Editing Wave interference (section)

===Beat===
{{Main|Beat (acoustics)}}
In [[acoustics]], a '''beat''' is an [[Interference (wave propagation)|interference]] pattern between two [[sound]]s of slightly different [[frequency|frequencies]], ''perceived'' as a periodic variation in [[amplitude (music)|volume]] whose rate is the [[Difference (mathematics)|difference]] of the two frequencies.

With [[Musical tuning|tuning]] instruments that can produce sustained tones, beats can be readily recognized. Tuning two tones to a [[unison]] will 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 a [[tremolo]] as 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 imperceptible. As the two tones get further apart, their beat frequency starts to approach the range of human pitch perception,<ref>{{Cite book|title=This is Your Brain on Music: The Science of a Human Obsession|last=Levitin|first=Daniel J.|publisher=Dutton|year=2006|isbn= 978-0525949695 |page=22}}</ref> the beating starts to sound like a note, and a [[combination tone]] is produced. This combination tone can also be referred to as a [[missing fundamental]], as the beat frequency of any two tones is equivalent to the frequency of their implied fundamental frequency.