Binaural beats

A binaural beat is an auditory illusion. It is perceived when two different pure-tone sine waves are presented to a listener, one tone to each ear. 
For example, if a 530 Hz pure tone is presented to a subject's right ear, while a 520 Hz pure tone is presented to the subject's left ear, the listener will perceive the illusion of a third tone. The third sound is called a binaural beat, and in this example would have a perceived pitch correlating to a frequency of 10 Hz, that being the difference between the 530 Hz and 520 Hz pure tones presented to each ear.
They may help people with pain when they are in hospital. Some people use binaural beats to help them sleep, meditate or have out of body experiences. There are computer programs and smartphone programs that make binaural beats.
Many of the claims are not verified at present.
History.
Heinrich Wilhelm Dove (18031879) discovered binaural beats in 1839 and published his findings in the scientific journal "Repertorium der Physik". While research about them continued after that, the subject remained something of a scientific curiosity until 134 years later, with the publishing of Gerald Oster's article "Auditory beats in the brain" ("Scientific American", 1973). Oster's article identified and assembled the scattered pieces of relevant research since Dove, offering fresh insight (and new laboratory findings) to research on binaural beats.
Oster saw binaural beats as a powerful tool for cognitive and neurological research. Unsolved questions include how animals locate sounds in their environment: the remarkable ability of animals to pick out and focus on specific sounds in a sea of noise (known as the ).