Whether it's lasers, ultrasound or radio waves, the idea is the same - someone speaking in a room creates a noise, a vibration in the air. Those vibrations move through the room towards the periphery, where they bounce off the walls and windows. Those vibrations are tiny, on the scale of a hundredth of a millimetre, but they're large enough to disturb the way that other light or sound waves bounce off the window from the other side. A spy can aim one of these devices at a window of a hotel from across the street, and piece together a reasonably good (if often very low fidelity) recording of what's happening inside the room.
Researchers at MIT, however, have managed to go one further than this - they've done it with a video camera, recording everyday objects like crisp packets and the leaves on a houseplant at high-speed. Vibrations on the scale of a five-thousandth of a pixel can be picked up after controlling for background "noise" with a suitable algorithm, giving a decent recording of the noise in the room at the time the video was made. In the announcement of the paper, due to be presented at computer graphics conference Siggraph next week, electrical engineer and lead author Abe Davis said:
When sound hits an object, it causes the object to vibrate. The motion of this vibration creates a very subtle visual signal that’s usually invisible to the naked eye. People didn’t realize that this information was there.”
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