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Loudness, a subjective measure, is often confused with physical measures of sound strength such as sound pressure, sound pressure level (in decibels), sound intensity or sound power. Weighting filters such as A-weighting and LKFS attempt to compensate measurements to correspond to loudness as perceived by the typical human.
I is the sound intensity; I 0 is the reference sound intensity; 1 Np = 1 is the neper; 1 B = 1 / 2 ln(10) is the bel; 1 dB = 1 / 20 ln(10) is the decibel. The commonly used reference sound intensity in air is [5] = /. being approximately the lowest sound intensity hearable by an undamaged human ear under room conditions.
It is well established that human hearing is more sensitive to some frequencies than others, as demonstrated by equal-loudness contours, but it is not well appreciated that these contours vary depending on the type of sound. The measured curves for pure tones, for instance, are different from those for random noise.
Analysis of sound and acoustics plays a role in such engineering tasks as product design, production test, machine performance, and process control. For instance, product design can require modification of sound level or noise for compliance with standards from ANSI, IEC, and ISO. The work might also involve design fine-tuning to meet market ...
Quantity Unit Remarks Name Symbol Definition Name Symbol period, periodic time: T: time of one cycle: second: s: frequency: f, ν: f = 1/T: hertz: Hz: 1 Hz = 1 s −1: loudness level: L N: L N = ln(p eff /p 0) 1 kHz where p eff is the root-mean-square value of the sound pressure of a pure tone of 1 kHz, which is judged by a normal observer under standardized listening conditions as being as ...
[28] [29] [30] This means that at short durations, a very short sound can sound softer than a longer sound even though they are presented at the same intensity level. Past around 200 ms this is no longer the case and the duration of the sound no longer affects the apparent loudness of the sound.
An equal-loudness contour is a measure of sound pressure level, over the frequency spectrum, for which a listener perceives a constant loudness when presented with pure steady tones. [1] The unit of measurement for loudness levels is the phon and is arrived at by reference to equal-loudness contours.
Loudness level measured with K frequency weighting. R 128 target level is: L K = −23 LUFS: LUFS: Loudness Units referenced to full scale Loudness measurement unit on an absolute scale, K-weighted, [3] relative to a digital scale (the upper limit of which is 0 dBFS). Equivalent with LKFS, used in ITU-R BS.1770.