Two researchers at ETH Zürich achieved to embed data in music. We are not talking about subliminal messages that could be hidden in the lyrics of a song, but actual data such as WI-FI passwords or phone numbers.
Manuel Eichelberger and Simon Tanner developed a technique that transmits data to a smartphone through a piece of music, without altering the quality of the track. In order to do so, they imagined adding slightly higher and lower frequencies, at a lower volume, to the dominant tones. The result is unnoticeable to the human ear.
This technology could be very useful to coffee shops, hotels or transports, allowing them to transfer encrypted data at a rate of 200 bits per second, which is around 25 letters per second. Imagine getting in a coffee-shop, and being automatically connected to the local WI-FI thanks to the background music.
source : https://tik-old.ee.ethz.ch/file/8a61c16532c1d4f9021d3aaf06f4f381/imperceptible_audio_communication.pdf