Soundproofing glossary definition of A-weighted sound pressure level

A-weighted sound pressure level :

Ten times the logarithm of the ratio of A-weighted squared sound pressure to the squared reference sound pressure of 20 micropascal, the squared sound pressure being obtained with fast (F) (125-ms) exponentially weighted time averaging. Alternatively slow (S) (1000-ms) exponentially weighted time averaging may be specified. Unit, decibel (dB); symbol, L _A.