In physics, the pulsation resulting from a combination of two waves of slightly different frequency. Beat frequency is the difference between the frequencies of the combining waves. When the interfering frequencies are in the audible range, the beats are heard as alternating soft and loud pulses. The human ear can detect beats with frequencies up to 10 hertz, or 10 beats per second. Piano tuners listen for beats when comparing the pitch of a tuning fork to that of a vibrating string; when no beats are heard, the fork and string are at the same frequency. Ultrasonic or inaudible frequencies can be superimposed to produce audible beats, allowing the detection of vocal sounds produced by bats or dolphins.

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