Artificial Wasteland · a question the internet answers badly
The Pitch You Didn't Change
Everyone knows helium makes your voice squeaky. Almost everyone says it's because helium is "lighter," so your pitch goes up. That's wrong — and you can hear exactly why. Helium leaves your pitch alone and slides your timbre up instead. Below are the two knobs, pulled apart. Move them.
pitch 120 Hz timbre shift ×1.00 sound speed 343 m/s
Changes the comb spacing. The formants don't budge.
Slides the formants. The pitch (comb) doesn't budge.
Sound is off until you press play. It's a synthesised source–filter model of a voice (a buzz through a tube); the picture is a schematic of the same source/filter model.
What just happened. The thin blue lines are a harmonic comb: your vocal folds buzz at some rate F0, and the buzz contains that frequency plus every multiple of it. That comb is your pitch. The glowing gold humps are the formants — the resonances of the tube of air between your voice box and your lips, which amplify some frequencies and damp others. The comb is the source; the humps are the filter. In this model, helium only touches the filter.
Why? In an ideal cavity of fixed shape, with rigid walls and ideal open ends whose boundary conditions do not change with the gas, resonance frequencies scale with the speed of sound. Helium is a light, monatomic gas, so sound travels through pure helium about 2.9× faster than through air at the same temperature. Every formant in this ideal model shifts by that factor; real-tract scaling is approximate. Drag the gas slider and watch the humps march right while the comb stays nailed in place. Your ear hears the brighter, top-heavy timbre and reports it as "higher pitch," but the pitch — the comb — never moved. That mis-hearing is the whole illusion.
In practice the helium mixes with gas already in your lungs, and the composition and formant shifts vary. The button uses an illustrative 80/20 helium-air mix, which gives about a 1.9× shift in this ideal model. Hit "snap to an illustrative 80% helium mix" to land there. And the trick runs both ways: a heavy gas like sulfur hexafluoride makes sound slow down, formants drop, and you get the cartoonish "demon voice" — same physics, opposite sign.
The check — show, don't assert
These ideal-gas and tube-model values are recomputed by
research/helium-voice/verify.mjs (18 model checks, including a stated
source/filter independence assumption). The speed of sound is c = √(γRT/M);
the neutral-vowel formants of an ideal 17.5 cm rigid tube, closed at one end and open at
the other, are Fn = (2n−1)·c / 4L.
| at 20 °C | air | helium | × |
|---|---|---|---|
| speed of sound | 343 m/s | 1007 m/s | 2.94 |
| F1 (formant 1) | 490 Hz | 1439 Hz | 2.94 |
| F2 | 1471 Hz | 4318 Hz | 2.94 |
| F3 | 2452 Hz | 7196 Hz | 2.94 |
Proven within the model: the speed ratio is √((γHe/γair)(Mair/MHe)) ≈ 2.94,
independent of the common temperature with these ideal-gas constants. Every resonance
scales by exactly that ratio for fixed geometry with rigid walls and ideal open ends,
provided those boundary conditions do not change with the gas. Under those assumptions,
the resonance condition depends on frequency and sound speed through f/c,
whatever the cavity's shape. The illustrative 80/20 helium-air mixture gives ~1.9× in
this model; sulfur hexafluoride gives 0.39× (the opposite effect).
Named uncertainty: the claim that the pitch itself (F0) barely moves is physiological, not derived here — F0 is set by vocal-fold tension and mass, which is why no formula on this page contains it. The literature reports a small F0 change (a few percent, direction debated); reduced gas loading of the folds is one possible contributor. That small real effect is not the cause of the squeaky voice; the formant shift is. The vocal tract is modelled as a uniform tube for the headline numbers. Real formants vary with the vowel (try the vowel buttons), and real tract walls are not rigid. Exact scaling for different shapes belongs to the ideal boundary conditions above; in a real tract the scaling is approximate.
The one-sentence answer
Helium doesn't make your voice higher in pitch — it makes it brighter, by speeding up sound and shoving your vocal tract's resonances upward, and your ear mistakes that brightness for pitch.
Is it dangerous? (the honest aside)
A quick squeak from a party balloon is generally low-risk, but inhaling helium is not free: helium displaces oxygen, so a deep lungful (or, worse, gas straight from a pressurised tank) can cause hypoxia, fainting, or — at tank pressure — lung injury and gas embolism, which can be fatal. The physics is fun; the safe way to enjoy it is to understand it, not to keep inhaling. This page is here so you don't have to.
Corrections
Corrected 2026-10-14: This page said every real vocal-tract formant scaled exactly with the gas's sound speed. Exact scaling belongs to a fixed ideal cavity with rigid walls and ideal open ends whose boundary conditions do not change with the gas; real-tract scaling is approximate (found by the assay line, 2026-10-14). Duncan (1983), pp. 42-43 and 52.
Corrected 2026-10-14: This page called an 80/20 helium-air mix and its roughly 1.9× shift a realistic balloon breath. That mixture is an illustrative preset, and 1.91× is its ideal-model result; actual tract mixtures and formant shifts vary (found by the assay line, 2026-10-14). The Science of Sound, p. 359.