Work out beat frequency instantly with clear inputs, formula shown and shareable results.
Two close frequencies interfere to produce a slow amplitude pulsation at their difference frequency. 440 Hz against 444 Hz beats four times a second - one beat every 0.25 s - and the perceived pitch sits at the average, 442 Hz. Piano tuners use exactly this: they slow the beats to zero.
Beat frequency
f(beat) = |f1 - f2|
Musical interval
cents = 1200 log2(f2 / f1)
Because the difference frequency falls to zero. As tuning improves the beats slow until they stop, which is far more sensitive than judging pitch directly.
Above about 20 Hz difference the beating is no longer heard as pulsation but as roughness, and then as two separate tones.