Vowels are distinguished by the two lowest vocal tract resonance frequencies.

Evidence

Vowel sounds are characterized by voicing, which results in a spectrum with a fundamental frequency (F0), related to voice pitch, and harmonics of F0. The spectrum is shaped by vocal tract resonances, or formants. The locations of the lowest two frequency formants (F1 and F2), distinguish different vowel sounds (Fant 1960 ). — Dijk, Pim van, Physiology, Psychoacoustics and…, 5472

Categorization

• DEFINE: Provides baseline definitions of F0, formants, and F1/F2 needed to understand later coding details.