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. The most commonly known example is
frequencyFrequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
weighting in sound level measurement where a specific set of weighting curves known as A, B, C and D weighting as defined in IEC 61672 are used. Unweighted measurements of sound pressure do not correspond to perceived loudness because the human ear is less sensitive at low and high frequencies, with the effect more pronounced at lower sound levels. The four curves are applied to the measured sound level, for example by the use of a
weighting filterA weighting filter is used to emphasise or suppress some aspects of a phenomenon compared to others, for measurement or other purposes.- Audio applications :...
in a sound level meter, to arrive at readings of loudness in
PhonThe phon was proposed in DIN 45631 and ISO 532 B as a unit of perceived loudness level LN for pure tones by S. S. Stevens.-Definition:The purpose of the phon scale is to compensate for the effect of frequency on the perceived loudness of tones...
s or in decibels (dB) above the threshold of hearing. (see
A-weightingA 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. The most commonly known example is frequency weighting in sound level measurement where a specific set of weighting curves known as A,...
).
Weighting curves in Electronic Engineering, Audio and Broadcasting
Although A-weighting with a slow rms detector, as commonly used in sound level meters is frequently used when measuring noise in audio circuits, a different weighting curve, ITU-R 468 weighting uses a psophometric weighting curve and a quasi-peak detector. This method, formerly known as CCIR weighting, is preferred by the telecommunications industry, broadcasters, and some equipment manufacturers as it reflects more accurately the audibility of pops and short bursts of random noise as opposed to pure tones.
Psophometric weightingPsophometric weighting refers to any weighting curve used in the measurement of noise. In the field of audio engineering it has a more specific meaning, referring to noise weightings used especially in measuring noise on telecommunications circuits...
is used in
telephonyIn telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....
and telecommunications where narrow-band circuits are common.
Other applications of weighting
Acoustics is by no means the only subject which finds use for weighting curves however, and they are widely used in deriving measures of effect for sun exposure, gamma radiation exposure, and many other things. In the measurement of gamma rays or other ionising radiation, a radiation monitor or
dosimeterDosimeters measure an individual's or an object'sexposure to something in the environment — particularly to a hazard inflicting cumulative impact over long periods of time, or over a lifetime...
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
sievertThe sievert is the International System of Units SI derived unit of dose equivalent radiation. It attempts to quantitatively evaluate the biological effects of ionizing radiation as opposed to just the absorbed dose of radiation energy, which is measured in gray...
is a unit of weighted radiation dose for ionising radiation, which supersedes the older unit the
REMNamed after Wilhelm Röntgen , the roentgen equivalent in man or rem is a unit of radiation dose equivalent...
(roentgen equivalent man).
Weighting is also applied to the measurement of sunlight when assessing the risk of skin damage through
sunburnA sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...
, or when assessing the sun protection factor of
sun-screenSunblock is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet radiation on the skin exposed to sunlight and thus helps protect against sunburn...
lotions. Light,
UVAUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
and UVB in sunlight have different effects, with regard to both DNA damage and
melaninMelanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...
stimulation, depending on the wavelength of the radiation. Weighted measurements are often in SU (
sun unitThe sun unit is a measure of sun intensity weighted for skin damage related to the UV index.-Basics of solar radiation:Solar radiation sustains life on earth and determines climate...
s) or DUV (
Diffey weighted UV irradiance). The
UV indexThe ultraviolet index or UV Index is an international standard measurement of the strength of the ultraviolet radiation from the sun at a particular place on a particular day...
is also used.
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
chrominanceChrominance is the signal used in video systems to convey the color information of the picture, separately from the accompanying luma signal . Chrominance is usually represented as two color-difference components: U = B' − Y' and V = R' − Y'...
signals for transmission.