High Quality Content by WIKIPEDIA articles! The voiceless alveolar fricatives are consonantal sounds. The symbol in the International Phonetic Alphabet that represents these sounds depends on whether a sibilant or non-sibilant fricative is being described. The symbol for the alveolar sibilant is s, and the equivalent X-SAMPA symbol is s. The IPA symbol [s] is not normally used for dental or postalveolar sibilants unless modified by a diacritic ([s?] and [s?] respectively). The IPA symbol for the alveolar non-sibilant fricative is derived by means of diacritics; it can be ?? or ???, or it can be [??], using the alveolar diacritic from the Extended IPA.