Strident vowel

Strident vowels (also called sphincteric vowels) are strongly pharyngealized vowels accompanied by (ary)epiglottal trill, where the larynx is raised and the pharynx constricted, so that either the epiglottis or the arytenoid cartilages vibrate instead of the vocal cords. That is, the epiglottal trill is the voice source for these sounds.

Strident vowels are fairly common in Khoisan languages, where they contrast with simple pharyngealized vowels. Stridency is used in onomatopoeia in Zulu and Lamba.^[1] Stridency may be a type of phonation called harsh voice. A similar phonation, but without the trill, is called ventricular voice; both have been called pressed voice. The Bai language of southern China has a register system with allophonic strident and pressed vowels.

There is no official symbol for stridency in the IPA, though a superscript ⟨^ʢ⟩ (for a voiced epiglottal trill) is often used. In some literature a subscript double tilde (≈) is sometimes used, as seen here on the letter ⟨a⟩ (⟨a᷽⟩):

This has been accepted into Unicode at code point U+1DFD.

References

Ladefoged, Peter; Maddieson, Ian (1996). The Sounds of the World's Languages. Oxford: Blackwell. ISBN 0-631-19814-8. 

• Scott Moisik, Ewa Czaykowska-Higgins, & John H. Esling (2012) "The Epilaryngeal Articulator: A New Conceptual Tool for Understanding Lingual-Laryngeal Contrasts"