Fricative

A fricative is a consonant produced with a narrow constriction that generates sustained turbulent airflow and its associated noise. The articulators approach closely without creating the complete oral closure of a plosive. Place of articulation and voicing further distinguish different fricatives.^[ref]

Sustain [f] and then [v]. Both use the lower lip and upper teeth, but the second normally adds vocal fold vibration. A spectrogram can display a noise component and, where present, periodic structure. The physical source of the noise is the constricted airflow, while the vocal tract shapes its spectrum. Merely calling a sound unvoiced does not identify it as a fricative.