ARCO

A two-thumb instrument. Real strings, no samples.

Left thumb sweeps a fan of scale degrees — angle picks the degree, reaching further out jumps an octave, and small wiggles bend the pitch.
Right thumb is the picking or bowing hand. Sweep across the four strings to strum; in Bow mode the sound only lives while your thumb keeps moving.
Tilt shapes tone and bend. It never picks notes — thumbs are precise, tilt is not.

Because the fan is degrees and not note names, a melody learned once plays in every key with the same motion. No headphones needed, but they help.

On a desktop: A W S E D F T G Y H U J are the degrees, Z/X change octave, space strums, 1–4 pick one string.

Setup

Thumb reach

Register

3

String order

Tilt

Practice

Screen

What each hand does

The four strings are a voicing of whatever degree the left thumb is holding, stacked bass to treble: root, third, fifth, and the degree itself an octave up. The innermost lane — where a relaxed thumb sits — is that top voice, so brushing one lane plays a melody and sweeping outward fills in the chord. 7th swaps the fifth for the seventh. Latch freezes the chord under the lower three strings and lets the melody string keep following your left thumb, which is how you accompany yourself.

Tap the back of the phone while tilt is on and the body gets struck, like knocking on a soundboard.

⟳

Turn the phone sideways

ARCO is played in landscape, one thumb per corner.

Double-tap anywhere go fullscreen and rotate