Vowels often have been characterized by the first 3 formants.
Lax vowels have long off glides and short steady states.
A rough rule of thumb in relating the vowel formant frequencies to vowel articulation is that F1 varies mostly with tongue height and F2 varies mostly with tongue advancement. A vowel s formant pattern can be used to identify a vowel and even to establish relationships between acoustic and perceptual parameters. Back vowels have a low F2 and typically a small F2-F1 difference. Vowel Spectrum Vowels can be described with respect to their spectra. In general, any spectral variation that affects the location of a peak can seriously affect the phonetic interpretation of the vowel spectrum.