Effective perceived noise in decibels (EPNdB) or Effective Perceived Noise Level (EPNL) is a measure of the relative noisiness of an individual aircraft pass-by event.
[3] The scaling is such that the EPNdB rating represents the integrated noisiness over a ten-second period; EPNdB of 100 dB means that the event has the same integrated noisiness as a 100 PNdB sound lasting ten seconds.
In Australia and Canada, it's the basis for the ANEF and NEF noise exposure forecast used in place of the DNL and Day-evening-night metrics used in the US and Europe respectively.
Detailed information on measurement of aircraft acoustic signature to meet the requirements of Annex 16 is found in ICAO Document 9501[6] and IEC 61265.
The individual band sound pressure levels are converted to "noy" values[8] which are then summed in the manner of Stevens' MKVI loudness to yield a total noy value.