iOS App Acoustically Measures Distances Up To 25 Meters

[wraggster]

A recently published app for the iOS platform (http://iqtainment.wordpress.com/acoustic-ruler/) uses the propagation of sound waves to measure distances of up to 25 meters in a dual device mode. The technique works through repeatedly sending a chirp signal from the master device to which the other (reflector) device synchronizes itself and then replies in a similar fashion. A novel combination of techniques has been engineered to enhance the robustness in noisy environments, such as using an optimum-autocorrelation-signal and semi-automatic frequency calibration together with an averaging over multiple cycles."

http://apple.slashdot.org/story/11/11/13/1841204/ios-app-acoustically-measures-distances-up-to-25-meters