The process of frequency weighting involves emphasizing the contribution of particular aspects of a phenomenon (or of a set of

data Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...

) over others to an outcome or result; thereby highlighting those aspects in comparison to others in the

analysis Analysis (: analyses) is the process of breaking a complex topic or substance into smaller parts in order to gain a better understanding of it. The technique has been applied in the study of mathematics and logic since before Aristotle (38 ...

. 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)

weight In science and engineering, the weight of an object is a quantity associated with the gravitational force exerted on the object by other objects in its environment, although there is some variation and debate as to the exact definition. Some sta ...

to 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 A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

, and in fact any stimulus that is spread over a

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

of frequencies.

Weighting in acoustics

Weighting and loudness

In the measurement of

loudness In acoustics, loudness is the subjectivity, subjective perception of sound pressure. More formally, it is defined as the "attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud". The relat ...

, for example, a

weighting filter A weighting filter is used to emphasize or suppress some aspects of a phenomenon compared to others, for measurement or other purposes. Audio applications In each field of audio measurement, special units are used to indicate a weighted measure ...

is 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 the

A-weighting A-weighting is a form of frequency weighting and the most commonly used of a family of curves defined in the International standard IEC 61672:2003 and various national standards relating to the measurement of sound pressure level. A-weighti ...

curve, 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-

phon The phon is a logarithmic unit of loudness level for tones and complex sounds. Loudness is measured in sones, a linear unit. Human sensitivity to sound is variable across different frequencies; therefore, although two different tones may pres ...

and other curves known as B-, C- and D-weighting are also used, the latter being particularly intended for the measurement of aircraft noise.

Weighting in audio measurement

In broadcasting and audio equipment measurements 468-weighting is 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 with

noise band Noise is sound, chiefly unwanted, unintentional, or harmful sound considered unpleasant, loud, or disruptive to mental or hearing faculties. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibratio ...

s show increased sensitivity in the 5 to 7 kHz region on noise compared to tones. Other

weighting curve A weighting curve is a graph of a set of factors, that are used to 'weight' measured values of a variable according to their importance in relation to some outcome. An important example is frequency weighting in sound level measurement where a spec ...

s are used in

rumble measurement A rumble is a continuous deep, resonant sound, such as the sound made by heavy vehicles or thunder. In the context of Sound recording and reproduction, audio reproduction rumble refers to a low frequency sound from the Bearing (mechanical), bear ...

and flutter measurement to 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 the

kHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base uni ...

equivalent level). In the fields of acoustics and audio engineering, it is common to use a standard curve referred to as

, one of a set that are said to be derived from

equal-loudness contours 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. The unit of measurement for loudness levels is the phon and ...

Application to hearing in aquatic animals

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

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 the

sievert The sievert (symbol: SvPlease note there are two non-SI units that use the same Sv abbreviation: the sverdrup and svedberg.) is a derived unit in the International System of Units (SI) intended to represent the stochastic health risk of ionizin ...

or 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 meaningful

luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls wit ...

and

chrominance Chrominance (''chroma'' or ''C'' for short) is the signal used in video systems to convey the color information of the picture (see YUV color model), separately from the accompanying Luma (video), luma signal (or Y' for short). Chrominance is usu ...

signals 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 of

UV Index The ultraviolet index, or UV index, is an international standard measurement of the strength of the sunburn-producing ultraviolet (UV) radiation at a particular place and time. It is primarily used in daily and hourly forecasts aimed at the gener ...

, a weighting curve is used which is known as the McKinlay-Diffey Erythema action spectru

References

External links

Noise measurement briefing

{{Webarchive, url=https://web.archive.org/web/20161231170415/http://sound.whsites.net/project17.htm , date=2016-12-31
AES pro audio reference definition of "weighting filters"

Statistical analysis Applied and interdisciplinary physics