Where Oscilloscope Music's Chords Come From
Oscilloscope music's chords come from copying a shape. Drawing the same figure N times per cycle puts a component at N times the frequency into the signal, so N copies on screen is an N:1 ratio and a real musical interval. Exact whole-number ratios are also the only ones that hold still on screen, which pushes the genre toward just intonation.
Hi, I'm Trina with BeamTracer.com — today it's where oscilloscope music's harmony actually comes from, and why it fights your piano's tuning.
Here is the fact that reorganises everything else about oscilloscope music:
If you draw the same shape twice on the screen instead of once, you have played an octave.
Not "it sounds a bit like" an octave. It is one. The copy is a real musical interval, and you can hear it. Draw the shape three times and you get a fifth plus an octave. Five times, a major third plus two octaves. The number of copies on screen and the chord in your ears are the same number.
Where do oscilloscope music's chords come from?
- On an XY display, the two audio channels are not "sound with a picture attached." The left channel is the horizontal position of the beam and the right channel is the vertical position. The picture is the sound.
- Drawing one shape at several places on screen means its waveform repeats several times per cycle. Repeating a waveform N times per cycle puts a component at N times the frequency into the signal.
- An exact whole-number frequency ratio is what we call an interval. So N copies of a shape = an N:1 ratio = a chord. Oscilloscope artists call this trick the duplicator.
- Whole-number ratios also happen to be the only ones that hold still on screen. That is why the genre gravitates toward just intonation rather than the equal temperament your keyboard is tuned to.
Why is a copied shape the same thing as a chord?
Look at this figure. It is one loop, drawn five times around a circle.
The beam does not jump between five separate objects. It travels one continuous path that happens to trace the same loop five times per lap. Because the loop repeats five times inside one full cycle, the signal that draws it contains something moving five times as fast as the cycle itself — a 5:1 relationship between the two motions.
That is exactly what a musical interval is: two frequencies locked in a small whole-number ratio. The reason a chord sounds like one thing rather than two is that the parts line up periodically. On a scope you get to watch them line up. Harmony is literally resonance, and this is the one place where you can see it happening.
It also solves the medium's hardest problem. You normally cannot play two sounds at once on an oscilloscope — add a second signal to the first and the beam draws neither shape, it draws the sum, which is usually a blob. Duplication is the exception. Because the copies are the same shape at a locked ratio, the image stays legible while two pitches genuinely coexist.
| Copies on screen | Frequency ratio | What you hear |
|---|---|---|
| 2 | 2:1 | An octave |
| 3 | 3:1 | A fifth, plus an octave |
| 4 | 4:1 | Two octaves |
| 5 | 5:1 | A major third, plus two octaves |
How do I set a frequency ratio in OSC-1?
You do not need a duplicator to hear this relationship. Any two whole numbers driving the horizontal and vertical axes will do it. In BeamTracer's OSC-1 oscilloscope, the Lissajous generator has a Freq X and a Freq Y control and prints the ratio back to you as you move them.
Set Freq X to 3 and Freq Y to 2 and the readout says Ratio: 3:2 — a perfect fifth, drawn. Then walk through the family:
- 2:1 — an octave. The simplest stable figure there is.
- 3:2 — a perfect fifth (the picture at the top of this article).
- 5:4 — a major third. Busier, still stable.
- 7:5 — not a classical interval at all. Legible, but restless.
Here is that walk with the ratio live, which is the part a photograph cannot carry:
Freq X and Freq Y moving through 3:2, 5:4 and 7:5 and back. Each exact whole-number ratio settles into a figure that holds still; the picture only churns while the two frequencies are on their way from one ratio to the next.
Count the lobes along one edge and you have read the ratio off the screen. That is the whole trick behind Lissajous figures, and it is a century older than the oscilloscope — Jules Antoine Lissajous described the figures in his 1857 Mémoire sur l'étude optique des mouvements vibratoires.
The same logic applies when you play the built-in synthesizer. Octaves and fifths give clean, readable figures; complicated ratios give shapes that are interesting but hard to predict. It is the one case in music where "simple interval" and "clean picture" are the same statement.
Why does oscilloscope music use just intonation?
Here is the part that catches people out.
A figure holds still only when the ratio between its frequencies is exactly a whole-number ratio. Not nearly. Exactly. If the ratio is slightly off, the figure slowly rotates or churns — the drift rate is the size of the error.
Twelve-tone equal temperament, the tuning nearly every keyboard, guitar and recorded track uses, is built on approximations of those ratios. It spreads the error evenly so you can play in any key. The cost, on a scope:
- A fifth in equal temperament is off by about 0.1%. Nearly stable — the figure creeps.
- A major third is off by about 0.8%. Visibly unstable. It will not sit still.
- In chords of three or more notes, the errors stack. What holds as an interval falls apart as a triad.
Neither percentage is folklore — both fall straight out of the tuning math. An equal-tempered fifth is 2^(7/12) ≈ 1.4983 against a just 3:2 = 1.5, and an equal-tempered major third is 2^(4/12) ≈ 1.2599 against a just 5:4 = 1.25. Divide them yourself and you get the 0.1% and 0.8%.
So oscilloscope composers reach for just intonation — tuning built from exact whole-number ratios — because it is what the display rewards. Under just intonation the figure locks. Under equal temperament it wobbles.
| Just intonation | 12-tone equal temperament | |
|---|---|---|
| Octaves hold still | Yes | Yes |
| Fifths hold still | Yes | Partial — a slow drift |
| Major thirds hold still | Yes | No |
| Triads and bigger chords hold still | Yes | No |
| Plays in tune with a piano or a released track | Partial | Yes |
| Can change key freely | Partial | Yes |
Neither column is “correct”
They are optimised for different things — one for still images, one for playing with everyone else. Which you want depends on whether the picture or the mix is the thing that has to hold together.
How do I play along with 12-TET instruments?
If you want your visuals to lock and you have to sit in a mix with instruments in standard tuning, these are the moves that actually work:
- Spend your stability budget on octaves and fifths. They are the intervals equal temperament gets closest to, so they are the ones that stay readable in a normal-tuned arrangement.
- Do not build the visual on thirds. A major third is the interval equal temperament misses by the most, and it is the one you will watch smear.
- Retune only the part that is drawing. The pad, the bass and the drums can stay in standard tuning; the voice that owns the picture is the one that needs exact ratios.
- Use the drift on purpose. A tiny, deliberate detune sets a figure slowly rotating. Handled as a decision instead of an accident, that is one of the best-looking moves in the medium.
- Watch, do not calculate. Move the ratio and look at the screen. Stable versus churning is obvious in about a second, which is faster than any theory.
The honest caveat
Fully adopting just intonation in a normal production workflow takes real effort. Most people end up somewhere in between — a strict tuning for the voice that draws, standard tuning for everything else.
What does this change about how you compose?
Once you see a copied shape as a chord, the two halves of oscilloscope music stop being separate crafts. Adding a voice and adding a copy are the same action. Tightening a tuning and steadying an image are the same action. You are not composing music and then visualising it — you are composing one thing that arrives in two senses.
New to drawing with an audio signal? Start with the oscilloscope music guide, which covers why the beam behaves the way it does. If you would rather bring a shape in than derive one, the guide to converting a 3D model to oscilloscope art picks up there. And the audio sources documentation walks through the Lissajous generator controls used above.
See a chord instead of hearing it — free, no account required
OPEN OSC-1 OSCILLOSCOPE →One signal, two senses. beamtracer.com — I'll see you in the next one.