The noise peculiar to alveolar and dental consonants /t, d, s, z, n, l, , ð/ is contrasted with that of labial and labio-dental ones /p, b, m, f, v/ because it is sharper in character. This means that in the spectra of /t, d, s, z, n, l, , ð/ high frequencies are predominant and in the spectra of /p, b, m, f, v / the formant of noise is lower.