Beats (Two Close Frequencies)
Play two tones a few hertz apart and watch the combined wave swell and fade — the beat you hear is the difference between the two frequencies, and you can tune it to zero.
Preview — sign up free to change the numbers yourself
What you can adjust
- Tone 1 frequency (f₁)
- 200 – 600 Hz
- Tone 2 frequency (f₂)
- 200 – 600 Hz
- Tone 2 amplitude (relative to tone 1)
- 0.2 – 1
- Duration
- 0.5 – 3 s
The first tone's frequency. 440 Hz is concert pitch A4.
The second tone's frequency. Tune it close to f₁ to slow the beat down — set it equal to f₁ and the beat disappears entirely.
How loud tone 2 is compared to tone 1. At 1.0 (matched volumes) the combined wave fades all the way to silence at each beat node; a quieter tone 2 leaves some wave left over even at the quietest point.
How much time to draw. A longer window shows more full beat cycles when the two tones are close together.
About this simulation
What it shows
Two tones with nearly the same pitch are added together, and the combined wave swells and fades. The beat rate is read out.
The key idea
Two close frequencies drift in and out of step, so their sum gets louder and quieter at a rate equal to the difference between them, |f₁ − f₂|. Equal frequencies give no beat at all.
Try this
Change Tone 2 frequency (f₂) from 444 Hz to 442 Hz: the beat slows from 4 per second to 2 per second, and at 440 Hz it disappears.