Weighting

The process offrequency weightinginvolves emphasizing the contribution of particular aspects of a phenomenon (or of a set ofdata) over others to an outcome or result; thereby highlighting those aspects in comparison to others in theanalysis.That is, rather than each variable in the data set contributing equally to the final result, some of the data is adjusted to make a greater contribution than others. This is analogous to the practice of adding (extra)weightto one side of a pair of scales in order to favour either the buyer or seller.

While weighting may be applied to a set of data, such as epidemiological data, it is more commonly applied to measurements of light, heat, sound,gamma radiation,and in fact any stimulus that is spread over aspectrumof frequencies.

Weighting in acoustics

Weighting and loudness

In the measurement ofloudness,for example, aweighting filteris commonly used to emphasise frequencies around 3 to 6 kHz where the human ear is most sensitive, while attenuating very high and very low frequencies to which the ear is insensitive. A commonly used weighting is theA-weightingcurve, which results in units of dBA sound pressure level. Because the frequency response of human hearing varies with loudness, the A-weighting curve is correct only at a level of 40-phonand other curves known asB-,C-andD-weightingare also used, the latter being particularly intended for the measurement of aircraft noise.

Weighting in audio measurement

In broadcasting and audio equipment measurements468-weightingis the preferred weighting to use because it was specifically devised to allow subjectively valid measurements on noise, rather than pure tones. It is often not realised that equal loudness curves, and hence A-weighting, really apply only to tones, as tests withnoise bandsshow increased sensitivity in the 5 to 7 kHz region on noise compared to tones.

Otherweighting curvesare used inrumble measurementandflutter measurementto properly assess subjective effect.

In each field of 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 thephon(1kHzequivalent level).

In the fields of acoustics and audio engineering, it is common to use a standard curve referred to asA-weighting,one of a set that are said to be derived fromequal-loudness contours.

Application to hearing in aquatic animals

Auditory frequency weighting functions for marine mammals were introduced by Southall et al. (2007).^[1]

Weighting in electromagnetism

Weighting and gamma rays

In the measurement of gamma rays or other ionising radiation, a radiation monitor or dosimeter will commonly use a filter to attenuate those energy levels or wavelengths that cause the least damage to the human body but letting through those that do the most damage, so any source of radiation may be measured in terms of its true danger rather than just its strength. The resulting unit is thesievertor microsievert.

Weighting and television colour components

Another use of weighting is in television, in which the red, green and blue components of the signal are weighted according to their perceived brightness. This ensures compatibility with black and white receivers and also benefits noise performance and allows separation into meaningfulluminanceandchrominancesignals for transmission.

Weighting and UV factor derivation for sun exposure

Skin damage due to sun exposure is very wavelength dependent over the UV range 295 to 325 nm, with power at the shorter wavelength causing around 30 times as much damage as the longer one. In the calculation ofUV Index,a weighting curve is used which is known as the McKinlay-Diffey Erythema action spectrum.[1]Archived2010-06-13 at theWayback Machine

References

^Marine Mammal Noise Exposure Criteria: Initial Scientific Recommendations. Brandon L. Southall, Ann E. Bowles, William T. Ellison, James J. Finneran, Roger L. Gentry, Charles R. Greene Jr., David Kastak, Darlene R. Ketten, James H. Miller, Paul E. Nachtigall, W. John Richardson, Jeanette A. Thomas, & Peter L. Tyack. Aquatic Mammals

External links

[1] Marine Mammal Noise Exposure Criteria: Initial Scientific Recommendations. Brandon L. Southall, Ann E. Bowles, William T. Ellison, James J. Finneran, Roger L. Gentry, Charles R. Greene Jr., David Kastak, Darlene R. Ketten, James H. Miller, Paul E. Nachtigall, W. John Richardson, Jeanette A. Thomas, & Peter L. Tyack. Aquatic Mammals

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