acoustics, loudness is the
subjective perception of
sound pressure. More formally, it is defined as, "That attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud."
 The relation of physical attributes of sound to perceived loudness consists of physical, physiological and psychological components. The study of apparent loudness is included in the topic of
psychoacoustics and employs methods of
In different industries, loudness may have different meanings and different measurement standards. Some definitions, such as
ITU-R BS.1770 refer to relative loudness of different segments of electronically reproduced sounds, such as for broadcasting and cinema. Others, such as ISO 532A (Stevens loudness, measured in
sones), ISO 532B (
Zwicker loudness), DIN 45631 and ASA/ANSI S3.4, have a more general scope and are often used to characterize loudness of environmental noise.
Loudness, a subjective measure, often confused with physical measures of sound strength such as
sound pressure, sound pressure
sound intensity or
sound power. Filters such as
LKFS attempt to compensate measurements to correspond to loudness as perceived by the typical human.