To achieve this, the ETH team's technology plays two major tricks.įirst, they harness a property of the human auditory system called psychoacoustic masking, in which the ear cannot discern some sounds if they are within a certain range (called the critical bandwidth) of high amplitude (louder) sounds. However, the ETH researchers were not seeking secrecy: its aim is to embed useful data in music tracks in a way that is as audibly unobtrusive as possible, and at a high data rate.
Play that data through speakers, though, and the error rate is so high, it is not possible to reconstruct the digital message accurately. These files are normally used in digital "steganography" applications: the hiding of data in plain sight to keep messages secret, such as illicit bank account numbers or encryption keys. The ETH team was not starting with a blank slate, however people have hidden data in music before (but they have hidden it amongst the 0s and 1s of computer music files, rather than in the sound emitted by a loudspeaker). The researchers wondered if they could use sound to make it easier for people to set up such links, which they described as "a hassle in countless ad hoc communications situations." In research presented at the ACM HotMobile conference in Santa Cruz, CA, in February, the ETH team revealed its response to the problem: a smart method of encoding data in music such that it cannot be heard.
Music spectrograph data Bluetooth#
This sonic feat has been made possible by a team of acoustics engineers at ETH Zurich, the Swiss Federal Institute of Technology in Zurich, who used a technique normally used to prevent interference in digital radio broadcasts and 4G signaling to conceal data streams in music played over loudspeakers.ĮTH researchers led by Manuel Eichelberger and Simon Tanner were inspired in part by an XKCD comic strip (see below) highlighting just how complicated it remains, more than 20 years after the advent of Wi-Fi and Bluetooth appeared, to pair phones with wireless routers and Bluetooth devices you have never encountered before while on the move. A spectrogram of the song Nannou by Aphex Twin yields this image of the performing artist.ĭata buried deep within the background music played in cafes, shops, sports venues and airports could soon be providing a raft of new services to smartphone users, such as seamlessly pairing phones with wireless or Bluetooth networks, or receiving flight updates or sports news and stats when cellphone networks are swamped with too many users.
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