Chromatic spectrum
The model in which musical octave meets color spectrum.

Sonic and electromagnetic waves have very different mediums as a carrier field. Sound is carried by air molecules, light travels through vacuum just because of ever present electromagnetic field.

But they're stil oscillations, so we an compare their frequencies and wavelenghts. But what to choose? Let's try both!

Frequency

Let's start with frequencies. What is 1 Hz? It's one oscillation per second. For EM it corresponds to radiation far in the long radio spectrum. We can't hear such slow air oscillations and 1 Hz is in infrasonic range.

This juxtaposition shows that electromagnetic and acoustic oscillations are of entirely different nature and can’t be matched just as they are. Audible frequencies of oscillating air correspond to long radio range of EM spectrum. If compared by the wavelengths our notes are situated somewhere around the FM radio range. In turn the visible light oscillations are so fast, that they can be matched only with hypersonic waves in some rigid bodies.

These oscillations are so short that they are comparable with the size of atoms in a crystal grid. The faster atoms move – the more heat they carry. A heated body starts to emit electromagnetic waves, starting from infrared and coming to the visible light range after about 1000K. So we can say, that sound and light are two main forms of oscillating energy propagation mechanics. And the similarities between them can be better justified not by their physical nature, but by the nature of human perception of them.

40th octave imaginary sound

Let take it mathematically. Acoustic oscillations frequency multiplies by to with every octave. This means we can find an imaginary pitch for any given frequency. This means we can find rythm notes and also it's another way to bring light and sound together.

Let's keep multiplying our A = 440 Hz by two until we reach the visible light spectrum – about 0.4–1 PHz. We can calculate all the notes frequencies and place them in the spectrogram. What we get is that A is near orange red, C is green and E is blue. Roughly. But If we consider a little lower base A frequency, we can see pretty nice corellation.

We can conclude that it's a fundamental property of our perception to close perceived parts of any spectrum into a seamless circle. And these circles are not just illusions as the resonances and periodicities are based on fundamental principles of physics.

Circle of colors and notes

A is the lowest frequency note and red is the lowest frequency color. It’s the starting point. Then we divide the light spectrum into 12 parts and get scientifically correspondent colors for every note in an octave. Now we can see the circle of musical intervals with our eyes and use it to remember all the musical semitones.