Audio Beat Frequency Calculator

Beat frequency between two coupled tones: formula and example

Play two pitches that sit close together and you’ll hear the loudness swell and fade at the beat frequency f_beat = |f1 − f2|. Run 440 Hz vs 442 Hz → 2 Hz and you land on two amplitude pulses a second. Push them to 440 vs 440.5 Hz and it slows to a 0.5 Hz wobble; widen the gap to 440 vs 446 Hz and the 6 Hz beat starts to sound like a rough tremolo.

Context and applications

Piano and guitar tuners rely on this. They line up string pairs and unisons by listening for the beat, and once it vanishes the strings are in tune. In an orchestra, players settle on A=440 by shaving down the beats they hear against the oboe. The same trick shows up in microtonal music, where slow beats become part of the texture, and in psychoacoustics: under about 20 Hz the ear reads the result as one fluctuating tone, while past roughly 30 Hz it tips into roughness or splits off into a separate difference tone.

FAQ

Why do beats happen? Add two sinusoids of nearly equal frequency and the result is a single wave whose amplitude is modulated at half the difference frequency. Even so, the ear ends up counting |f1 − f2| pulses per second.

How small a beat can a tuner hear? A trained ear can pick out beats slower than 1 Hz, roughly 2 cents at A4. Strobe tuners reach much finer, down to about 0.1 cent.

Beats vs difference tones? Under about 20 Hz you get a beat. Above that, the brain may build a separate difference tone at |f1 − f2|, what musicians call a Tartini tone.