How to Draw Two Things at Once on an Oscilloscope

An XY oscilloscope has one beam it can never lift, so two objects can only mean the beam taking turns fast enough for your eye to fuse them. The reliable method is phase cutting: in BeamTracer's OSC-1 oscilloscope, COPIES in the SHAPE MORPH panel slices each trace cycle so one stereo signal draws several complete, independent figures.

Hi, I'm Trina with BeamTracer.com — this one's about getting two separate objects out of an instrument that only has one beam.

You have a circle. You're pleased with the circle. Now you want a second circle next to it — a moon beside a planet, two eyes in a face, a bass shape and a lead shape moving independently.

So you play both signals at once. And you get one strange new object that is neither of them.

This isn't a mistake you made. It's the central constraint of the entire medium, and every oscilloscope artist runs into it in their first hour.

Can an oscilloscope really draw two separate objects?

An XY oscilloscope has one beam, and — unlike a pen plotter or a computer screen — it can never lift that beam off the paper. There is no pen-up. Whatever your two channels say at a given instant, the beam is at exactly one place.

So "two objects" can only ever mean one of two things:

• The beam takes turns. It draws object A, jumps, draws object B, jumps back, fast enough that your eye fuses them into two steady pictures.
• You gate the beam off while it travels between them, using a third channel your stereo file cannot carry.

What it can never mean is "play both signals simultaneously". Adding two signals does not stack two pictures — it produces a third picture.

Why does adding two signals fail?

Because the beam follows the sum, and the sum is a new path. Here is a circle: one clean loop, the left channel tracing X and the right channel tracing Y.

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Now add a second, smaller circle to it — one that goes round five times for every one lap of the big circle. Both signals are simple. Both are circles. Playing them together gives this:

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Not two circles. One four-lobed figure that neither signal contains.

Which is a lovely shape, and completely useless if what you wanted was two circles. The two signals added together, sample by sample, and the beam followed the sum. That is what mixing does: it makes a new path, not a layered image.

There are four established answers to that problem, and they escalate in cleverness.

How do you blank the beam with a third channel?

Some oscilloscopes have a Z input on the back, which controls beam brightness independently of position. Feed it a third signal and you can switch the beam off while it travels from object A to object B. Genuinely two objects, cleanly separated, no distortion of the picture.

Two drawbacks, and they are serious. First, a stereo release only has two channels, so nobody else's scope will ever reproduce your third one — your piece plays back wrong everywhere but your own bench. Second, and more subtly: the gating is not audible. The picture changes in a way the music does not, which breaks the one-to-one relationship between what you hear and what you see that makes this art form worth doing.

How do you offset the whole figure with a square wave?

Add a square wave to both channels and the entire figure jumps between two positions. If it jumps fast enough, your eye stops seeing a jump and starts seeing two copies.

This works, it needs no third channel, and it is easy to reason about. It also gets expensive fast:

• Every extra square wave doubles the number of copies.
• Each one has to run at half the frequency of the one before it.
• The slowest one still has to stay above roughly 30 Hz or the whole thing flickers, and the fastest is capped by the file's own frequency ceiling.

Four objects is comfortable. Sixteen is not.

How do you draw fast and step through a list of positions?

Instead of square waves, draw the object at a high rate and step through a list of positions at a low rate. Position one, draw the object; position two, draw it again; and so on.

The cost is the one from the sample rate article: a high drawing frequency pushes the harmonics that sharpen your corners above the Nyquist limit, so every object gets softer as you add more of them. Ten crisp objects and thirty mushy ones are the same budget spent differently.

What is phase cutting, and why does it actually solve the problem?

Phase cutting is the one I'd learn first — it keeps the picture sharp, needs no third channel, and survives a stereo bounce.

Everything you draw is ultimately driven by a phase — a value that ramps smoothly from 0 to 1 over and over, and which the shape's equations turn into positions. One lap of the phase is one lap of the figure.

Phase cutting takes that single ramp and cuts it into pieces. Cut it in half: the first half of every lap becomes its own complete 0-to-1 ramp, and so does the second half. Now feed a different object into each piece. In one cycle the beam draws object A from start to finish, then draws object B from start to finish, then repeats — and because that happens tens of times per second, you see two whole, separate, independent objects.

Three things separate it from a plain switch:

• Cuts do not have to be equal. Weight them and a complex object can get 70% of the cycle while a simple one gets 30% — which is also a brightness control, since a beam that spends longer somewhere makes it brighter.
• Cuts can crossfade. Blend between a hard cut and a smooth one and objects morph into each other instead of switching.
• You get a frequency hierarchy for free. There is a master rate at which the whole set of cuts is traversed, and a rate inside each cut. That is precisely the structure music already has, so the visual arrangement and the musical arrangement stay locked together.

And critically: it's all still just two channels. It survives being bounced to a stereo file, uploaded, and played on someone else's scope, exactly as you heard it.

How do the four methods compare?

The last column is the one most people underrate. If the way you separate two objects is inaudible, you have made a video with a soundtrack. If it is audible, you have made oscilloscope music.

How do you draw several objects at once in BeamTracer OSC-1?

COPIES in the SHAPE MORPH panel is phase cutting, shipped. Set it to 3 and you get three complete, independent figures from the same single stereo signal — not one figure repeated by an effect, but the beam genuinely drawing each one in its own slice of every cycle.

Two things are worth watching for as you raise COPIES. The panel names the musical interval the copies produce — three copies is a fifth plus an octave, and you can hear it arrive as you set it, which is the subject of where oscilloscope music's chords come from. And the panel shows how often each individual copy is being redrawn, with a warning when that figure drops near 30 Hz. Copies divide a fixed amount of beam time between them, so the flicker floor from the square-wave method is still there — phase cutting spends the budget far better, it does not abolish it.

The stereo signal still carries travel between copies: the beam has to get from the end of one object to the start of the next. OSC-1's VECTOR DISPLAY and AMBER CRT presets hide those connector spans automatically; a hardware scope still receives the original stereo journey. That is the exact limitation the laser section below lifts with a real blanking channel.

Is OSC-1 free, and does it need an install?

OSC-1 is free to open, requires no account, and installs nothing — COPIES, the built-in 3D arrangements and the MIXER are all reachable in a browser tab. The honest catch is the browser: OSC-1 needs Chrome or Edge, on any operating system.

How does OSC-1 trace several separate 3D objects as one path?

Under IMPORT SHAPES → 3D IMPORT the built-in TRIO and BLOCKS shapes are arrangements of genuinely separate objects. The tracer works out a single continuous route that visits all of them, which is exactly the "beam takes turns" answer applied to geometry.

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Three separate objects. One beam. One continuous path that visits all three, every redraw.

Turning the arrangement is what makes the single path believable. The three spheres swing around each other as one piece, because there was never more than one signal describing them:

Three objects on screen, one continuous route through all of them, redrawn from scratch every pass.

Turn HIDE HIDDEN LINES on and off while you watch it — with it on, the objects read as solid and one passes behind another; with it off you get the see-through tangle. It also frees up a large share of the points you were spending on edges nobody could see. The full walkthrough is in converting a 3D model to oscilloscope or laser art.

What does the MIXER do if it cannot make two objects?

The MIXER in Performance mode stacks several shape sources into one output, and it is the fastest way to watch summing fail on purpose. Its ADD blend mode is the classic sum — the one that produced the four-lobed figure above. The other blend modes (MULT, DIFF, MOD, FOLD, MIN, MAX) combine the same two sources by different rules and give you a different single path each time. None of them makes two objects, but hearing and seeing the difference between them is the fastest way to build intuition for what combination actually does. See Performance Mode for the full layer stack.

Can a laser draw two objects with the beam off in between?

Yes — this is the one place the constraint genuinely lifts. A laser projector has a blanking channel, so the beam can be switched off between objects. Under LASER OUTPUT, Auto-blanking inserts those beam-off moves for you, and Jump threshold sets how large a jump has to be before it counts as travel rather than drawing. Separate objects, no connecting lines. Details in Hardware.

How do you tell which of the four you are doing?

When a piece looks like a mess, ask which of these you are doing:

• Summing — you get one new object. Good for texture, useless for composition.
• Switching slowly — you get flicker.
• Switching fast — you get several objects and softer corners.
• Cutting the phase — you get several objects, keep the sharpness, and the arrangement stays tied to the music.

Almost every "how did they do that" moment in oscilloscope music is the fourth one.

What should you read next?

New to all of this? The oscilloscope music guide starts at the beginning: why a stereo signal draws a picture at all, and what makes an image sit still instead of drifting. If your corners look soft once you have several objects on screen, that is the other constraint doing its work — why your oscilloscope image is blurry explains the sample-rate side of the same budget.

Two subjects, one beam. beamtracer.com — I'll see you in the next one.