| Definition: | a sound pressure level in decibels, obtained by adding to perceived noise level an adjustment that is related to the degree of irregularity that may occur among contiguous one-third-octave band sound pressure levels of an aircraft noise
NOTE 1 – The adjustment is described in ISO 3891-1978 ; it may vary from 0 dB to 6,7 dB.
NOTE 2 – The adjustment purports to account for the extra subjective noisiness caused by pronounced audible tones such as may be generated by propellors, compressors, turbines or fans.
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