frication

Frication is a term used in acoustics and phonetics to describe the noise produced by turbulence as air flows through a constriction or past a rough surface. In speech science, frication refers specifically to the friction noise that characterizes fricative consonants such as f, s, and ʃ. It results from turbulent eddies formed when the vocal tract constriction is narrow enough to disrupt the air stream, producing a continuous, hiss-like sound that can be sustained while the constriction remains.

Frication is distinct from other sources of speech noise. Aspiration is a transient noise that follows a plosive release, while voicing is the periodic vibration of the vocal folds. Frication can occur with voiceless fricatives (predominantly noisier) and with voiced fricatives, where the frication noise blends with vocal fold vibration. The spectral pattern of frication depends on place of articulation and constriction: sibilants produce concentrated high-frequency energy, whereas non-sibilants have more low-frequency energy and a softer hiss.

In analysis, frication is treated as a noise source in the speech signal. Researchers measure frication duration, intensity, and spectral slope to distinguish sounds and study language variation. Frication is also a consideration in speech technology, including recognition and synthesis, where accurate modeling of the noise component improves perceptual realism.

Outside linguistics, the term can describe friction-generated turbulence in airflow or machinery, but in linguistic contexts it specifically denotes the continuous turbulence-based noise associated with fricative articulation.