High Quality Content by WIKIPEDIA articles! A weighting filter is used to emphasise or suppress some aspects of a phenomenon compared to others, for measurement or other purposes. In each field of audio measurement, special units are used to indicate a weighted measurement as opposed to a basic physical measurement of energy level. For sound, the unit is the phon. In the measurement of loudness, for example, an A-weighting filter is commonly used to emphasize frequencies around 3 6 kHz where the human ear is most sensitive, while attenuating very high and very low frequencies to which the ear is insensitive.