The Doppler effect is a well-documented phenomenon in physics which causes a change in the frequency of a wave as the source moves closer to the observer. It's the science behind satellites and speed cameras alike. And, in the hands of one computer science student, it can make a little magic happen on your computer.

The idea of using the Doppler effect to interact with a computer, using just a microphone and speakers, was first explored by a Microsoft research team in 2012. The technique is reasonably simple: an inaudible, high-frequency tone is emitted by your speakers. When the soundwave reflects off moving object (read: your hand), it's frequency-shifted, a shift which is measured using the microphone, and interpreted as a gesture by the computer.

The team successfully recognised a wide range of gestures — scrolling, taps, pinches and rotation — but the project was never really seen as anything more than a "supporting act" for Microsoft's Kinect sensor.


This is where Daniel Rapp, a Swedish computer science student, comes in. Having read the Microsoft research paper he set out to replicate the results, and ended up building this webpage with a bunch of Doppler demos embedded.


As long as you have a working microphone and speakers in your laptop (and you're running Chrome), you can scroll up and down the page, play a Theremin, or just watch the computer track you waving your hands around like an excitable Harry Potter extra.

The demo is a neat proof of concept, even if it's not a genuinely useful project in and of itself. But given the number of devices packing microphones and speakers, this technique could be used to add gesture control into almost anything. Now, whether or not you'd prefer to scroll with your whole hand, or just your middle finger, is a completely different story. [Daniel Rapp/Github]