Frequency Weighting (spectral analysis)

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 a spectrum of frequencies.

Weighting in acoustics

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 applicable to human hearing 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 correct only 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.

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 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.

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 fields 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.

Application to hearing in aquatic animals

Auditory frequency weighting functions for marine mammals were introduced by Southall et al. (2007) and updated in 2019 . Auditory frequency weighting functions for fishes and invertebrates were introduced by Lucke et al. (2024).