This professional Binaural Beats app can help put your brain into various states by stimulating the left and right auditory cortex with differential frequencies. Using 2 slightly different pitches of sound in each ear, the difference produces a noticeable pulsing sensation in the brain, which encourages brain waves of that frequency. Choosing the right pulse frequency can promote relaxation, increase focus, aid sleep, or a number of different effects. Because the effect requires a different frequency played in each ear, you need to listen with headphones.