A fricative is a consonant produced by forcing air through a narrow channel made by placing two articulators close together.
All sibilants are coronal, but may be dental, alveolar, postalveolar, or palatal (retroflex) within that range.
Prototypical retroflexes are subapical and palatal, but they are usually written with the same symbol as the apical postalveolars.
The alveolars and dentals may also be either apical or laminal, but this difference is indicated with diacritics rather than with separate symbols.
[5] The lateral fricative occurs as the ll of Welsh, as in Lloyd, Llewelyn, and Machynlleth ([maˈxənɬɛθ], a town), as the unvoiced 'hl' and voiced 'dl' or 'dhl' in the several languages of Southern Africa (such as Xhosa and Zulu), and in Mongolian.
[8] Until its extinction, Ubykh may have been the language with the most fricatives (29 not including /h/), some of which did not have dedicated symbols or diacritics in the IPA.
Voicing contrasts in fricatives are largely confined to Europe, Africa, and Western Asia.
[11] This phenomenon occurs because voiced fricatives have developed from lenition of plosives or fortition of approximants.
(Relatedly, several languages have the voiced affricate [dʒ] but lack [tʃ], and vice versa.)
Fricatives appear in waveforms as somewhat random noise caused by the turbulent airflow, upon which a periodic pattern is overlaid if voiced.
[13] The centre of gravity (CoG), i.e. the average frequency in a spectrum weighted by the amplitude (also known as spectral mean), may be used to determine the place of articulation of a fricative relative to that of another.