Strident vowels are strongly pharyngealized vowels accompanied by (ary)epiglottal trill

Epiglottal trill

In the epiglottal trill, the larynx is raised and the pharynx constricted, so that the epiglottis vibrates instead of the vocal cords. In the related aryepiglottal trill, the arytenoid cartilages vibrate....

, where the larynx

Larynx

The larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...

 is raised and the pharynx

Pharynx

The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

 constricted, so that either the epiglottis or the arytenoid cartilage

Arytenoid cartilage

The arytenoid cartilages are a pair of small three-sided pyramids which form part of the larynx, to which the vocal folds are attached...

s vibrate instead of the vocal cords.

Strident vowels are fairly common in Khoisan languages

Khoisan languages

The Khoisan languages are the click languages of Africa which do not belong to other language families. They include languages indigenous to southern and eastern Africa, though some, such as the Khoi languages, appear to have moved to their current locations not long before the Bantu expansion...

, where they contrast with simple pharyngealized vowels. Stridency may be a type of phonation

Phonation

Phonation has slightly different meanings depending on the subfield of phonetics. Among some phoneticians, phonation is the process by which the vocal folds produce certain sounds through quasi-periodic vibration. This is the definition used among those who study laryngeal anatomy and physiology...

 called harsh voice

Harsh voice

Harsh voice, also called ventricular voice or pressed voice, is the production of speech sounds with a constricted laryngeal cavity, which generally involves epiglottal co-articulation...

. A similar phonation, but without the trill, is called pressed voice or ventricular voice. The Bai language of southern China has a register

Register (phonology)

In linguistics, a register language, also known as a pitch-register language, is a language which combines tone and vowel phonation into a single phonological system. Burmese and the Chinese dialect Shanghainese are examples...

 system with allophonic

Allophone

In phonology, an allophone is one of a set of multiple possible spoken sounds used to pronounce a single phoneme. For example, and are allophones for the phoneme in the English language...

 strident and pressed vowels.

There is no official symbol for stridency in the IPA

International Phonetic Alphabet

The International Phonetic Alphabet "The acronym 'IPA' strictly refers [...] to the 'International Phonetic Association'. But it is now such a common practice to use the acronym also to refer to the alphabet itself that resistance seems pedantic...

, though a superscript ^ʢ is often used. In some literature a subscript double tilde (≈) is sometimes used, as seen here on the letter ‹a› (a):



This is found in the Charis

Charis SIL

Charis SIL is a glyphic serif typeface developed by SIL International. It is based on Bitstream Charter, one of the first fonts designed for laser printers...

 and Doulos

Doulos SIL

Doulos SIL is a serif typeface developed by SIL International, very similar to Times or Times New Roman. Unlike Times New Roman, Doulos only has a single face, Regular...

 fonts (a), and has been accepted into Unicode

Unicode

Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...

at code point U+1DFD.