‘De-essing’ is the classic compressor technique used to address vocal sibilance through processing.
It isn’t really practical or productive to address micro-muscular vocal technique during a session, so your best bet to mitigate sibilance at the source is microphone selection and placement. This pressurization causes some amount of noise that forms the consonant sounds we would recognize from a phase like, “Sally sits sideways on the tennis trolley.” Sibilance is a very necessary feature of human speech, but when there’s (subjectively) too much noise created during these consonants, we get a very distracting harshness. During these sorts of utterances, the airway (usually the mouth) is drastically constricted by two anatomical features, like the teeth, tongue, or palette. In phonetic terms, sibilance comes from a type of vocal formant called a fricative consonant. Sibilance at the Source (best read with sibilant whistle) This article will discuss some ways to control vocal sibilance, and keep the problem from becoming a musical distraction. This problem is usually caused by the actual vocal formant, but can also be exaggerated by microphone placement and technique. Sibilance is often centered between 5kHz to 8kHz, but can occur well above that frequency range. Vocal sibilance is an unpleasant tonal harshness that can happen during consonant syllables (like S, T, and Z), caused by disproportionate audio dynamics in upper midrange frequencies.
