Voiceless dental fricative

The voiceless dental non-sibilant fricative is a type of consonantal sound used in some spoken languages. It is familiar to most English speakers as the 'th' in think. Though rather rare as a phoneme among the world's languages, it is encountered in some of the most widespread and influential ones. The symbol in the International Phonetic Alphabet that represents this sound is ⟨θ⟩, and the equivalent X-SAMPA symbol is. The IPA symbol is the lowercase Greek letter theta, which is used for this sound in post-classical Greek, and the sound is thus often referred to as "theta".

The dental non-sibilant fricatives are often called "interdental" because they are often produced with the tongue between the upper and lower teeth, and not just against the back of the upper or lower teeth, as they are with other dental consonants.

This sound and its voiced counterpart are rare phonemes, occurring in 4% of languages in a phonological analysis of 2,155 languages. Among the more than 60 languages with over 10 million speakers, only English, northern varieties of the Berber languages of North Africa, Standard Peninsular Spanish, various dialects of Arabic, Swahili (in words derived from Arabic), and Greek have the voiceless dental non-sibilant fricative. Speakers of languages and dialects without the sound sometimes have difficulty producing or distinguishing it from similar sounds, especially if they have had no chance to acquire it in childhood, and typically replace it with a voiceless alveolar fricative (as in Indonesian), voiceless dental stop, or a voiceless labiodental fricative ; known respectively as th-alveolarization, th-stopping, and th-fronting.

The sound is known to have disappeared from a number of languages, e.g. from most of the Germanic languages or dialects, where it is retained only in Scots, English, and Icelandic, but it is alveolar in the last of these. Among non-Germanic Indo-European languages as a whole, the sound was also once much more widespread, but is today preserved in a few languages including the Brythonic languages, Peninsular Spanish, Galician, Venetian, Tuscan, Albanian, some Occitan dialects and Greek. It has likewise disappeared from many modern varieties of Arabic (excluding Tunisian, Mesopotamian Arabic and various dialects in the Arabian Peninsula, as well as Modern Standard Arabic).

Features
Features of the voiceless dental non-sibilant fricative:

It does not have the grooved tongue and directed airflow, or the high frequencies, of a sibilant.

Voiceless denti-alveolar sibilant
The voiceless denti-alveolar sibilant is the only sibilant fricative in some dialects of Andalusian Spanish. It has no official symbol in the International Phonetic Alphabet, though its features would be transcribed ⟨s̻̪⟩ or ⟨s̪̻⟩ (using the ⟨◌̻⟩, the diacritic marking a laminal consonant, and ⟨◌̪⟩, the diacritic marking a dental consonant). It is usually represented by an ad-hoc symbol such as ⟨s̄⟩, ⟨θˢ̣⟩, or ⟨s&#799;⟩ (advanced diacritic).

describes this sound as follows: " is a voiceless, corono-dentoalveolar groove fricative, the so-called s coronal or s plana because of the relatively flat shape of the tongue body.... To this writer, the coronal, heard throughout Andalusia, should be characterized by such terms as "soft," "fuzzy," or "imprecise," which, as we shall see, brings it quite close to one variety of ... Canfield has referred, quite correctly, in our opinion, to this  as "the lisping coronal-dental," and Amado Alonso remarks how close it is to the post-dental , suggesting a combined symbol  to represent it".

Features
Features of the voiceless denti-alveolar sibilant:


 * Its place of articulation is denti-alveolar, which means it is articulated with a flat tongue against the alveolar ridge and upper teeth.
 * It is normally laminal, which means it is pronounced with the blade of the tongue.