look at the chord chart below:

Modal Pitch Axis Jam from the Video:

In the first two bars the Lydian mode works well to highlight the G# tone found as the #11 degree of the chord. When playing lines, work at pushing into the G# to bring out the color of that chord. In measures 3 and 4 the tonality shifts to Dominant 7th color. The Mixolydian mode works well here. Lean into F# and C notes for bringing out the new color of the Dominant sounds. In line two bars 5 and 6 we introduce a flat 3rd and flat 6th interval on that D bass tone. The effect is pure Natural Minor (Aeolian) scale. Lean into those minor 3rd and 6th (F and Bb) tones. Our final harmony shift is to the Major scale on measures seven and eight.