By using five microphones, a speaker, and a sophisticated new echolocation algorithm, researchers have successfully built a full 3D image of a cathedral’s insanely complex interior. The same technology could someday allow humans to navigate in total darkness.

Top image: Fine Art America.

Bats, dolphins, and some visually impaired humans use reflected sound to create a mental 3D image of their environment. It’s called echolocation, and it’s a principle that was recently used by a team of researchers at the Swiss Federal Institute of Technology in Lausanne to map the interior of rooms.


In one particular experiment, the researchers set up five microphones in a Swiss cathedral. After a speaker gave off an audible chirp — sweeping from 200 hertz to 10 kilohertz — the software took over. It was able to distinguish between stronger and weaker echoes, and how many times they bounced around the room. The algorithm was strictly interested in the differing arrival times of the echoes; amplitude was not considered in the calculations.

The software compared the signals coming into each microphone. The time delays, which we humans hear as either echoes or reverb, are often incredibly small. But these infinitesimal lags are what allowed the researchers to measure the dimensions and locations of spaces —sometimes down to just a few millimeters.


The method wasn’t perfect, however. The software couldn’t map the arched roof of the cathedral.

Looking ahead, this technique could be integrated into a mobile phone or a Google Glass-like device. But to do so, the researchers will have to find a way to perform the same task with just one or two microphones set at relatively close distances to each other. Alternately, they could use multiple mobile devices cooperating over Bluetooth or WiFi.


Using this technology with a Glass-like device would be particularly helpful. The wearer could walk into a dark room and suddenly have a rudimentary map of the environment show up in their head’s up display.

Read the entire study at PNAS: “Acoustic echoes reveal room shape.”


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