Topic 2 How the chromaticcircleisbuilt

By constructing a regular dodecagon inscribed in a circle, twelve points are identified. These twelve points correspond to the twelve notes of our chromatic scale. The name of the notes is indicated by an internal disk that can rotate. In correspondence with each note a nail has been inserted which will serve as a pin for a rubber band which, by joining specific notes, will form geometric figures. Arranging the notes in a circle allows us to visually reproduce the cyclic nature of the scale which, as we have said, goes back to the start and repeats itself after a cycle of twelve semitones, just like the hands of a clock. Let’s see how it looks in the picture:

Let’s now give a first example of how the chromatic circle is used by representing the chromatic scale:

As you can see in the figure, the distance of a semitone between notes is represented by each side of the regular dodecagon: in fact, each side is equal to the other, just like each interval between one note and the next on the chromatic scale is always 1 semitone (sT). So:

1 side of the dodecagon = 1 semitone (sT)

Let us now see what the geometric representation of the major C scale is. We choose this scale because we all know it since we were children and it is the one which, as we have seen previously, is made up of these notes: C D E F G A B C. Did you know that, for this succession of notes to be defined as a major scale, it must follow a precise order of tones and semitones? Maybe not, and that’s why, thanks to the chromatic wheel, you will learn this construction rule very quickly and you will need it to build all the other major scales. All you need to do is join all the notes of the C scale with a rubber band, starting with the C note positioned at 12 o’clock and moving clockwise. Here is what you will get:

Thanks to the chromatic circle, we discover that the exact arrangement of tones and semitones that makes that succession of notes a major scale is the following:

T -T- sT– T- T- T sT

Where T = tone and sT = semitone.

The picture uses the traditional solf├ęge names for notes, which correspond to these in the British/American system: Do = C; Re = D; Mi = E; Fa = F; Sol = G; La = A; Si = B. Keep that in mind!

Now this succession of T and sT is a rule that must be followed to construct all major scales. Let’s try to build the G major scale. To make the task easier, turn the internal disc so as to position the note of G at 12 o’clock. You will be able to verify that, starting from G and proceeding clockwise until returning to the initial G, the series of T and sT will be identical to that of the C scale but the notes will have changed. Here is the sequence you will get:

G A B C D E F# G

As you can see, compared with the C scale, the G scale has an F#.

With the same procedure, try now to build the major scales of D, E, F, G, A, B. The only precaution you will have to have is to always use different names for the notes. Take the F scale, for example; at some point, you will find yourself having to decide whether to use the name A# or Bb. The correct answer is Bb because if you write:

F G A A# C D E F,

the A note (ignoring the #) is mentioned twice. If instead we rename A# as Bb (same pitch but different name) we will have named all the sounds of this scale correctly.