Sound that is audible only to microphones developed

Urbana, Illinois: Microphones, from those in smartphones to hearing aids, are built specifically to hear the human voice — humans can’t hear at levels higher than 20 kHz, and microphones max out at around 24 kHz, meaning that microphones only capture the sound we can hear with our ears.

However, researchers at the Coordinated Science Laboratory have designed a sound that is completely inaudible to humans (40kHz or above) yet is audible to any microphone. The sound combines multiple tones that, when interacting with the microphone’s mechanics, create what researchers call a “shadow,” which is a sound that the microphones can detect.

The team, which includes PhD student Nirupam Roy and CSL Professors Romit Roy Choudhury and Haitham Hassanieh, see many applications for this work. This work won Best Paper Award, titled “BackDoor: Making Microphones Hear Inaudible Sounds,” at a leading conference, MobiSys 2017.

“Imagine having a private conversation with someone. You can broadcast this inaudible signal, which translates to a white noise in the microphone, to prevent any spy microphones from recording voices,” said Roy, a PhD student in electrical and computer engineering. “As it’s inaudible, it wouldn’t interfere with conversation.”

Researchers say army and governments could secure confidential meetings from electronic eavesdropping or cinemas and concerts could prevent unauthorised recording of movies and live performances.