Binaural beats or binaural tones are auditory processing artifacts, or apparent sounds, the perception of which arises in the brain for specific physical stimuli. This effect was discovered in 1839 by Heinrich Wilhelm Dove, and earned greater public awareness in the late 20th century based on claims that binaural beats could help induce relaxation, meditation, creativity and other desirable mental states. The effect on the brainwaves depends on the difference in frequencies of each tone: for example, if 300 Hz was played in one ear and 310 in the other, then the binaural beat would have a frequency of 10 Hz.
In addition to being a neat effect, there are claims that it can be used as a relaxation tool via brainwave synchronization. The frequencies selected here, 4Hz and 7Hz, are very popular binaural beats because they correspond to theta waves, which again are associated with relaxation and meditation.