Tunable by Affinity Blue is a new tone generator / pitch detection app that is well suited to theremin players. Just turn it on and set it in front of your theremin, and Tunable starts showing you how close you are to pitch-perfect playing. Use it in practice sessions to improve your accuracy or plug your pitch preview jack into it for help during live performances. Tunable's clear and large display is easy to see in your peripheral vision as you play.
In addition to pitch detection, Tunable can generate reference notes and chords which can be very helpful while practicing intervals on the theremin. It also features a metronome with visual flash if you don't want to hear beats over your music.
Tunable is available for just $0.99 on: iPhone, iPad, and Android.