i want to know about beat frequency

When two sound waves of different frequency approach your ear, the alternating constructive and destructive interference causes the sound to be alternatively soft and loud - a phenomenon which is called "beating" or producing beats. The beat frequency is equal to the absolute value of the difference in frequency of the two waves.

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Freind, It''s Simple

Suppose a source A emits the sound of frequency K , and another source emits a frequency close to K say K-2, so when these sound waves superpose each other you get to hear a frequency K-(K-2)= 2 hertz, which is a result of constructive and destructive interference of two sound waves of slightly different frequency.

you can try out this on your pc by following this link.

http://upload.wikimedia.org/wikipedia/commons/6/6f/Terzosuono.ogg

here the beat frequency is increased gradually. 

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