MusicReasonPitch, Tuning, Intonation, and Fret Geometry
How fast do these two tones beat?
Enter two frequencies. This tool calculates the acoustic beat rate between them, the exact difference in Hz, plus the resulting period and cents distance. It does not model complex spectra, masking, or perceived roughness, only the pure-tone beat rate itself.
Answer
Want to learn more? Tuning, Cents, Temperament, and Reference Pitch
Understand
When two pure tones sound together at nearly the same frequency, their combined amplitude rises and falls at a rate equal to the difference between the two frequencies. Below about 20 Hz that rise and fall is heard as a pulsing rhythm; above it, the ear starts to perceive the beating as a rough, dissonant tone rather than a separate rhythm.
Worked examples
440 Hz and 442 Hz beat at exactly 2 Hz, one full pulse every 0.5 seconds. Two identical frequencies produce zero beating, an explicit zero rather than an undefined or infinite rate, since equal frequencies simply do not interfere with each other at all.
Method and limitations
The beat rate is the absolute difference between the two stated frequencies; its period is one divided by that rate, undefined (shown as no period) only when the rate is exactly zero. The cents distance between the two frequencies is reported alongside it for tuning context, since a very small beat rate at a low pitch can still represent a meaningfully large cents difference. This tool assumes pure sine tones; real instrument tones carry overtones that can beat against each other independently of the fundamentals, which this simple model does not capture.
This is exactly the effect a piano tuner exploits when tuning by ear: bringing a string closer to a target pitch slows the audible beating between it and a reference tone until the beats disappear entirely at a perfect unison, or settle into a stable, deliberately chosen rate for a tempered interval. Two frequencies barely a cent or two apart at a low pitch can still beat slowly enough to count as a genuinely useful tuning reference, even though the beat rate itself, in Hz, looks tiny next to the frequencies producing it.