Polyphony tricks — how to simulate chords on a quadcopter

A standard quad has four monophonic voices — one per motor. A standard chord has three or four notes. So mathematically you've got just enough motor lanes to play full chords if you're careful, but a lot to lose if you're not.

Here's what I've learned from arranging chord-heavy songs for ESCs.

The pitch range problem

Your motors play roughly C4 to B7. That's four octaves — wide enough for most things. But chords sound best when their notes span no more than two octaves; spread them wider and your ear stops hearing them as a single chord and starts hearing them as overlapping melodies.

Practical rule: keep all chord tones within an octave and a half of each other. Use Octave shift on the converter to bring outliers in.

Voice leading matters more than chord substance

If you just have your converter route random chord notes to random motors, you'll get jumpy, ugly transitions between chords. Each motor independently jumps up or down by a fifth or octave between chord changes, and your ear hears it as chaos.

Voice leading is the trick: each motor should move as little as possible between chords. If motor 1 plays C in chord 1 and the next chord is G major, motor 1 should play G or B — not E.

The converter's track-to-motor affinity helps with this when your MIDI is well-arranged. If your MIDI uses dedicated voice tracks (soprano / alto / tenor / bass), affinity will keep each one on its own motor and voice leading happens automatically.

If your MIDI is just one stacked chord track, the allocator will jumble it. Either re-arrange the MIDI into separate tracks per voice before converting (a few minutes' work in any DAW), or accept the jumble.

Triads work better than seventh chords

Major and minor triads (3 notes) sound clean on motors. Seventh chords (4 notes) sound muddy because the seventh interval clashes with the harmonics that your motor naturally puts out.

If your song uses seventh chords, consider dropping the seventh. The chord progression survives; the cluttery overtones don't.

Chord types that sound great

• Open fifths (root + fifth). Two voices, easy to hear, sound modal and powerful. Lots of metal and Celtic music uses these.
• Major triads in close position. Three voices. Classic, bright.
• Minor triads in close position. Three voices. Classic, sad.
• Sus2 / sus4 (root + 2nd or 4th + fifth). Three voices. Sound modern and unresolved.

Chord types to avoid

• Diminished sevenths. Too dissonant on square waves. Sound metallic and ugly.
• Anything with very close intervals (semitone clusters). The square-wave harmonics fight each other and you get beating.
• Dense extended chords (9, 11, 13). They sounded big on a piano. They sound like a stuck horn on motors.

A worked example: Pachelbel's Canon

Four voices in the Canon are perfect for a quad. The chord progression is D - A - Bm - F#m - G - D - G - A, repeated. Each chord is a triad (three notes) plus the bass line walking underneath. Eight chords, four voices.

We arranged this for a 4-motor build. Each motor got one voice — soprano on motor 1, alto on motor 2, tenor on motor 3, bass on motor 4. The chord progression came through clean. Voice leading is so smooth in the original that affinity took care of it without manual pinning.

The result sounded like a tiny brass quartet. Not great brass, but unmistakably four voices working together rather than four motors honking randomly.

Try it yourself

Pick a song you like. In your DAW, split each chord into separate voices (top voice = soprano, bottom voice = bass, etc.) and save each as a separate track in the MIDI. Then convert. You'll be amazed how much better four-part-voiced motor music sounds compared to chord-block voicing.

The converter does the hard scheduling work — your job is just to give it well-arranged voices to schedule.