A-weighting is the most commonly used of a family of curves defined in the International standard IEC61672:2003 and various national standards relating to the measurement of sound level, as opposed to actual sound intensity. The others are B, C, D and now Z weightings (see below). Sound level, loudness and sound intensity are not the same things; indeed there isn't even a simple relationship between them, because the human hearing system is more sensitive to some frequencies than others, and fu… (More on A-weighting)