Tools / Physics
100% client-side — no data leaves your browserBeat Frequency Calculator
When two tones sound together, you hear beats at fbeat = |f₁ − f₂|. Compute the beat rate, the beat period, or work backwards to find an unknown tone — the classic tool for tuning instruments by ear.
You know one tone and you hear (or measure) the beat rate. The unknown tone has two possible values: f₂ = f₁ ± fbeat — the beat alone cannot tell you whether it is above or below the known tone.
Worked examples (computed by this page's engine)
Frequently asked questions
What is beat frequency?
Beat frequency is the pulsing rate you hear when two tones of slightly different frequency sound together. It equals the absolute difference of the two frequencies: f_beat = |f1 - f2|. For example, 440 Hz and 443 Hz sounded together produce a beat frequency of 3 Hz - three loud-soft pulses per second.
How do you calculate beat frequency?
Subtract the lower frequency from the higher one (or take the absolute value of the difference). Example: two tuning forks at 512 Hz and 516 Hz give f_beat = |512 - 516| = 4 Hz. The order does not matter: |f1 - f2| is symmetric.
What is the beat period?
The beat period is the time between two successive loud pulses: T = 1 / f_beat. A 3 Hz beat has a period of 1/3 s = 333.333 ms; a 4 Hz beat has a period of 250 ms; a slow 0.25 Hz beat has a period of 4 s.
I know one tone and the beat rate. What is the other tone?
There are two possible answers: f2 = f1 +/- f_beat. If the known tone is 440 Hz and you hear a 3 Hz beat, the unknown tone is 437 Hz or 443 Hz. This ambiguity is fundamental - a beat rate alone cannot tell you whether the unknown tone is above or below the known one.
Why does beating sound like the loudness is pulsing?
The two sound waves interfere: they alternately reinforce (loud) and cancel (soft) each other. The reinforcement repeats f_beat times per second. This description assumes ideal sine waves; real instruments add harmonics, but the pulse rate still follows |f1 - f2|.
Can I use beats to tune a guitar or piano?
Yes - it is the classic ear-tuning method. Play a 440 Hz reference against your string: if you hear a 3 Hz beat (180 beats per minute), the string is 3 Hz off. Adjust until the pulsing slows to zero. It works best when the two tones are close; a large difference beats too fast to count.
Can beat frequency be zero?
Yes. When f1 equals f2 the tones are in unison, f_beat = 0, and there is no pulsing at all. The beat period is undefined in that case because there is no beating.
What units are used for beat frequency?
Hertz, like any frequency. This calculator also shows kilohertz and beats per minute: a 3 Hz beat equals 0.003 kHz and 180 BPM (3 x 60).
What is the difference between this calculator and a frequency converter?
This page computes interference between two frequencies (f_beat = |f1 - f2|) - a physics phenomenon. A frequency converter only changes units (Hz to kHz, MHz, rpm, rad/s). For unit conversion, wavelength, Nyquist rate and band lookup, use the Frequency Converter hub instead.
What happens when the beat rate is fast, like 25 Hz?
You stop hearing distinct pulses. Around 15-30 Hz the beats blur into roughness, and faster still they are perceived as dissonance rather than pulsing. Clear, countable beats live roughly below 7 Hz - the range tuners rely on.
Does beat frequency work at radio frequencies too?
The same law holds at any scale. Two carriers at 2.4 GHz and 2.400001 GHz differ by 1000 Hz, so their beat (difference) frequency is 1 kHz - the principle behind heterodyne receivers.
What does a very slow beat look like?
Tones at 100 Hz and 100.25 Hz produce f_beat = 0.25 Hz: a single gentle swell of loudness every 4 seconds. Very slow beats are useful for fine-tuning to unison.
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