An Arithmophone is a thing that turns numbers into sounds. Its name is derived from the ancient Greek words ἀριθμός (arithmos; number) and φωνή (phone; sound).
The new generation of Arithmophones is on iOS! The first of a new series of touchscreen musical instruments is Pentatone, available now for iPad and iPhone on the Apple App store.
Pentatone is an iOS music app featuring an expressive keyboard and a built-in synthesizer with a custom sound engine. The name Pentatone comes from the Greek words πεντᾰ (pentă; five) and τόνος (tónos; note) and the keyboard is focused on pentatonics: musical scales with 5 notes per octave. You can use it as an easy-to-play instrument, a source of melodic and harmonic inspiration or a tool for learning about music and exploring the deep connection it has with numbers.
Most iOS music apps either give you piano keys or a grid-based interface. Pentatone takes a fresh approach, optimised for the ergonomics of touchscreen devices and inspired by instruments like the kora and mbira. It also features a sophisticated scale selection system that includes all the common pentatonic scale types and unlocks some more unusual ones.
Pentatone features:
- Easy-to-play keyboard, split for two-handed playing
- Original pentatonic scale system with 9 selectable scales, in just intonation or standard tuning
- Custom AudioKit-based synth engine (binaural 2×2 operator FM with stereo detune, resonant filter, delay and reverb)
- 25 preset sounds with macro sliders for tone and ambience
- Initial touch and aftertouch response, both polyphonic
Click here to download and install Pentatone on your iPhone or iPad. For links to earlier versions of the Arithmophone (including installable web apps that also work on Windows and Android), please visit this page.
Arithmophone concept, design and development by Chiel Zwinkels © 2026