Noise control and acoustics

German noise law measures at the neighbour’s window, not at the machine: der Immissionsort is where the sound arrives, and der Immissionsrichtwert is the figure it is judged against. The small words around that figure carry a rule worth learning on this page. Unter and über take the dative when they say where a level stands, and the accusative when it crosses the line: der Pegel liegt unter dem Richtwert, but der Pegel sinkt unter den Richtwert; er bleibt über dem Richtwert, but er steigt über den Richtwert. It is the logic of a book lying on the table or being put on it, applied to a point on a scale. In a noise report the case therefore tells you something the verb only hints at: with the dative a problem exists or does not, with the accusative it has just appeared or just been solved.