What Is Microtonal Music and How Do You Compose With Microtonal Scales?

Microtonal music is music that uses pitches outside the twelve equal semitones of standard Western tuning — for example quarter tones, just intonation, or historical and experimental temperaments. You compose with it by choosing a tuning system, mapping it to your instruments, and editing note pitches at a finer resolution than a piano roll normally allows. Helio, an open-source sequencer for desktop and mobile, is explicitly built to encourage experimentation in "exotic scales and microtonal temperaments," so it works as a concrete example of how this looks in practice.

What makes music "microtonal"

Standard Western tuning divides the octave into 12 equal steps (12-tone equal temperament, or 12-TET). Each step is 100 cents, and an octave is 1200 cents. Microtonal music uses intervals that don't land on those 100-cent grid points.

That covers a wide range of systems:

Quarter tones — 24 equal steps per octave, 50 cents each. Common in modern classical and some Middle Eastern traditions.
Just intonation — intervals built from simple frequency ratios (3:2 for a perfect fifth, 5:4 for a major third) rather than equal steps. Chords sound beatless in one key but drift in others.
Other equal divisions — 19-TET, 31-TET, 53-TET, and so on, each trading off how well different intervals approximate just ratios.
Historical and regional temperaments — meantone, Pythagorean, and various maqam and raga systems that predate or sit outside 12-TET.

The practical difference: in 12-TET a major third is 400 cents. In just intonation it's about 386 cents. That 14-cent gap is small but audible as a change in how "locked in" a chord sounds.

Why composers use it

Three recurring motivations:

Harmonic accuracy. Just intervals have no beating, so sustained chords can sound cleaner than their equal-tempered equivalents.
Expressive color. Quarter tones and other inflections add melodic tension that 12-TET can't produce.
Cultural and historical fidelity. Music written for non-Western or pre-20th-century tuning systems is often approximated poorly by 12-TET.

How a sequencer handles microtonal scales

A conventional piano roll assumes 12 notes per octave. A microtonal-capable sequencer has to do more than that. Helio's stated design goal is to "encourage experimentation in underexplored areas in music, like exotic scales and microtonal temperaments," which means the scale and tuning layer is part of the composition workflow rather than an afterthought.

In practice, the pieces you need to control are:

The scale or temperament — which pitches exist and how they're spaced.
The note grid — how finely you can place and edit pitches.
The instrument's tuning — whether the sound source actually plays the pitch you specified.

The third point is where most microtonal work breaks, so it's worth treating separately.

Practical steps for composing microtonally

The exact menus differ by tool, but the sequence is consistent:

Pick a tuning system. Decide on a specific equal division, a just-intonation set, or a custom scale file. Vague intentions ("I want it to sound exotic") don't translate into editable pitches.
Set the scale in the sequencer. Load or define the temperament so the note grid reflects your chosen pitches rather than 12-TET.
Choose instruments that accept pitch data. This is the critical step — see the pitfalls below.
Edit notes at the required resolution. If your scale has 24 or 31 steps per octave, you need note placement and pitch-bend resolution to match. Coarse grids will quantize away the intervals you're trying to use.
Verify by ear and by measurement. Play a sustained interval and listen for beating. If a just fifth beats, something in the chain is retuning it.

Expected result: notes land on the intended cents values, and sustained intervals sound as the chosen system predicts.

Common pitfalls

Instruments that ignore your tuning

Most sample-based and many synth VSTs are hardwired to 12-TET. They receive a MIDI note number and play a fixed pitch. If your sequencer sends a microtonal pitch as a note number, the instrument snaps it to the nearest semitone.

Workarounds:

Use synths that support MIDI tuning standards or Scala (.scl) / tuning-table files.
Send pitch as pitch-bend data per note, which most synths do respond to — but check the bend range, since a default of ±2 semitones may not cover your intervals.
Use MTS-ESP-style dynamic tuning, if your host and plugins support it.

Pitch-bend range mismatches

If the sequencer assumes a ±2 semitone bend range and the synth is set to ±12, every microtonal note plays at the wrong offset. Match the ranges explicitly.

Quantization erasing your intervals

A grid set to 1/16 notes is fine for rhythm but says nothing about pitch. Make sure pitch editing isn't snapping to 100-cent steps.

Chords that only work in one key

Just intonation is key-dependent. A chord that's beatless in C may sound rough after a modulation. Decide whether you want a fixed just tuning, a adaptive one, or an equal division that compromises across keys.

Choosing a tool

If you want to explore microtonality, the deciding factors are:

Does the sequencer expose scale/temperament settings directly? Helio lists exotic scales and microtonal temperaments as a design focus, which puts it in the "built for this" category rather than "possible with workarounds."
Does it run where you work? Helio ships stable builds for macOS, Windows (installer and portable 32/64-bit), Linux (AppImage, deb, tarball), iOS, and Android, plus development builds for the same platforms.
Can your instruments follow? No sequencer can fix a plugin that ignores tuning data. Budget time for testing your sound sources.

Helio is open-source and its documentation covers hotkeys, refactoring options, and arpeggiators — useful once the tuning layer is set up, since microtonal parts often need more editing passes than 12-TET ones.

Where to start

Pick one system — quarter tones are the gentlest entry point — set it up in your sequencer, and write a short piece using only that scale. The goal of the first attempt isn't a finished track; it's confirming that the pitches you specify are the pitches you hear. Once that chain is verified, the compositional questions (which intervals, which chords, which keys) become the interesting part.