Binaural Beats

Binaural beats are utility recordings built on an auditory illusion: when two pure tones of slightly different frequency are presented separately to the left and right ears through headphones, the brain perceives a third, pulsing tone equal to the difference between them. *Robert A. Monroe* patented the technique as Hemi-Sync in 1975 and built the #Monroe Institute#'s Gateway Experience around progressions of such tones, which producers align with brainwave bands — delta for sleep, theta for meditation, alpha for relaxed focus. The recordings are functional audio, marketed for states of mind rather than for musical content.