What are beats ?

Inacoustics, abeatis aninterferencebetween twosoundsof slightly differentfrequencies, perceived as periodic variations in volume whose rate is thedifferencebetween the two frequencies.
Withtuninginstruments that can produce sustained tones, beats can readily be recognized. Tuning two tones to aunisonwill present a peculiar effect: when the two tones are close in pitch but not identical, the difference in frequency generates the beating. The volume varies like in atremoloas the sounds alternately interfere constructively and destructively. As the two tones gradually approach unison, the beating slows down and may become so slow as to be inperceptible.