Audio Example of Time Reversal - Speech Privacy
Various speech and music signals were selected and reversed in time. A loudspeaker and a microphone were setup in a reverberation chamber (located on the campus of Brigham Young University) with the loudspeaker and microphone pointing away from each other to make the sound field more diffuse. The reversed signals were then played from the loudspeaker and the response at the microphone was recorded. Then these signals were time reversed and rebroadcasted from the loudspeaker (original positions were maintained since reciprocity still holds). The rebroadcasted signals then focus at the microphone position and they were recorded (microphone wasn't moved). Then the microphone was moved about 2 meters away and the same signals were rebroadcasted and recorded (this time they should still focus at the original microphone location, and not where the microphone currently is).
If you listen to the recorded signals, the signals recorded at the focal position are intelligible while the signals recorded away from the focal location are not intelligible. Listen to the speech signal away from the focal location and try to guess what is being said. Then listen to the speech signal at the focal location and compare. Do the same order with the music sample. Also check out the two photos of each setup. These results demonstrate the ability of time reversal to aid in speech privacy applications.
To play the files, click on the images or links below.
For more information, contact Brian Anderson.