In physics and sound, a beat is the oscillation between zero intensity and full intensity that occcurs when two frequencies (which are not harmonically related) are added together, caused by alternating constructive and destructive interference of the pressure waves. Beating is heard as a pulsation in loudness of two nearby frequencies, f1 and f2, at the rate of |f1 − f2|. Thus f = 0 when the two waves are in unison and as the difference between f1 and f2 increases, the speed decreases till beyond a certain proximity beating stops and a roughness is heard instead, after which the two pitches are perceived as separate. Beating can also be heard between notes that are near to, but not exactly, a harmonic interval. The composerAlvin Lucier has written many pieces which feature interference beats as their main focus. Musicians commonly use interference beats to objectively check tuning at the unison, perfect fifth, or other simple harmonic intervalss.
In music, beat is any of the periodic transient signals in music that mark the rhythm. In particular, it can and often does take the form referred to above, caused by alternating constructive and destructive interference of sound waves.
Beat can also mean solely the bass and snare drums of the rhythm. DJs often beatmatch the songs that they play.
Interference beats are used in tuning, see tuning and physics above.
