Vowel chart · F1 × F2
F0 120 Hz
F1 0 Hz
F2 0 Hz
F3 0 Hz
Velum closed
Closest reference vowel: /ɛ/ head
Controls
Or just hold down on the chart (mouse or finger).
Drag the dot around the vowel chart and listen. The buzz from the vocal folds sets the pitch (F0); the shape of the mouth sets the resonances (F1, F2, F3) that make one vowel sound different from another.
The vocal folds open and close F0 times a second. That buzz holds energy at every whole-number multiple of F0 (the harmonics), each a bit weaker than the last. F0 is what you hear as pitch. Move the F0 slider and watch the harmonic lines spread apart while the filter curve stays put.
The throat and mouth form a tube with resonances, called formants. Harmonics near a formant come out loud and the rest are damped. F1 rises as the jaw opens and the tongue drops, so it tracks vowel height in reverse. F2 rises as the tongue moves forward, so it tracks frontness.
F3 matters less for telling most vowels apart, but it drops with lip rounding and plunges for r-colored vowels. Click /ɝ/ ("heard") and it snaps F3 to about 1690 Hz. Then drag F3 back up to 2500 with F1 and F2 unchanged and the r-quality goes away.
Lowering the velum opens a side branch into the nose. That adds a low nasal peak near 250 Hz and an antiresonance (a notch) that climbs through the F1 region, and it widens F1. F2 and F3 barely move. Pick /ɑ/ or /ɛ/, hold the sound on, and slide the velum up for /ɑ̃/ or /ɛ̃/ as in French blanc and vin.
Pick /i/ ("heed"), then raise F0 to 300 Hz. The harmonics are now so far apart that the lowest one sits above F1, and the filter shape gets sampled only a few times. That is one reason sung vowels from sopranos are hard to identify.