American English Phonetics

11.1 Fricatives and Voice

Fricatives are fully voiced when their articulation is accompanied by vocal cord vibration throughout the duration of the articulatory contact.

Devoiced fricatives are produced when there is vocal cord vibration during part of the duration of the narrowing only.

Voiceless fricatives are produced with a wide-open glottis, except for [h], for which glottal friction is produced by a narrowing in the glottis.