New Technology Maps a Room Using Only Microphones

microphone placed inside the Lausanne Cathedral (Credit: EPFL)
Researchers from Switzerland developed a new algorithm which can precisely measure the dimensions of a room using just a few microphones and a snap of your fingers. Indoor GPS and many other applications are on the horizon.
Researchers from the Audiovisual Communications Laboratory in the Swiss Federal Institutes of Technology (EPFL) developed a computer algorithm that can use the sound coming from four microphones to create a visual map of a room. Ivan Dokmanić  who worked on the project remarked that: "Our software can build a 3D map of a simple, convex room with a precision of a few millimeters".
The concept is not entirely new. In the animal kingdom both bats and dolphins use the same echolocation technique for navigating around and find their way as well as prey. Interestingly, the new algorithm does not require the microphones to be located in the room very precisely. According to Dokmanić "The algorithm then compares the signal from each microphone. The infinitesimal lags that appear in the signals are used to calculate not only the distance between the microphones, but also the distance from each microphone to the walls and the sound source".
The researchers claim that the ability of the new algorithm to "sort out" the various echoes picked up by the microphones is revolutionary. The algorithm analyzes each echo using "Euclidean distance matrices" and can then determine whether the echo is rebounding for the first or second time as well as create a unique "signature" of each of the walls.
The team preformed several tests to determine the accuracy of the algorithm. they began by trying it in an empty room in which they changed the position of a movable wall. and then they moved to a much more complex environment – an alcove in the Lausanne Cathedral. The first test was successful with a high degree of accuracy and the second (and much more complex test) gave good partial results. The team believes that tests using more microphones will very likely to yield improved results.

There can be many potential applications. Besides helping to create 3D models of buildings for architectural prepuces, the team suggested that using the technology in mobile devices can help develop "GPS-like" maps of structures from the inside. It might also be possible to design concert halls or auditoriums based upon the specific acoustics they would like to create and this is just a few examples.

More information can be found on the EPFL website.