Aircraft have to meet noise limits on takeoff, on approach, and "sideline". The measuring point for takeoff is 6500 meters from the start of takeoff roll, on the runway centerline, and the stage 3 limit for a four-engine aircraft weighing 850,000 lb or more is 106 EPNdB, while the limit for a twin-engine weighing 300,000 lb would be 95 EPNdB. Seems to me if you don't quite meet one criterion you can make up for it by beating the other criteria with something to spare.
I guess somewhere in FAR 36 you'll find a definition of EPNdB that's about 200 times more detailed than you wanted; it's something about weighting the various frequencies so that an Effective Perceived Noise (?) Decibel is a better measure of how noisy something seems to the human ear.