The sj-sound ( ) is a voiceless fricative phoneme found in the sound system of most dialects of Swedish. It has a variety of realisations, whose precise phonetic characterisations are a matter of debate, but which often feature distinct labialization. The sound is represented in Swedish orthography by a number of spellings, the most common of which are (from which the common Swedish name for the sound is derived), , , and (before front vowels) ; if considered in complementary distribution with , up to 65 different spellings for the phoneme have been identified in native words and loanwords. The sound should not be confused with the Swedish tj-sound , usually spelled , , or (before front vowels) .
The IPA letter for these sounds, (called Hooktop heng in the IPA Handbook), has occasionally been used for other languages, but as it has no set phonetic value, this is only useful as an abstraction (as indeed it is in Swedish).
The sj-sounds are transcribed in the International Phonetic Alphabet. The International Phonetic Association (IPA) describes as "simultaneous and " (that is, ). Other descriptive labels include:
However, neither of these realizations are attested, and phoneticians doubt that such a realization is possible in "ordinary language," as it is difficult to produce, or even to hear, turbulent (fricative) airflow at two places of articulation simultaneously.
The closest sound found in English, as well as many other languages, is the voiceless postalveolar fricative (Swedish words with the sound often correspond to English words with "sh", such as "shield", "shoot", from earlier Proto-Germanic *sk), although usually the closest audible approximation is the voiceless labialized velar approximant found in some English dialects. Regionally, it varies from being more -like in the standard speech, to being more -like in northern Sweden and Finland. The tj-sound (which often corresponds to English words with "ch", such as "chicken", "church") remains distinct, varying from more -like (i.e., ) in the standard speech to more -like in northern Sweden and Finland.
The place of articulation of the sj-sound varies over Swedish regions and is not agreed upon. It has been variously found to be the following:
Consider the following comments by Peter Ladefoged and Ian Maddieson:
A sound transcribed with is also reported to occur in the Colognian dialect of Ripuarian in Germany, being articulated in positions in words that enveloping Standard German has .
The acoustic difference between and the Kölsch is difficult to perceive but the articulation is clearly distinct. A similarity between Swedish and the Kölsch has not been established, and comments suggest that the choice of might well have been based upon a misunderstanding. Certainly, the Kölsch is not doubly articulated and even contrasts with a slightly velarized .
Some phoneticians, such as of the University of Cologne in his lessons on IPA transcription, suggest that might be a better symbol for the sound.
A sound transcribed with is also reported word-initially and word-medially in the Wutun language, where it is described simply as a "velar glide", which would be . The symbol has also been used for an allophone of that occurs before in some accents of the Bahing language of Nepal.