Beat Frequency Calculator
Enter two sound wave frequencies to calculate the beat frequency and see the audible pulsing rate instantly. This free browser tool needs no signup or install.
What Are Beat Frequencies?
When two sound waves of slightly different frequencies interfere, you hear a pulsing volume change called beats. Musicians use beats to tune instruments: when beats slow to zero, the notes match.
Beat Frequency Formula
$$f_{\text{beat}} = |f_1 - f_2|$$The beat period is the time between successive loud points:
$$T_{\text{beat}} = \frac{1}{f_{\text{beat}}}$$Example: 440 Hz and 444 Hz produce a 4 Hz beat, so you hear four pulses per second and the beat period is 0.25 s.
Practical Tuning
Piano tuners listen for beats between a reference pitch and the string being adjusted. As the string approaches the target frequency, beats become slower and disappear when frequencies match.
Related tools: Note Frequency Calculator and BPM Calculator.
Frequently Asked Questions
Why absolute value in the formula?
Beats occur at the same rate whether \(f_1\) is higher or lower than \(f_2\). Only the difference matters.
What if the frequencies are equal?
Beat frequency is zero and the tone is steady. There is no periodic amplitude modulation.
Can beats happen with light?
Yes. Optical heterodyning uses the same mathematics with electromagnetic waves at much higher frequencies.
How close must frequencies be to hear beats?
Human hearing resolves beats best when the difference is under about 15 Hz. Larger gaps sound like two separate tones.
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