Hemi-sync is a technology developed by Robert Monroe, founder of the Monroe Institute. Hemi-sync is short for Hemispheric Synchronization aka Brainwave synchronization. Monroe claimed that the technique synchronizes the two hemispheres of one's brain, thereby creating a 'frequency-following response' designed to evoke certain effects. Hemi-sync can allegedly be used for many purposes, including relaxation and sleep induction, learning and memory aids, helping those with physical and mental difficulties, and reaching altered states of consciousness through the use of sound.
Hemi-Sync is a scientifically and clinically proven audio-guidance process that works quite simply by sending different sounds (tones) to each ear by stereo headphones. This process is perfectly safe and non-intrusive, which also means no subliminal messages are used. Any verbal cues are clearly stated and understood. The two hemispheres of the brain then act in unison to “hear” a third signal - a Binaural Beat - the difference between the two tones. This is not an actual sound, but an electrical signal that can only be perceived within the brain when both brain hemispheres are working together.