A song plays in a crowded supermarket. To some people, this is just background music. But others can take out their smartphones and discover that implanted in the music is information, maybe a Wi-Fi password or a website URL. The scene is the vision put forward by Simon Tanner from the Swiss Federal Institute of Technology.
"The whole idea is basically that we can send data locally without any setup," Tanner explained, "We don't have to type any passwords or pair devices or anything like that. We just have speakers that can broadcast data along with a song and anyone in range could access it." He also discovered not all music is created equal when it comes to data. It's easier to hide it on songs with more distracting loud notes.
If data wasn't hidden and was just put into a song, it might sound like random static (静电噪声) or a series of unpleasant sounds. But Tanner's program looks at very small parts of the song, and analyzes which tones are most dominant (支配的). Then data is added to the dominant tones. Because the data is now masked in the dominant tones, the song doesn't sound different to the human ear, but it does to a microphone.
Now, the data is transferred in about 200 bits(比特，存储单位) per second, which could be the length of a Wi-Fi password, or a short message. As the research continues to mature, the amount of data that can be stuffed into a song will likely expand to 1120 bits, which is the length of a standard text message.
But this will never be a system for mass data sending. For one thing, the more data you put into a song, the more noticeable it comes and the more difficult it is to hide. For another, this system of placing data in music isn't quicker than current ones. And it isn't the most secure system. Anyone in the room could receive the data with the app.
