In an earlier project we trained a network to learn the Coltrane changes, which is an important progression of jazz chords. Inside this network we discovered an interesting map, presented below, that leads from the root note of one chord to the root note of the next.
The map above has one intriguing property: its outer and inner rings of notes are examples of what we call strange circles. Each of these rings is a circle of major seconds; neighboring pitch classes on the ring are a major second, or two semitones, apart. For instance, A is a major second away from both B and G (the outer ring), while D is a major second away from both C and E (the inner ring).
One day the map above happened to be drawn on the chalkboard when I was in the lab with my ukulele in hand. I was noodling some minor chords, and was pleased by the sound of moving from D minor to A minor. As I played these two chords, I looked at the map on the board, and noticed how it lined up these two notes. Intrigued, I played other combinations of chords – for instance C minor and G minor – whose root notes were in similar relationships in the map. They too were pleasing. I then realized that a slight modified map would produce a new picture that I could use to guide me through a progression of twelve different chords. I drew the map, played its succession of chords, and I really liked the sound of the entire progression.
I created this new map by rotating the inner ring of notes to a different position, so that D was aligned with A, C was aligned with G, and so on. The new map that I created is given below:
The arrows on the map indicate how I use it to move from chord to chord. Let’s say I start with a D chord. The black arrow indicates that next an A chord will be played. The grey arrow shows that I next move counterclockwise to the second pair of chord roots, beginning with the inner ring (playing a C chord) and then moving to the outer ring (playing a G chord). I continue this pattern moving around the map, eventually returning to where I started, at the ‘D’ location of the inner ring.
One example of following this pattern is provided in the score below. This particular example plays major seventh chords at each map position, which has (to my ear at least) a pleasing, jazzy sound. The score uses ‘closed form chords’, which involve pressing a finger down on each ukulele string. So playing this score is an exercise in moving a closed form shape up and down the length of the fretboard. The Cmaj7 chord is formed at the very top of the fretboard, while the Bmaj7 is formed with the index finger barred across the 11th fret near the fretboard’s bottom. So, by following the new map one can perform a progression of chords that 1) uses each of the 12 possible roots in Western music, and 2) does so by covering the majority of the fretboard’s geometry.
The score above offers just a hint of the potential for using the map. Simple variations of the score involve replacing the major seventh chords with some other closed forms, such as the minor seventh (or major sixth), the dominant seventh, or the major. Of course, one could then use different chord types at different points in the score.
Another approach to varying the sound of the progression would be to follow a different route on the map – for instance going from the inner ring to the outer ring for the first pair of chords, but then going from the outer ring to the inner ring for the following pair of chords.
Another interesting approach would be to follow the same paths that are illustrated above, but to rotate the inner ring to a different position inside the outer one. For example, one clockwise twist of the inner ring would line up the D with the B, the C with the A, and so on. Changing the position of the inner ring would change the musical distance between successive chords, and as a result change the musicality of the progression.