Pick a noise source at a home’s window at night, and read how the three governing instruments rate it — and whether they can register it at all. Levels are the sound at the nearest façade, in A-weighted decibels.
How to read it. The WHO values are health-based recommendations, not law. The European directive maps and plans but sets no limit to breach. Spain’s binding decree works in A-weighted decibels too, but adds correction terms for a tonal or low-frequency character — the +Kt and +Kf — which is why it alone can catch a hum that sits, on the plain meter, below the limit. Assessed against the residential night quality objective of 55 dB; a source-specific emitter limit can be stricter still.