Beat (acoustics)

This phenomenon is best known in acoustics or music, though it can be found in any linear system:"According to the law of superposition, two tones sounding simultaneously are superimposed in a very simple way: one adds their amplitudes".

Binaural-beat perception originates in the inferior colliculus of the midbrain and the superior olivary complex of the brainstem, where auditory signals from each ear are integrated and precipitate electrical impulses along neural pathways through the reticular formation up the midbrain to the thalamus, auditory cortex, and other cortical regions.

[6] According to a 2023 systematic review, studies have investigated some of the claimed positive effects in the areas of cognitive processing, affective states (like anxiety), mood, pain perception, meditation and relaxation, mind wandering, creativity, but the techniques were not comparable and results were inconclusive.

[7] Musicians commonly use interference beats objectively to check tuning at the unison, perfect fifth, or other simple harmonic intervals.

Italian composer Giacinto Scelsi, whose style is grounded on microtonal oscillations of unisons, extensively explored the textural effects of interference beats, particularly in his late works such as the violin solos Xnoybis (1964) and L'âme ailée / L'âme ouverte (1973), which feature them prominently (Scelsi treated and notated each string of the instrument as a separate part, so that his violin solos are effectively quartets of one-strings, where different strings of the violin may be simultaneously playing the same note with microtonal shifts, so that the interference patterns are generated).

Diagram of beat frequency
The sum (blue) of two sine waves (red, green) is shown as one of the waves increases in frequency. The two waves are initially identical, then the frequency of the green wave is gradually increased by 25%. Constructive and destructive interference can be seen.
A 110 Hz A sine wave (magenta; first 2 seconds), a 104 Hz G sine wave (cyan; following 2 seconds), their sum (blue; final 2 seconds) and the corresponding envelope (red)
Binaural beats
To experience the binaural beats perception, it is best to listen to this file with headphones on moderate to weak volume – the sound should be easily heard, but not loud. The sound appears to pulsate only when heard through both earphones. Time duration of 10 seconds
Binaural Beats Base tone 200 Hz, beat frequency from 7 Hz to 12.9 Hz. Time duration of 9 minutes.