LAB-02 · doppler
Sonar Array
Your laptop is a bat. It sends out a silent 19 kHz tone and listens for the echo off your hand — the pitch shifts up as you approach, down as you pull away. Move your hand near the screen and watch the scope. Audio never leaves your device.
motion
— still —
doppler shift
calibration drill
Wave your hand at the screen three times to lock the array.
Browser sonar — FAQ
How does browser sonar work?
Your speaker plays a steady, near-inaudible 19 kHz tone. When your hand moves, it reflects that sound back to the microphone at a slightly shifted pitch — the Doppler effect. Moving toward the mic raises the pitch; moving away lowers it. The page measures that shift and shows the motion on a scope.
Why do I need to allow the microphone?
Sonar needs to listen to its own reflected tone to detect motion. The audio is analysed entirely on your device and never leaves the browser — nothing is recorded or uploaded.
It is not detecting my hand. What is wrong?
Use a laptop or phone with the speaker and mic close together, turn the volume up a little, and move your hand 10–40 cm from the device. Very quiet volume, external speakers far from the mic, or speakers that cannot reproduce 19 kHz will all weaken the effect.
Can I hear the tone?
Most adults cannot hear 19 kHz, but many children, teenagers and some adults can — it may sound like a faint whine. Pets can often hear it too. Keep the volume moderate.