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Loudness is the characteristic of a sound that is primarily a psychological correlate of physical strength (amplitude). 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".〔American National Standards Institute, "American national psychoacoustical terminology" S3.20, 1973, American Standards Association.〕 Loudness, a subjective measure, is often confused with objective measures of sound strength such as sound pressure, sound pressure level (in decibels), sound intensity or sound power. Filters such as A-weighting attempt to adjust sound measurements to correspond to loudness as perceived by the typical human. However, loudness perception is a much more complex process than A-weighting.〔 Loudness is also affected by parameters other than sound pressure, including frequency, bandwidth and duration. == Explanation == The perception of loudness is related to both the sound pressure level (SPL) and duration of a sound. The human auditory system averages the effects of SPL over a 600–1000 ms interval. A sound of constant SPL will be perceived to increase in loudness as samples of duration 20, 50, 100, 200 ms are heard, up to a duration of about 1 second at which point the perception of loudness will stabilize. For sounds of duration greater than 1 second, the moment-by-moment perception of loudness will be related to the average loudness during the preceding 600–1000 ms. For sounds having a duration longer than 1 second, the relationship between SPL and loudness can be approximated by a power function in which SPL has an exponent of 0.6, while that between SPL and intensity can be approximated by a power function with an exponent of 0.3 (Stevens' power law). More precise measurements indicate that loudness increases with a higher exponent at low and high levels and with a lower exponent at moderate levels. Units used to measure loudness: *Sone (loudness ''N'') *Phon (loudness level ''L'') The sensitivity of the human ear changes as a function of frequency, as shown in the equal-loudness graph. Each line on this graph shows the SPL required for frequencies to be perceived as equally loud. It also shows that humans with good hearing are most sensitive to sounds around 2–4 kHz, with sensitivity declining to either side of this region. A complete model of the perception of loudness will include the integration of SPL by frequency and the duration of each.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Loudness」の詳細全文を読む スポンサード リンク
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