Beating is a frequency effect that occurs in acoustics and RF technology when two oscillations are emitted whose amplitudes are approximately equal and whose frequencies differ only slightly. The listener cannot distinguish the individual tones from one another; he hears a single tone that is the result of the frequency average of the two individual tones and that swells and diminishes in volume.
In this phenomenon, a new oscillation arises from the two individual tones, whose frequency approximately corresponds to that of the two individual oscillations and whose amplitude changes periodically. The amplitudes of the two frequencies add up at some times and cancel each other out at others. This effect is called beat.
The beat frequency corresponds to the average value of the two fundamental frequencies, the amplitude fluctuates in the rhythm of the beat frequency and results from the difference of the two fundamental frequencies. The beat sensation remains only as long as the beat frequency - the difference frequency of the two fundamental frequencies - is not more than about 20 Hz. After that, the beat changes to the effect of roughness.