Adjustment curve A

Professional Definition

The A-weighting curve is a set of correction values applied at individual frequency bands f, aimed at approximating the frequency response of the measurement device to the characteristics of human hearing at low levels of sound pressure (about 40 phons).

In engineering practice, this means applying a filter that strongly attenuates low frequencies and to a lesser extent very high frequencies, while slightly boosting the range of 2–4 kHz, to which the ear is most sensitive. The measurement result using this curve is expressed in dB(A) units.

Acoustics in Simple Words

Imagine that your noise meter is a pair of sunglasses, and sound is light. A regular uncorrected (linear) meter sees all light equally bright – both the dazzling and the neutral. Activation of the A-weighting curve is like putting on special lenses that dim those colors (frequencies) to which our eyes (ears) are less sensitive (e.g., very low bass), while allowing through what actually impacts our discomfort. As a result, the reading on the display tells us not about the physical energy of the wave but about how loudly this sound is "felt" by a human.

Summary

The A-weighting curve is a standard in environmental and industrial noise measurements (Occupational Safety and Health). It allows for assessing the harmfulness of sound in relation to the perception of the human ear, ignoring those spectral components that we hear poorly or not at all.