The perceived noise level is a single number rating of aircraft noise@ based upon objective acoustic measurements@ which is related to the relative subjective response to aircraft noise The perceived noise level@ as defined in this standard@ is based only on the noise spectra measured in the eight octave or 24 one-third octave frequency bands within the nominal range of 50 to 10@000 Hz. As such@ it is considered an accurate method for rating the noisiness of broadbandjet aircraft type sounds of similar timeduration which do not contain strong discrete frequency components For rating the loudness of certain classed of noise (i.e.@ steady state)@ another procedure@ defined in Ref. 1@ and not unlike that specified herein@ is also available. However@ the measure@ perceived noisiness@ has become generally accepted for defining the noisiness ofjet aircraft When the additional effects of duration of the time-varying aircraft noise signal and the presence of discrete frequency components are to be taken into account@ the effective perceived noise level (EPNL)@ as defined in Refs. 2@3@ and 4@ is the preferred measure