microtonal scale builder — for OP–1 field, OP-1, OP-Z

Explore microtonal & non‑octave tunings on the Teenage Engineering OP–1 field.

Load a Scala .scl file, pick a waveform, and the tool synthesises one short, seamlessly‑looping tone per scale degree and bakes them into an OP‑1 field drum patch (.aif). Each key of the drum kit plays an exact microtonal pitch, sustained for as long as you hold it.

It's a single self‑contained HTML file — no build step, no dependencies, nothing leaves your browser. Just open it.

ℹ️ The microtonality lives in the rendered audio (each slot is rendered at its true frequency with the patch's pitch field left at 0), which sidesteps the OP‑1's semitone‑quantized pitch control and gives exact tuning — measured under 0.1 cents of error across all keys.

---

quick start

1. Open microtonal-op1f-builder.html in a desktop browser (Chrome, Edge, Safari or Firefox).
2. Pick a built‑in preset, drop in a .scl file, or load a whole folder of .scl files.
3. Set the root frequency, root key, waveform and level.
4. Audition with your computer keyboard (see below).
5. Click export .aif and drop the file onto your OP‑1 field as a drum patch.

No server needed — file:// works. If you prefer one:

python3 -m http.server 8000
# then visit http://localhost:8000/microtonal-op1f-builder.html

---

loading a scale

The Scala .scl format is supported in full (cents and ratios, arbitrary periods):

• Preset dropdown — 12‑TET, just‑intonation major (Ptolemy), 19‑TET, Bohlen–Pierce.
• Single file — drag‑and‑drop or click to load one .scl.
• Folder — load .scl folder reads every .scl in a directory (and its sub‑folders) and lists them in a dropdown, so you can flip through a whole tuning library. Files are read locally; nothing is uploaded.
• Paste / edit — paste raw Scala text and hit parse text.

The parser handles comment lines (!), the description line, the note count, and pitch lines as either cents (700.0) or ratios (3/2). The implicit 1/1 is added automatically and the last entry is treated as the period (an octave 2/1, a tritave 3/1, or anything else).

---

controls

control	what it does
root freq	Frequency (Hz) assigned to the root key. Shows the nearest note name.
root key	Which of the 24 drum keys the root sits on. The scale extends up and down from there, repeating every period.
tone length	Length of each rendered loop (0.05–0.5 s). Shorter = more headroom in the 12 s buffer.
level	Per‑note peak level in dBFS (default −14 dB) so stacked/polyphonic notes don't clip.
waveform	sine · triangle · sawtooth · square · FM (2‑op) (ratio + depth) · custom additive (8 harmonic faders).

The 24‑key grid live‑updates, showing each key's scale degree, cents, and exact frequency, with the root key highlighted. Click any key to audition it.

---

playing on the computer keyboard

Audition the tuning before exporting:

 a  w  s  e  d  r  f  g  z  h  u  j  i  k  l  p  é      ← ascending scale steps (a = root)
 y / x                                                  ← octave down / up

• Fully polyphonic with seamless looped sustain while held.
• Keys are matched by physical position, so the same physical keys work on any keyboard layout (the labels above are Swiss QWERTZ).
• Browsers require a gesture before audio — click the page once if it's silent.

The computer keyboard is for monitoring only; it doesn't change the exported file.

---

using the export on the OP–1 field

1. Connect the OP‑1 field over USB and enter content / disk mode.
2. Copy the exported .aif into a drum preset folder (e.g. /drum/).
3. Select it in drum mode. Holding a key now sustains the corresponding microtonal pitch.

The exported patch is a standard OP‑1 drum kit, so per‑key tweaks on the device (volume, etc.) still work from there.

---

how it works

The output is a .aif exactly as the OP‑1 expects:

• 44.1 kHz · 16‑bit · mono · 12 s AIFF, with the proprietary op-1 JSON metadata embedded in an APPL chunk.
• The 24 tones are concatenated into the buffer; each slot's start/end mark its region, normalised over the buffer the way the OP‑1 stores sample positions.
• playmode is set to 28672 (loop) for every slot, so holding a key loops between start and end → sustained tone.
• pitch is 0 for every slot (tuning is in the audio, not the pitch field).

Seamless loops: each tone is rendered as an exact integer number of waveform cycles. The fundamental is nudged by a fraction of a cycle so a whole number fit the slot length, which makes the start → end loop click‑free. FM ratios and additive harmonics stay periodic at the fundamental, so they loop cleanly too. Measured tuning error stays < 0.1 cents.

---

compatibility & notes

• Built and tested against the OP‑1 field drum patch format; should also load on the original OP‑1 and OP‑Z (same drum‑patch format).
• Output is mono. The OP‑1 field's stereo drum engine plays mono samples fine.
• The drum loop play‑mode value (28672) is community‑reverse‑engineered, not officially documented — verified against real patches and existing tooling. If a loop seam is ever audible, raise the tone length slightly.
• The folder picker needs a Chromium‑based browser, Safari, or Firefox on desktop.

---

acknowledgements

• The Scala scale file format by Manuel Op de Coul.
• OP‑1 drum‑patch format details cross‑checked against schollz/teoperator and brian3kb/digichain.
• OP‑1 / OP‑1 field are products of Teenage Engineering. This project is unaffiliated and not endorsed by them.

---

license

MIT — see below. (Swap this out if you prefer something else.)

MIT License

Copyright (c) 2026

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated files, to deal in the software without
restriction, including the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies, subject to the following:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND.