Sibilant

Sibilants are fricative and affricate consonants of higher amplitude and pitch, made by directing a stream of air with the tongue towards the teeth. Examples of sibilants are the consonants at the beginning of the English words sip, zip, ship, and genre. The symbols in the International Phonetic Alphabet used to denote the sibilant sounds in these words are, respectively,. Sibilants have a characteristically intense sound, which accounts for their paralinguistic use in getting one's attention.

Overview

A broader category is stridents, which include more fricatives than sibilants such as uvulars. Sibilants are a higher pitched subset of the stridents. The English sibilants are:

Fricatives
Affricates /tʃ, dʒ/

while the English stridents are:

as and are stridents but not sibilants because they are lower in pitch.
Some linguistics use the terms "stridents" and "sibilants" interchangeably to refer to the greater amplitude and pitch compared to other fricatives.
"Stridency" refers to the perceptual intensity of the sound of a sibilant consonant, or obstacle fricatives or affricates, which refers to the critical role of the teeth in producing the sound as an obstacle to the airstream. Non-sibilant fricatives and affricates produce their characteristic sound directly with the tongue or lips etc. and the place of contact in the mouth, without secondary involvement of the teeth.
The characteristic intensity of sibilants means that small variations in tongue shape and position are perceivable, with the result that there are many sibilant types that contrast in various languages.

Acoustics

Sibilants are louder than their non-sibilant counterparts, and most of their acoustic energy occurs at higher frequencies than non-sibilant fricatives—usually around 8,000 Hz.

Sibilant types

All sibilants are coronal consonants. However, there is a great deal of variety among sibilants as to tongue shape, point of contact on the tongue, and point of contact on the upper side of the mouth.
The following variables affect sibilant sound quality, and, along with their possible values, are ordered from sharpest to dullest :

Tongue shape:, alveolo-palatal, palato-alveolar, retroflex
Place of articulation : or denti-alveolar,, postalveolar,
Point of contact on the tongue: "closed", non-"closed",,

Generally, the values of the different variables co-occur so as to produce an overall sharper or duller sound. For example, a laminal denti-alveolar grooved sibilant occurs in Polish, and a subapical palatal retroflex sibilant occurs in Toda.

Tongue shape

The main distinction is the shape of the tongue. The following tongue shapes are described, from sharpest and highest-pitched to dullest and lowest-pitched:

Grooved : This groove accepts a large volume of air that is forced through a typically narrow aperture that directs a high-velocity jet of air against the teeth, which results in a high-pitched, piercing "hissing" sound. Because of the prominence of these sounds, they are the most common and most stable of sibilants cross-linguistically. They occur in English, where they are denoted with a letter s or z, as in soon or zone.
Alveolo-palatal : with a convex, V-shaped tongue, and highly palatalized.
Palato-alveolar : with a "domed" tongue. These sounds occur in English, where they are denoted with letter combinations such as sh, ch, g, j or si, as in shin, chin, gin and vision. Sometimes have be referred to as "lamino-postalveolar" or "lamino-prepalatal".
Retroflex : with a flat or concave tongue, and no palatalization. There is a variety of these sounds, some of which also go by other names. The or "true" retroflex sounds are the very dullest and lowest-pitched of all the sibilants.

The latter three post-alveolar types of sounds are often known as "hushing" sounds because of their quality, as opposed to the "hissing" alveolar sounds. The alveolar sounds in fact occur in several varieties, in addition to the normal sound of English s:

Palatalized: Sibilants can occur with or without raising the tongue body to the palate. Palatalized alveolars are transcribed e.g. and occur in Russian; they sound similar to the cluster occurring in the middle of the English phrase miss you.
Lisping: Alveolar sibilants made with the tip of the tongue near the upper teeth have a softer sound reminiscent of the "lisping" sound of English think. These sounds are relatively uncommon, but occur in some of the indigenous languages of California as well as in the Spanish dialects of western and southern Andalusia, mostly in the provinces of Cádiz, Málaga, Sevilla and Huelva. In these dialects, the lisping sibilant is the most common pronunciation of the letters s and z, as well as c before i or e, replacing the or that occur elsewhere in the country.

Speaking non-technically, the retroflex consonant sounds somewhat like a mixture between the regular English of "ship" and a strong American "r"; while the alveolo-palatal consonant sounds somewhat like a mixture of English of "ship" and the in the middle of "miss you".

Place of articulation

Sibilants can be made at any articulation, i.e. the tongue can contact the upper side of the mouth anywhere from the upper teeth to the hard palate, with the in-between articulations being denti-alveolar, and postalveolar.

Point of contact on the tongue

The tongue can contact the upper side of the mouth with the very tip of the tongue ; with the surface just behind the tip, called the blade of the tongue ; or with the underside of the tip. Apical and subapical articulations are always tongue-up, with the tip of the tongue above the teeth, while laminal articulations can be either tongue-up or tongue-down, with the tip of the tongue behind the lower teeth. This distinction is particularly important for retroflex sibilants, because all three varieties can occur, with noticeably different sound qualities.
For tongue-down laminal articulations, an additional distinction can be made depending on where exactly behind the lower teeth the tongue tip is placed. A little ways back from the lower teeth is a hollow area in the lower surface of the mouth. When the tongue tip rests in this hollow area, there is an empty space below the tongue, which results in a relatively duller sound. When the tip of the tongue rests against the lower teeth, there is no sublingual cavity, resulting in a sharper sound. Usually, the position of the tip of the tongue correlates with the grooved vs. hushing tongue shape so as to maximize the differences. However, the palato-alveolar sibilants in the Northwest Caucasian languages such as Ubykh are an exception. These sounds have the tongue tip resting directly against the lower teeth, which gives the sounds a quality that Catford describes as "hissing-hushing". Ladefoged and Maddieson term this a "closed laminal postalveolar" articulation, and transcribe them as, although this is not an IPA notation.

Symbols in the IPA

The following table shows the types of sibilant fricatives defined in the International Phonetic Alphabet:
Diacritics can be used for finer detail. For example, apical and laminal alveolars can be specified as vs ; a dental sibilant as ; a palatalized alveolar as ; and a generic "retracted sibilant" as, a transcription frequently used for the sharper-quality types of retroflex consonants. There is no diacritic to denote the laminal "closed" articulation of palato-alveolars in the Northwest Caucasian languages, but they are sometimes provisionally transcribed as.

Possible combinations

The attested possibilities, with exemplar languages, are as follows. Note that the IPA diacritics are simplified; some articulations would require two diacritics to be fully specified, but only one is used in order to keep the results legible without the need for OpenType IPA fonts. Also, Ladefoged has resurrected an obsolete IPA symbol, the under dot, to indicate apical postalveolar, and that notation is used here.

IPA	Tongue shape	Place of articulation	Place of articulation	Exemplifying languages
	hollow			southeast European Spanish s/z, Kumeyaay
	hollow			Polish s, z; Basque z, tz
	hollow			northern peninsular Spanish s; Basque s, ts; Mandarin s, z, c
	hollow		apical or laminal	English s, z ; American or southwest European Spanish s/z
	hollow		laminal	Toda, Ubykh, Abkhaz
	domed		apical or laminal	English sh, ch, j, zh and French ch, j
	domed			Toda; Basque x, tx
	palatalized			Mandarin x, j, q; Polish ś, ć, ź, dź; Ubykh; Abkhaz
	hollow			Ubykh; Abkhaz
,	hollow or flat			Polish sz, cz, ż, dż ; Mandarin sh, zh, ch
, etc.	hollow			Ubykh; Abkhaz; Kumeyaay; Toda; Russian
	curled			Toda

is an ad-hoc transcription. The old IPA letters are also available.
These sounds are usually just transcribed . Apical postalveolar and subapical palatal sibilants do not contrast in any language, but if necessary, apical postalveolars can be transcribed with an apical diacritic, as or . Ladefoged resurrects the old retroflex sub-dot for apical retroflexes, Also seen in the literature on e.g. Hindi and Norwegian is – the domed articulation of precludes a subapical realization.