under the hood

How Etherpad sings.

There are no recordings inside Etherpad. Every note is synthesized the instant you touch the surface, by Csound — a sound-programming language trusted by composers and researchers since 1986. This is the story of how your touch becomes ether.

First, what is sound?

Four ideas explain nearly all of synthesis. Master these and the rest of this page — and most synthesizers ever built — will make sense.

Sound is moving air

Anything that vibrates pushes air in waves. How fast it vibrates is the pitch — faster means higher. How far it swings is the loudness. Everything you hear is just these two numbers, dancing.

An oscillator is a shape on repeat

Draw one tiny wave shape and replay it hundreds of times per second — like a music box cylinder spinning. The shape sets the character: sine is pure, triangle is soft, sawtooth is bright, square is hollow.

FM — waves bending waves

Frequency modulation: one wave wobbles another wave's pitch thousands of times a second. Out come shimmering metallic overtones no single wave could make — the secret behind Etherpad's bells and its signature pad.

The envelope gives it life

Real sounds are born and they die: a bell strikes then rings away, a pad blooms slowly. The envelope shapes a note's loudness over time — attack, sustain, release. It is why lifting your finger fades the note like a breath instead of cutting it dead.

From touch to tone

Your finger becomes data

The app writes each fingertip's position to named channels — touch.0.x, touch.0.y — like order tickets passed through a kitchen window. The engine reads them live, and every touch gets its own independent voice.

Movement is smoothed

Raw touch positions jump in steps that would click and zipper. A portamento opcode glides every value toward its target in a few hundredths of a second — the reason Etherpad feels liquid instead of steppy.

Position snaps to music

Your X position is mapped onto a scale table — a list of semitone steps like 0, 2, 4, 7, 9 — then snapped to the nearest step and converted to a frequency. That's why you can't play a wrong note: the grid is the key.

A voice is synthesized

The chosen sound builds the waveform live at that frequency: FM synthesis for bells and the Ether Pad, band-limited analog-style oscillators for saws and triangles, vowel filters for the choir. Y controls loudness and timbre together — higher is brighter, louder, more alive.

Meet the fourteen voices

Every sound in Etherpad is a different recipe built from the ideas above. Each has its own character — and its own way of answering your finger. The newest four were crafted by contributor Stefan Hasselmann.

Ether Pad

FM · the signature

The sound Etherpad is named for. One sine wave bends another while a slow half-second bloom fades each note in — nothing starts abruptly, everything breathes.

Distorted Dreams

filtered saw

A bright sawtooth pushed through a resonant filter that growls harder the higher your finger rides. The aggressive one.

Orelia

modal · struck steel

Hand-struck steel, tuned the way a handpan is: every tap rings on its own, the deep fundamental outlasting the shimmer the way real metal fades. Glide slowly and the steel hums under your finger.

Soft Triangle

pure wave

The gentlest voice: a single soft triangle wave, close to a flute. Nothing to hide behind — and nothing that needs hiding.

Digital Monk

vowel filter

A low drone dropped an octave and pushed through vowel shapes — slide your finger and it chants ooh… oh… ah, like a monk in a server room.

Glass Choir

formant choir

Four slightly detuned voices sing through morphing vowels — oo when you play low, ah as you rise. Airy, wide, almost human.

PWM Pad

pulse width

A square wave whose width is slowly stirred by an invisible hand — the warm, chorusing pad sound of classic 80s synthesizers.

Morphwave

wavetable

Two different waveforms, and your finger's height crossfades between them — the tone itself shape-shifts under your hand as you play.

Xanpalamin

classic FM

A vintage FM recipe with a strange name and a glassy shimmer — part electric piano, part dream.

FM Bell

inharmonic FM

Two bells cast slightly out of tune so they beat and warble like real metal, with a long ring that lingers under whatever you play next.

Nebula Drone

detuned stack · ambient

Six oscillators split across two stereo wings, each drifting slightly out of tune with its neighbors — a pad the size of a sky, made for long, slow gestures.

Crystal Rain

inharmonic FM · glass

Three FM voices tuned to golden-ratio intervals ring like struck glass. Rise higher and the shimmer quickens — every note trails a tail that sparkles for seconds.

Deep Orbit

sub drone

A sub-octave sine holds the floor while a halo of harmonics slowly rotates around it. Raise your finger and the orbit spins faster, the filter opening as it turns.

Quantum Pulse

gated pulse

The tone arrives in pulses, like a signal from deep space. Your finger's height sets the rate — low is a resting heartbeat, high is a flutter on the edge of a tone.

The signal path

Voices never reach the speakers directly. Like a recording studio, everything flows through shared mixing buses — and the effects are what make it ethereal.

Your touch — every finger a player

Voices — one per touch position → pitch → waveform → envelope

Reverba long 0.985 tail — the cathedral

Delay0.8s echoes at 70% — the canyon

Mixer soft-limit, out, clear — 1,378× a second

Music synthesis

Why it sounds ethereal

Three ingredients. A reverb with an unusually long tail keeps every note ringing after you lift your finger, like a clap in a cathedral. A feedback delay repeats each phrase softly, like a voice across a canyon — old notes linger underneath new ones. And portamento everywhere means nothing ever jumps — pitch, volume, and tone all glide. Music made of curves, not corners.

The music hiding inside

The engine is also a little music teacher. These are the ideas you're absorbing every time you play — no theory lessons required.

A scale is a recipe of steps

Music doesn't use every pitch — it walks a pattern of steps and skips, like stones across a river. Etherpad lays only those stones under your fingers, which is why you can't land on a wrong note. Pick a five-note (pentatonic) scale and every stone agrees with every other — the oldest trick in music, from Ireland to Japan.

The overtone series — nature's chord

Pluck one string and you hear one note — but hiding inside are quieter tones at exactly 2×, 3×, 4× its frequency. Notes sound good together when their hidden tones overlap. Etherpad's Overtone tunings skip the piano grid entirely and let you play this natural ladder directly — the sound of horns, bells, and throat singing.

A music box, spun faster

A music box pins one melody onto a cylinder — spin it faster and the tune rises in pitch. A digital synth does the very same thing: it stores one cycle of a wave as a little loop of numbers and replays it faster or slower. Same shape, different speed — that's the whole secret of pitch.

Ten fingers, ten voices

Each finger on the surface is its own independent singer — its own pitch, loudness, and life. They all pour into one shared mix, like a choir into a room. Hold a low drone with your thumb while a melody dances above it, and you're doing what organists and bagpipers have done for a thousand years.

Learn it, build it

The engine descends from the Csound MultiTouchXY example by Steven Yi and Victor Lazzarini, built into an instrument by Paul Batchelor. Go deeper:

Csound

The audio language powering Etherpad — free, open source.

The Csound FLOSS Manual

The best place to learn synthesis with Csound, from zero.

Note: MIDI & MPE (Beta)

Etherpad speaks MIDI and MPE, but this is still an exerimental feature, so a DAW can record every finger's pitch and tone and play it back. How faithfully that recording replays depends on the host's own MIDI engine: some hosts reproduce full per-finger expression, others simplify per-note data on playback. This is an experimental feature and keeps improving with every release — for multi-finger recording, switch MPE on.