|Manners of articulation|
Trills are very different from flaps. Whereas with a flap (or tap), a specific gesture is used to strike the active articulator against the passive one, in the case of a trill the articulator is held in place, where the airstream causes it to vibrate. Usually a trill vibrates for 2–3 periods, but may be up to 5, or even more if geminate. However, trills may also be produced with only a single period. While this might seem like a flap, the articulation is different; trills will vary in the number of periods, but flaps do not.
Trill consonants included in the International Phonetic Alphabet:
The bilabial trill is uncommon. The coronal trill is most frequently alveolar [r͇], but dental and postalveolar articulations [r̪] and [r̠] also occur. An alleged retroflex trill found in Toda has been transcribed [ɽ] (that is, the same as the retroflex flap), but might be less ambiguously written [ɽ͡r], as only the onset is retroflex, with the actual trill being alveolar. One other trill has been reported as a consonant, an epiglottal trill. Epiglottal consonants are often allophonically trilled,  and in some languages the trill is the primary realization of the consonant. There is no official symbol for this in the IPA, but occasionally [я] has been used in the literature. There are also so-called strident vowels which are accompanied by epiglottal trill.
The cells in the IPA chart for the velar and pharyngeal places of articulation are shaded. A velar trill is impossible because the middle of the tongue and walls of the throat are insufficiently flexible to vibrate in such a manner. A palatal trill is impractically difficult, if not actually impossible. The glottis quite readily vibrates, but this occurs as the phonation of vowels and consonants, not as a consonant of its own.
The Czech language has two contrastive alveolar trills, one a fricative trill (written ř in the orthography). In the fricative trill the tongue is raised, so that there is audible frication during the trill, sounding rather like a simultaneous [r] and [ʐ]. A symbol for this sound, [ɼ], has been dropped from the IPA, and it is now generally transcribed as a raised r, [r̝].
Snoring typically consists of vibration of the uvula and the soft palate (velum). While the former part is simply a uvular trill, there is no standard linguistic term for the latter. It does not constitute a velar trill, because the velum is here the active articulator, not the passive; the tongue is not involved at all. (The Extensions to the IPA identify a fricative pronounced with this same configuration as velopharyngeal.)
- listen (epiglottal fricative)
- Ladefoged, Peter; Maddieson, Ian (1996). The Sounds of the World's Languages. Oxford: Blackwell. ISBN 0-631-19814-8.