Imperceptible Audio Communication

A differential acoustic OFDM technique is presented to embed data imperceptibly in existing music. The method allows playing back music containing the data with a speaker without users noticing the embedded data channel. Using a microphone, the data can be recovered from the recording. Experiments with smartphone microphones show that transmission distances of 24 meters are possible, while achieving bit error ratios of less than 10 percent, depending on the environment. Furthermore, we present a user study which shows that many people do not recognize the added data channel in music, even when being informed about the experiment and therefore actively listening for the data transmission. Depending on the source music, data rates of 300 to 400 bits per second are achieved.