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Most microphones are designed to emulate the human ear, hearing sounds that we hear, and not hearing ones that we don't. Scientists from the University of Illinois at Urbana-Champaign, however, have created a new sound that we can't hear but that is picked up by mics of all kinds. It could have some valuable applications, although there's also the potential for misuse.
The university's Coordinated Science Laboratory states that the sound is produced by combining multiple tones that interact with a microphone's mechanical workings, creating what is known as a "shadow" – this is a type of white noise that is detectable only by the microphone, as it's formed within the mic itself.
Transmitted by ultrasonic speakers within a room, the sound could be used to keep confidential conversations from being clearly picked up by hidden listening devices. The people talking would still have no problem hearing each other, as the sound would be inaudible to them.
It could also thwart illegal audio recordings in movie theaters or music venues, plus it could be used in place of Bluetooth for wireless communication between Internet of Things (IoT) devices.
(Score: 0) by Anonymous Coward on Wednesday June 28 2017, @12:55PM
Where are these figures from? I'd assumed wideband ultrasonic noise [soylentnews.org] between 25 and 40kHz which would (if loud enough) hit around the resonant frequency of the membrane and send the mic into self-oscillation. As you state, it's simply impossible to reproduce the ultrasonics loud enough to prevent a recording via this method without risking physiological effects and then it's trivial to reduce the audible effect on the microphone and post process the recording.