[1][2] Either the epiglottis or the arytenoid cartilages thus vibrate instead of the vocal cords.[3][page needed] Stridency may be a type of phonation called harsh voice.[citation needed] Bai, of southern China, has a register system that has allophonic strident and pressed vowels.There is no official symbol for stridency in the IPA, but a superscript ⟨ʢ⟩ (for a voiced epiglottal trill) is often used.[citation needed] In some literature, a subscript double tilde (≈) is sometimes used.