A special filter used in measuring loudness levels, and consequently carried over into audio noise measurements of equipment. The filter design “weights” or gives more attention to certain frequency bands than others. The goal is to obtain measurements that correlate well with the subjective perception of noise. (Technically termed psophometric (pronounced “so-fo-metric”) filters, after the psophometer, a device used to measure noise in telephone circuits, broadcast, and other audio communication equipment. A psophometer was a voltmeter with a set of weighting filters.) Weighting filters are a special type of band-limiting filters designed to correspond to the way we hear or some other specific criteria.