equivalent continuous sound level (Leq)
For rapidly changing noise levels, the averaging level is used as an aid and is usually referred to as "equivalent continuous sound level" (Leq) or "time-averaged sound level"( LAT).
The most common term used is LAeqT. This sound level is defined as twenty times the logarithm to base 10 of the sound level ratio between the rms value of the sound pressure during a given time interval and the reference sound pressure. Sound pressure is determined at a standard frequency and is expressed in decibels( dB).
Since the sound pressure level is an average level, the Leq value can rise and fall. However, the more it is measured, the more stable it becomes, since it accumulates all the noise from the beginning of the measurement.