ANSI/ASA S1.13

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6.1.1.1 Steady continuous sound. Continuous sound whose sound pressure level remains essentially constant during the observation period. NOTE 1 A continuous sound may be considered steady if either its time-averaged A-weighted sound level over a one second integration period ("short-term time-averaged sound level" or "short-term Leq") or its A-weighted sound level measured with the slow exponential time weighting does not vary by more than ±3 dB about its mean level over the observation period. NOTE 2 Certain sounds that are characterized by "stepwise" variations in levels may also be considered steady provided that the level during each step meets the condition in Note 1 above when the observation period is equal to the duration of each stepwise variation (see also Sec. 9.4.1.1). NOTE 3 Examples of steady continuous sounds are the noise from fans and blowers, the hum of a transformer, and the noise inside a car or truck moving at constant speed over a uniform roadway. An example of a steady continuous sound that varies in a stepwise manner is that near a paint-drying area of a factory where first one air dryer is running, and then two, and then perhaps four, then back to one, etc. 6.1.1.2 Fluctuating continuous sound. Continuous sound whose sound pressure level varies significantly, but not in an impulsive manner, during the observation period. NOTE 1 A continuous sound may be considered fluctuating if either its time-averaged A-weighted sound level over a one second integration period ("short-term time-averaged sound level" or "short-term Leq") or its A-weighted sound level measured with the slow exponential time weighting varies by more than ±3 dB about its mean value over the observation period. NOTE 2 Examples of fluctuating continuous sounds are the noise from bulldozers and backhoes during grading operations; the sound of gusting wind rustling through leaves, or waves striking a beach; and the noise from a lawn mower traversing a neighbor's yard.