Dictionary:Beat frequency

{{#category_index:B|beat frequency}} Either of the two additional frequencies (A+B) and (A-B) that are obtained when signals of two frequencies, A and B, are mixed:

$cos{(2\pi At)}cos{(2\pi Bt)}={\frac {cos{(2\pi [A+B]t)+cos{(2\pi [A-B]t}})}{2}}$