What makes 17edo special is that it has two distinct personalities living inside the same tuning system...
What makes 17edo special is that it has two distinct personalities living inside the same tuning system. The first is familiar: a sharp, dramatic version of the diatonic scales and circle-of-fifths harmony you already know, with all your keys and chord functions intact, just requiring careful use of timbre. The second is something genuinely foreign: a set of neutral scales built from stacked neutral thirds, saturated with Middle-Eastern color, and governed by a completely different harmonic logic rooted in the 13th harmonic rather than the familiar major third. You can spend years in either world, or write music that moves between them.
Don’t let the “microtonal” label scare you off. If you understand major scales, circle of fifths, and what a minor third sounds like, you have everything you need to follow along.
What Is 17edo?
17edo (short for “17 equal divisions of the octave”) simply means we slice the octave into 17 equal pieces instead of 12. Each step is about 70.6 cents wide, compared to the 100-cent steps of 12edo. That’s a noticeably smaller step — about 29 cents narrower — which gives the system a very different melodic character.
Each step in 17edo represents a frequency ratio of the 17th root of 2. In practical terms: the scale has 17 notes before you arrive back at the octave, and all 17 are equally spaced.
The idea is older than you might think. In the thirteenth century, Middle-Eastern musician Safi al-Din Urmawi developed a theoretical system of seventeen tones to describe Arabic and Persian music, although the tones were not equally spaced. This 17-tone system remained the primary theoretical system until the development of the quarter tone scale. SevenString So 17 notes per octave has a long history in theory, even if equal-tempered 17edo is a more modern formulation.
It Still Has a Diatonic Scale
Here’s the key thing that makes 17edo so approachable for conventionally trained musicians: it still has a recognizable diatonic scale. Your C major scale still exists. You still have a circle of fifths. Chord progressions like I–IV–V–I still function. The familiar architecture of Western music is intact.
The reason is that 17edo has a perfect fifth of about 705.9 cents — only about 4 cents sharper than the 702-cent just perfect fifth, and about 6 cents sharper than 12edo’s 700-cent fifth. That’s a small enough difference that your ear still hears it as a fifth. Stack those fifths around a circle and you get all the notes and key relationships you already know.
The diatonic major scale in 17edo has the step pattern 3 3 1 3 3 3 1 (in scale steps), compared to 12edo’s 2 2 1 2 2 2 1. The half steps are much smaller (just one step, or ~71 cents) and the whole steps are notably wider (three steps, or ~212 cents). This creates a harder, more dramatic contrast between the tones and semitones of the scale — like Pythagorean tuning cranked up a notch. Melodies feel more angular and decisive; leading tones have a stronger pull toward resolution.
The Weird Part: Sharps Are Higher Than Flats
This is where things diverge from what you’re used to, and it’s important to understand.
In 12edo, C# and Db are the same pitch. They’re enharmonically equivalent. In 17edo, they are not — and C# is actually higher than Db. Each flat and each sharp spans two scale steps (about 141 cents), while the diatonic semitone (like E to F) is only one step (~71 cents). So a sharp is twice as large as a minor second. This is the opposite of meantone tunings like 19edo, where flats are higher than sharps.
The result is a chromatic scale that looks like this:
C — Db — C# — D — Eb — D# — E — F — Gb — F# — G — Ab — G# — A — Bb — A# — B — C
Seventeen notes, with each sharp sitting one step above its enharmonic flat neighbor. If you’ve ever read about Pythagorean tuning behaving this way, you’re on the right track — 17edo is essentially a closed, equal-tempered version of that Pythagorean logic. The SeventeenTheory page on the Xenharmonic Wiki has great diagrams showing the circle-of-fifths structure if you want to explore this further.
Where 17edo Shines and Where It Struggles
17edo has a strongly opinionated relationship with the harmonic series. Here’s what you need to know:
The 3rd harmonic (perfect fifths and fourths) is excellent — barely 4 cents off from pure. This is why the diatonic system still works so well.
The 7th harmonic is quite good, with an error of about +19 cents. Intervals related to the number 7 — like the septimal minor third (7/6) or the harmonic seventh (7/4) — are reasonably well represented.
The 11th and 13th harmonics are also approximated with modest errors, opening up a range of unusual but coherent neutral and exotic interval colors. As we’ll see below, the 13th harmonic in particular gives 17edo one of its most distinctive and beautiful features.
The 5th harmonic, however, is a disaster. The major third in 17edo lands at about 353 cents — more than 33 cents flat of the 386-cent just major third (5/4), and actually much closer to an 11/9 neutral third or a 16/13 tridecimal neutral third. If you try to play a standard major triad in 17edo, it will sound jarringly dissonant. The major third just doesn’t function the way you expect. This is probably the single biggest adjustment for conventionally trained musicians.
So What Do Chords Sound Like?
If major triads are out, what replaces them? This is where 17edo gets genuinely exciting.
The system naturally gravitates toward chords built from the 7th, 9th, and 11th harmonics instead of the 5th. The 17edo page on the Xenharmonic Wiki describes the characteristic sonorities as including the tetrad 6:7:8:9, which in 17edo is voiced as steps 0–4–7–10. This chord has a rootsy, slightly Middle-Eastern quality — grounded but with a different kind of warmth than a major triad.
The “mid third” or neutral third — 5 steps, about 353 cents — lands between a minor and major third. It approximates intervals like 11/9 and 16/13. Chords built with it have an ambiguous, floating character that doesn’t quite read as major or minor, and can be incredibly evocative.
The minor third, at 4 steps (~282 cents), is actually closer to the septimal minor third 7/6 than to the classical minor third 6/5. It sounds noticeably narrower and more compressed than the minor third you’re used to.
All of this means that while your 12edo harmonic vocabulary doesn’t directly transfer, a new one opens up — one that leans into these 7-, 11-, and 13-limit colors.
Going Beyond the Diatonic: The 17edo Neutral Scale
Here’s something that often surprises musicians when they first encounter 17edo: diatonic music is just the beginning. One of the most beautiful modal systems available in 17edo has nothing to do with major and minor keys at all. It’s called the 17edo neutral scale, and it’s built on a completely different principle.
Instead of stacking perfect fifths to build a scale (the way the diatonic system works), the neutral scale is built by stacking neutral thirds. Specifically, you repeatedly add an interval of 5 steps (353 cents) upward and downward from a starting pitch. When you’ve stacked enough of them to generate 7 distinct notes, you arrive at a scale with the step pattern 2 3 2 3 2 3 2 — alternating smaller steps (~141 cents, a neutral second) and larger steps (~212 cents, a major whole tone).
Written out in cents from the root, this 7-note neutral scale looks like:
0–141–353–494–706–847–1059 — (1200)
Notice what’s in there: a perfect fourth (494 cents), a perfect fifth (706 cents), and a familiar octave. Those pillars of tonal stability are still present, giving the scale a coherent structure even as everything in between sounds completely unfamiliar. The neutral seconds and thirds create an instantly recognizable Middle-Eastern or maqam-like flavor.
One of the most striking harmonic features of this scale is the neutral sixth, which falls at 847 cents. This interval comes very close to the 13th harmonic — the just ratio 13/8, which is 841 cents. Its inversion, the neutral third at 353 cents, correspondingly approximates 16/13. This means the neutral scale is, at its core, a 13-limit harmonic system — a mode of expression built on the relationship between the 3rd and 13th harmonics rather than the familiar 4:5:6 of Western harmony.
The scale has seven modes, just like the major scale has seven modes (Dorian, Phrygian, etc.). Each starts on a different degree. Some of them lean closer to major-scale territory; others are more exotic. Because of the alternating step pattern, these modes all share a characteristic shimmering quality — the narrow neutral seconds give melodies a gliding, Arabic or Persian feel, while the regular presence of fourths and fifths keeps everything grounded.
Crucially, this scale deliberately locks you out of 12edo habits. As the Xenharmonic Wiki notes, the 7-note neutral scale contains no major or minor triads whatsoever — you cannot build them from its notes. There is one minor third, but it appears only over a diminished fifth, giving you a diminished triad with no pure minor triad possible. There are no major thirds at all. This isn’t a bug — it’s the point. The neutral scale gives you a self-contained harmonic universe where the emotional vocabulary of major and minor simply doesn’t apply.
If you keep stacking neutral thirds past 7 notes, you eventually arrive at a 10-note neutral scale — a larger, richer system that begins to sound like two interlocking pentatonic scales a neutral interval apart. The 10-note version opens up chords like 8:11:13, which have a sound unlike anything in the standard Western palette. Adventurous players have noted that this scale unlocks some remarkably intense blues-inflected licks — just not blues as you’ve ever heard it.
Two Worlds in One Tuning
What makes 17edo particularly fascinating as a starting point for microtonality is that it genuinely offers two distinct musical worlds within the same tuning system:
The first world is the extended diatonic. Your circle of fifths is still there. You can write functional harmony, you can modulate between keys, you can notate everything on a standard staff. The flavor is sharp and Pythagorean — dramatically different from 12edo but immediately recognizable as coming from the same tradition. This is the world that composers like Easley Blackwood, whose Microtonal Etude №7 in 17edo is one of the definitive pieces in the tuning, explored systematically.
The second world is the neutral modal. Driven by the 13th harmonic and built from stacked neutral thirds, this is genuinely xenharmonic — not a retuning of Western harmony but a different harmonic logic entirely. It connects naturally to the maqam traditions of the Middle East, which have used neutral intervals for centuries.
Most tuning systems force you to commit to one approach or the other. 17edo offers both, and the contrast between them is itself a compositional resource.
A Note on Timbre
One practical consideration: because 17edo doesn’t approximate the 5th harmonic well, using instruments with a strong 5th partial will produce beating that can work against you. Synthesizers are ideal — you have full control over the overtone structure. Sine-wave-based or odd-harmonic-heavy timbres (like clarinets, which naturally suppress even harmonics) tend to work well. String instruments and pianos will still work, but the beating from the mistuned major thirds is part of the aesthetic, not something you can tune away.
For the neutral scale specifically, you actually want instruments with a strong 13th partial, which is unusual. In practice, many players find that lighter, cleaner timbres — plucked strings, mallet instruments, clean electric tones — bring out the floating, shimmering quality of the neutral intervals most beautifully.
Getting Started
The most common way musicians explore 17edo today is through software. Any synth that supports Scala tuning files or MTS (MIDI Tuning Standard) can be retuned to 17edo. Free tools like Scala and ODDSound MTS-ESP can retune your existing plugins in a DAW.
If you want to hear what’s possible, the 17edo music page on the Xenharmonic Wiki has an enormous list of pieces across genres — ambient, jazz, prog rock, baroque arrangements, piano solo work, and more. The artist norokusi has written dozens of piano sonatas and short pieces in 17edo that demonstrate the full range of the tuning’s chord colors. The Mercury Tree’s album Spidermilk is a full-length prog record in 17edo that’s very accessible for rock listeners. Adam Freese’s piece Sea of Pollen (2024) specifically explores the mosh/3L 4s neutral scale system described above, and is a great demonstration of what that modal world actually sounds like in practice.
The Seventeen-Tone Piano Project was an academic initiative that resulted in numerous composed pieces and concerts in 17edo and is worth exploring for sheet music and compositional approaches.
The Bottom Line
17edo is not just “12edo with extra notes.” It’s a tuning system with two distinct personalities. In its diatonic mode, it takes the perfect fifth seriously — building a sharp, angular, Pythagorean-flavored version of the music theory you already know. In its neutral modal mode, it draws on the 13th harmonic to open up a completely different world: shimmering Middle-Eastern scales with no major or minor triads, built from stacked neutral thirds and saturated with an interval color that has no name in Western tradition.
For musicians with a solid grounding in conventional theory, 17edo is one of the most navigable entry points into microtonality — because the diatonic skeleton is still there when you need it. But the neutral scale gives you a genuine escape hatch: a coherent, beautiful system that sounds nothing like anything you’ve played before, using the same 17 notes.
You’re not starting from scratch. You’re learning that the house you already live in has a door you never noticed — and on the other side is something genuinely new.
Further reading: 17edo on the Xenharmonic Wiki | 17edo Neutral Scale | SeventeenTheory | 17edo Music | Seventeen-Tone Piano Project
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