Hissing

Hissing is a sharp, sibilant sound produced when a stream of air passes through a narrow opening or contact point, causing the airstream to become turbulent and generate high-frequency sound energy. The noise is dominated by frication—the friction of air against a small constriction—and its spectral content is typically rich in higher frequencies, giving it a characteristic hiss.

In human speech, hissing commonly corresponds to the voiceless alveolar sibilant /s/ and related sounds, produced by directing air along the tongue toward the teeth. Hissing can also occur unintentionally when air leaks through gaps in the mouth or lips. The word “hiss” is widely used as onomatopoeia in writing to represent this sound or to convey disapproval or warning.

Nonhuman hissing is most familiar in snakes, which emit a hiss by forcing air through the glottis while expanding the mouth and sometimes raking the teeth. The hiss serves as a defensive display. Similar air-friction noises occur in other animals and in mechanical systems when steam, air, or gas escapes through a small opening.

In everyday contexts, hissing appears in recordings and audio equipment as a background noise sometimes referred to as hiss (for example, tape hiss or vinyl hiss). It is also produced by vents, pipes, and other sources of escaping air, especially when airflow is restricted or turbulent.