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.
In the measurement of loudness, for example, a weighting filter is commonly used to emphasise frequencies around 3–6 kHz where the human ear is most sensitive, while attenuating very high and very low frequencies to which the ear is insensitive. 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'.
Another use of weighting is in Television, 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.
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.
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.
