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Beat frequency demo: hear the 4 Hz wobble from 440 + 444 Hz

By TechCompare · Updated · How we check

Play 440 Hz and 444 Hz together and you'll hear a 4 Hz amplitude wobble. The beat frequency always equals the absolute difference between the two sources. That's how ear-tuning works.

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Frequency Generator

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2 oscillators: 440 + 444
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A beat frequency is the slow pulsing you hear when two tones of nearly equal frequency play together. Two sines at 440 Hz and 444 Hz produce a beat at 4 Hz. The amplitude swells and dips four times per second. The beat equals the absolute difference between the two source frequencies.

It's a basic interference effect in acoustics, and a frequency generator lets you hear it cleanly without the noise music adds.

Oscillators
2
2 stacked tones
Frequencies
440 Hz + 444 Hz
Waveform
Sine
Summed view

How this is calculated

The math is direct: when two sines of slightly different frequencies combine, their sum is a tone at the average frequency, amplitude-modulated at the difference frequency. So 440 + 444 sounds like a 442 Hz tone whose loudness pulses 4 times per second.

This is why tuning by ear works: a guitar string slightly off from a reference produces a slow beat, and you tune until the beat slows to zero. You can also hear beats between any two close sources: two out-of-tune orchestral players, two synth oscillators, even the two tines of a tuning fork that's been slightly bent.

Move the slider on the lower oscillator and you'll hear the beat speed up as the frequency difference grows.

Verdict

Listen first, then switch to the summed view to watch the 4 Hz beat on the waveform. Hearing and seeing the beat together makes it easy to remember that it equals the gap between the two tones.

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Room resonance, also called room modes, is the standing wave pattern that forms in any enclosed space at low frequencies.
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Headphone rattle
A headphone rattle test isolates buzzing that music masks.
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Related guides

1 kHz reference tone
The companion reference tone for beating comparisons at 1 kHz.
View guide
A4 = 440 Hz tuning reference
Where beats vanish: the concert pitch this reference tone defines.
View guide

Frequently asked questions

What is a beat frequency?
A beat frequency is the slow amplitude pulsing you hear when two tones of nearly equal frequency play together. The beat equals the absolute difference between the two frequencies. Two sines at 440 and 444 Hz produce a 4 Hz beat.
How do you calculate beat frequency?
Beat frequency equals |f1 - f2|. If one tone is 440 Hz and the other is 444 Hz, the beat is 4 Hz. The two sines combine into a wave at the average frequency (442 Hz) whose amplitude is modulated at the difference (4 Hz).
Why are beat frequencies useful for tuning?
When two close tones are perfectly in tune, the beat disappears. Tuning by ear works by adjusting until the beat slows to zero. The faster the beat, the further out of tune you are.

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