exceeded, maximum, and minimum sound level
The sound level exceeded during a given percentage of a measurement period is the percentile-exceeded sound level (Lx). Examples include L10, L50, and L90. L10 is the A-weighted sound level that is exceeded 10 percent of the measurement period, L50 is the level exceeded 50 percent of the period, and so on. L50 is the median sound level measured during the measurement period. L90, the sound level exceeded 90 percent of the time, excludes high localized sound levels produced by nearby sources such as single car passages or bird chirps. L90 is often used to represent the background sound level. L50 is also used to provide a less conservative assessment of the background sound level.
The maximum sound level (Lmax) and the minimum sound level (Lmin) are the maximum and minimum sound levels respectively, measured during the measurement period. When a sound meter is set to the "slow" response setting as is typical for most community noise measurements, the Lmax and Lmin values are the maximum and minimum levels measured over a one-second period.