Write acid lines worth keeping.
303 Patterns is a home for your TD-3-MO basslines. Sketch 16-step patterns in the browser, hear them on a built-in 303-style synth, and print clean pattern sheets to dial into the hardware.
Free forever, kept alive by kindness — not a trial, not a freemium tease. Your patterns stay yours — no ads, no tracking, never sold.
Program steps the way the hardware thinks
Sixteen steps of notes, octaves, accents, slides and gates — note, tie or rest, exactly like the box. Everything saves automatically as you click.
Every knob on the TD-3-MO panel
Cut off, resonance, env mod, decay and accent — plus the full Modded Out section, from soft attack to overdrive. Drag a knob on screen, then match it on the panel.
Organize patterns into tracks
Group patterns into tracks with a BPM and running order, split them across A and B sections, duplicate the good ones and reorder as the arrangement takes shape.
Send patterns straight to the TD-3
Plug a TD-3 or TD-3-MO in over USB and move sequences both ways — push a pattern (or a whole track) to its slot on the box, or read slots back off the hardware into a track. Only the 16-step sequence transfers, so there's no re-typing patterns by hand. No Web MIDI? A .syx download does the same on Safari and iOS.
Take a cheat sheet to the hardware
Print a clean pattern sheet — one pattern per page with every knob position and the full 16-step grid. Prop it up next to the TD-3-MO and dial the line straight in, no screen needed.
Everything between the idea and the hardware
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Hear it before you dial it in
Preview patterns in the browser via Open303 — close to the hardware, not exact — with drum loops to jam over.
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Acid randomizer
Stuck for a line? Generate one in any key, scale and density, audition the draft, and apply it when it rolls.
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The full Devil Fish panel
Not just a stock 303 — the whole Modded Out section too: soft attack, slide time, filter FM, overdrive, sub oscillator and more.
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Autosave everywhere
Steps, knobs and settings save as you go. Close the tab mid-tweak; the pattern is exactly where you left it.
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Light and dark
Follows your system theme — bright at the desk, easy on the eyes in a dim studio at 2am.
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Private by default
Track names, descriptions and your account details are encrypted at rest. Your secret weapons stay secret.
Stay smiling.
Free forever — no catch, no trial. Get your first pattern down in a couple of minutes.
If you can't afford it, no bother.
303 Patterns is free, full stop — no locked features, no trial. Someone else is paying so we can all keep tracks and have fun. If you'd like to be that someone, chip in what you can.
* Term borrowed from The Blindboy Podcast — credit where it's due.