dopplereffect
NO CAMERA. JUST SOUND WAVES.
INTERACT WITH SOUND WAVES

Put your movement into sound.

No need to touch the screen. Move your hand and make invisible waves visible.

Experimental laboratory 01
Motion fieldReady to begin
− Δf
+ Δf
+

It starts with a movement.

Open the sound field and move your hand toward your device.

f₀ ± Δf
Moving closerSOUND FIELD / STANDBY Moving away
Movement direction
Waiting↔

Your movement will appear here.

Frequency shift Δf
—Hz

Change in the reflected sound's frequency

Carrier signal
—dB SNR

Measured for your device at startup.

Sound traceFrequencies around the carrier
Waiting for a measurementAutomatic frequency
The waves will appear here when the sound field opens.
−300 Hz · AwayCarrierCloser · +300 Hz
Experiment settingsFine-tune for your device
Balanced

Higher sensitivity may also detect movement around you.

Changes apply the next time you start.

8%

If you hear the tone or find it uncomfortable, lower the level or stop.

↗Now set a world in motion.Echo Islands · A platform adventure with the same hand controls.Play the game

This is an acoustic motion experiment. Detection depends on your device, surroundings, and hand position.

PREPARING THE SOUND FIELD

First, allow microphone access.

After permission, you will have 5 seconds to position your hand.

Waiting for microphone permission…

Keep media volume at 100%.
THE PHYSICS BEHIND THE EXPERIMENT

An invisible sound.
A measurable movement.

Your device emits a tone between 18 and 20 kHz. As your hand moves, it reflects some of that sound; the microphone looks for a change in its frequency. This is called the Doppler effect .

↗

Move closer

The reflection's frequency rises.
The sound field compresses.

↙

Move away

The reflection's frequency falls.
The sound field expands.

For a good first try

Use the built-in speaker and microphone, and keep your device still. Start with your hand 10–40 cm away, moving toward the speaker and microphone. This distance is guidance, not a measured or guaranteed range. Try one hand in a quiet space.

What can it detect?

It detects movement toward and away from the device. A stationary hand's location, distance, finger shape, or sideways movement cannot be reliably determined. Other moving objects may also trigger a response.

Air tap and double tap

Give a short push toward the device and immediately pull back. One brief forward-and-back cycle is interpreted as a tap; two consecutive cycles make a double tap. This gesture sequence is experimental: it does not measure physical contact or finger shape. In Echo Islands, one tap jumps straight ahead. A second tap during the jump adds 2 lights when you land on the same island.

Does my device support it?

You need a current browser, HTTPS, a speaker, and microphone permission. Some phones and sound cards filter high frequencies; calibration checks for this. If no signal is found, set media volume to 100%, disconnect headphones and Bluetooth, and retry with automatic frequency. On iPhone, turn off silent mode and open the page in Safari.

Sound and privacy

Some people may hear the high-frequency tone. Media volume should be at 100%; the app separately limits the signal level. Stop if it is uncomfortable. Microphone audio is processed live only on your device. It is never recorded or sent to a server. The experiment stops when the tab goes into the background.

Scientific basis: SoundWave · Microsoft Research, CHI 2012 ↗
Browser support: MDN · Microphone access ↗
FIRST STEP · PREPARE THE SOUND

Turn media volume
all the way up.

Use your device's volume buttons to set media volume to 100%. Disconnect headphones and Bluetooth so sound plays through your device's speaker.

The sound is usually inaudible because of its high frequency; there is no need to worry about setting the volume to 100%.

Then place your device on a stable surface. After microphone permission, a 5-second countdown lets you move your hand away and hold it still. Keep that position once measurement begins.