Which type of noise is characterized by variability in presence and intensity?

Intermittent noise is defined by fluctuations in its presence and intensity, meaning that it does not occur at a constant level. This type of noise can burst in and out, varying significantly in its loudness and duration of occurrence. Such variations can be caused by machinery that operates in cycles or situations where noise is generated sporadically, resulting in an unpredictable auditory environment.

In contrast, continuous noise is more uniform, maintaining a steady level over time. Steady state noise is similar in that it also remains constant, providing a constant auditory signal that lacks variability. Impulse noise, on the other hand, refers to short bursts of noise—such as a gunshot or hammer strike—that occur instantaneously rather than over a sustained period. This distinguishes impulse noise from intermittent noise, which has a more cyclical presence. Therefore, intermittent noise effectively describes sound that varies in both intensity and occurrence, making it the correct answer.