Unheard

There's a plane you can't hear.

Hold your phone up to the sky for a couple of minutes. Unheard finds the faint drone hiding in the background noise and tells you which plane made it.

Your recording stays on your phone unless you choose to give it.

How it works

  1. 01

    The Doppler curve

    A propeller hums at a steady pitch. While the plane comes toward you the pitch is a little higher, once it leaves a little lower. That bend is usually too faint to hear, but it is there in the sound, and a spectrum shows it.

  2. 02

    The flight data

    Most aircraft broadcast their position, speed and altitude every second. While you listen, the page follows every one of them within 30 km, using only your rough area.

  3. 03

    The match

    For each aircraft, your phone works out the exact curve you should have heard where you stand, including the seconds the sound took to reach you, and looks for it in your recording. The one that fits is the plane you heard.