Weighting
From Wikipedia, the free encyclopedia
The process of weighting involves emphasising some aspects of a phenomenon, or of a set of data — giving them 'more weight' in the final effect or result. It is analogous to the practice of adding extra weight to one side of a pair of scales to favour a buyer or seller.
While weighting may be applied to a set of data, for example epidemiological data, it is more commonly applied to measurements of light, heat, sound, gamma radiation, in fact any stimulus that is spread over a spectrum of frequencies.
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[edit] Weighting and loudness
In the measurement of loudness, for example, a weighting filter 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 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 only correct at a level of 40-phon and other curves known as B, C and D weighting are also used, the latter being particularly intended for the measurement of aircraft noise.
[edit] 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, only really apply to tones, as tests with noise bands show increased sensitivity in the 5 to 7 kHz region on noise compared to tones.
Other weighting curves are used in rumble measurement and flutter measurement to properly assess subjective effect.
[edit] 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, while letting through those that do the most damage, so that any source of radiation may be measured in terms of its true danger rather than just its 'strength'. The resulting unit is the sievert or microsievert.
[edit] Weighting and television colour components
Another use of weighting is in relevision, where 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 and chrominance signals for transmission.
[edit] 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, a weighting curve is used which is known as the McKinlay-Diffey Erythema action spectrum [1]
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 phon (1 kHz equivalent level).
In the field of acoustics, and audio engineering, it is common to use a standard curve referred to as A-weighting, one of a set that are said to be derived from equal-loudness contours.
[edit] Weighting and 3D modeling
Weighting in the context of a 3D model refers to the effect the bone has on surrounding verticies. "Bone A" might affect some verticies with 80% speed but others with 40% speed in order to simulate more fluid movements ie a page turning. Using a book as an example: if all the verticies in a page were assigned the same weight the pages would stick straight out through the turn, but if the pages at the spine are given 100%, those mid-way given 80% and those at the edge given 60%, the page would curve realistically when turned.
