HarmSyn allows harmonic synthesis to be demonstrated in real-time. It operates over the full range of human hearing (20 Hz to 20 kHz) and offers 16 harmonic sliders with which sounds can be synthesized. A set of buttons allows various waveforms to be created including sine, square, sawtooth, and amplitudes ramping up as well as down. Tremolo and vibrato can be switched on and their rates and extents adjusted. HarmSyn is primarily designed for demonstrating harmonic synthesis, but as it turns your iPad into a versatile oscillator, it can be used to test electronic equipment and to explore human hearing.