Vowel duration is an important cue for voicing of syllable final stops. Many of the same acoustic cues to voicing contrasts apply to fricatives and affricatives. The essential articulatory feature of a fricative is a narrow constriction maintained somewhere in the vocal tract. When air passes through the constriction at a suitable rate of flow, a condition called turbulence results. Compared with stops and affricatives, fricatives have the longest noise segments.
Formant transitions can play a secondary role in improving fricative recognition.
The overall noise energy of the nonstridents is less than that for the stridents. As a group the non-stridents are weak in overall energy and posses a fairly flat diffuse spectra. Formant transition is more effective than the noise segment as a cue for perception of the nonstridents. A complex sound, involving a sequence of stop and fricative articulation. The frication for affricates tends to be shorter than that for fricatives For the syllable initial position, the primary acoustic cues that distinguish affricates from stops appear to be the rise time of the noise energy and the duration of frication.