The theory behind binaural beats is that if you apply slightly different frequency sine waves to each ear, a beating affect is created in the brain itself, due to the brain's internal wiring. If, in the presence of these tones, you relax and let your mind go, your mind will naturally synchronize with the beat frequency. In this way it is possible to tune the frequency of your brain waves to particular frequencies that you have selected, using of the four bands: Delta: deep sleep, Theta: dreaming and intuitive stuff, Alpha: awake, focussed inside, and Beta: awake, focussed outside .....(free).....