Can a speech vibration be random?
Certainly. When structures above the larynx are involved in setting the airstream into vibration, these vibrations are characterised as aperiodic, or random. The two main types of random vibration are turbulence and transience. We associate turbulence with the class of sounds known as the fricatives. When the airstream from the lungs moves rapidly through a narrow constriction in the vocal tract appropriate for a fricative, it becomes turbulent. Turbulence is a series of random vibrations. These random vibrations can additionally strike an object in their path (such as the teeth) and will set whatever air is in front of them into vibration. Transience is a form of random vibration normally associated with the class of sounds called stops or plosives. Because stops are made with a complete closure somewhere in the vocal tract, the release of this closure is associated with an audible burst of sound because pressure has built up behind the closure. This audible burst is sharp and short (
