A visual model for harmony theory

After we have laid the foundation of note names and intervals, I will now start to introduce a new harmony theory model which I will use extensively in future episodes. Using this model and SoundPrism you will be able to understand and apply harmony theory without any previous note knowledge and instrument skills.

The key related circle of thirds

The model is called  key related circle of thirds. It is shown in the next figure:


I could start to explain the circle and the things hidden within. Instead I think it is more important to learn how to play the model’s tones with an instrument.

Making the circle sound

The most simplest way to make music with the key related circle of thirds is SoundPrism, since its tone layout is directly based on that circle. This is the way the circle and SoundPrism are connected:

  1. Each of the black points in the key related circle of thirds corresponds to one of the horizontal rows in SoundPrism. The circle consists of seven points. SoundPrism consists of seven rows.
  2. The lowest point in the circle corresponds the lowest row in SoundPrism.
  3. The order of the points in the circle and the stripes in SoundPrism are the same. But in the circle the tones are arranged clockwise, in SoundPrism from bottom to the top.

Example 1:

In the following key related circle of thirds the lowest point is highlighted:


To play this tone you need to activate one tone mode first:


After that touch the lowest row because this row corresponds to the lowest tone in the key related circle of thirds:


It makes no difference on which horizontal position you are touching the row. One point in the key related circle of thirds does not only represent a single tone but also all of its octaves.

Example 2:

In the next example the lowest point and the clockwise neighbor is highlighted:


This means that you have to touch two rows at the same time, meaning the lowest row and the one above:


Example 3:

In this example the lowest point and the counterclockwise neighbouring tone are highlighted:


This means, that you have to touch the lowest and the highest row in SoundPrism. Logically these two tones are next to each other. But opposite to the key related circle of thirds SoundPrism does not represent that relationship:


Example 4

In this example three tones are highlighted, meaning the third, fourth and fifth tone:


That means you need to touch the third, fourth and fifth row in SoundPrism:


Wy not use SoundPrism directly?

Maybe you will wonder why I don’t use SoundPrism directly to explain harmony theory. Why is this tedious usage of the key related circle of thirds necessary?

The answer is, that there are many musical relationships and phenomena which don’t become apparent in SoundPrism but in the circular model. A previous version of SoundPrism did have a circular tone arrangement. But usability tests showed that such an version is harder to play. SoundPrism is optimized for playing, the key related circle of thirds for thinking and understanding.


The following video summarizes this blog post and provides additional examples.

Next episode

In the next episode I am going to extend the visual vocabulary introduced today additionally. Beside sequences of tones I will show how chords are represented within the circle of thirds and how the three tone mode of SoundPrism supports this.


  • The key related circle of thirds is a harmony model we are going to use to explain many harmony theory things in coming blog posts.
  • To understand future episodes, one needs to be able to read the key related circle and to translate into music.
  • SoundPrism is made for this since horizontal rows in SoundPrism correspond to tone points in the circle. The order of the tones in both SoundPrism and the circle is the same.
  • The key related circle of thirds arranges tones clockwise, SoundPrism arranges them vertically from the bottom to the top. Therefore the lowest row in SoundPrism corresponds to the lowest point in the key related circle of thirds.

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