| Definition: | logarithm of the ratio of a given sound pressure to the reference sound pressure of 20 μPa, the sound pressure being obtained with a standard frequency weighting and with a standard exponential time weighting. Sound level in decibels is twenty times the logarithm to the base ten of that ratio
NOTE 1 – Standard frequency weightings A, В and C and standard exponential time weightings fast (F), slow (S) and impulse (I) are given in IEC 651 (1979): Sound level meters.
NOTE 2 – Time and frequency weightings employed should be specified, but if not stated explicitly, fast (F) exponential time weighting and A-frequency weighting are understood.
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