Researchers hide data in music – and human ears can’t detect it

Researchers have developed a way for data to be secretly transferred inside a music track at a usable rate without turning it into unlistenable mush.

While using sound waves as a data carrier is not new, applying the principle to music has always been a challenge because even small distortions made when adding data will be noticed by the human ear.

If one could overcome this, music would make a good medium for data transfer because it can easily be picked up by the microphones used by smartphones and computers without annoying people by blasting unstructured sound at them.

How does it work?

The technique outlined by Manuel Eichelberger and Simon Tanner of ETH Zurich uses orthogonal frequency-division multiplexing (OFDM) to add data to the musical frequencies humans are less likely to notice whilst avoiding the ones they are sensitive to.

It sounds easy enough in principle but applying it to music tracks with individual harmonic compositions across different genres quickly becomes a highly technical challenge.

Then there’s the problem of being able to transfer enough data at a given distance to make the whole idea worthwhile.

After conducting experiments, the researchers found it was possible to achieve data rates of 300 to 400 bits per second (bps) over distances of up to 24 metres, with a 10% error rate, without affecting the original music when played to a test group of 40 people.

When a modified tune is played back by a speaker, a person listening to it cannot notice any degradation in sound quality but still, a smartphone is able to read out the information carried by the song.

What could you do with it?

Although a low data rate by modern radio frequency standards, the pair reckon this is still sufficient for basic applications, which brings us to the critical question of what such a data-in-music technology might be used for.

Their answer seems to make the everyday movement of small chunks of data such as security keys less of a manual chore. For example:

That would be handy in a hotel room, since guests would get access to the hotel Wi-Fi without having to enter a password on their device.

Granted, encoding useful data in music at bit rates and ranges not yet matched by other researchers is impressive, but to some this will sound like a solution looking for an application.

If something as compact as a Wi-Fi key could be transferred using sound waves, why not do that using a short blast of sound or simple sequence of musical notes?

Inevitably, using music creates the inherent problem of distortion while using sound at all depends on making assumptions about background noise.

Readers can judge for themselves by comparing the original track to the one with data added.

On a related note (pardon the pun), in 2015 another set of researchers from ETH Zurich suggested that comparing ambient sounds picked up by a smartphone and a PC to confirm they are in the same vicinity could be used for two-factor authentication.