A binaural beat is an auditory illusion perceived when two different pure tone sine waves with slightly different frequencies are presented to a listener simultaneously through each ear.
For example, if a 430 Hz pure tone sine wave is presented to a subject's right ear, while a 410 Hz pure tone sine wave is presented to the subject's left ear, the listener will perceive the auditory illusion of a third tone, in addition to the two pure-tones presented to each ear.
The third sound is called a binaural beat which has a frequency equal to the difference in frequencies of the two waves presented to each ear. In the above example the binaural beat will have a frequency of 20 Hz which is equal to the difference between the 430 Hz and 410 Hz frequency of sound presented to each ear.
Binaural beats are claimed to influence the state of mind.
Binaural beats in the delta range have been associated with deep dreamless sleep and loss of body awareness.
Binaural beats in the theta range are linked to REM sleep, reduced anxiety, relaxation, as well as meditative states.
Binaural beats in the alpha frequencies are thought to encourage calm relaxed yet alert state.
Binaural beats in the beta frequencies have been linked to active, busy thinking, active processing , active concentration, arousal, and cognition.
Binaural beats in the gamma frequencies have been linked to higher mental activity, including perception, problem solving, and consciousness.