Measurement based roughly on the uneven frequency sensitivity of the human ear. The influences of low and high frequencies are reduced in comparison to midrange frequencies because people are most sensitive to midrange sounds.

The filtering system in a sound meter that allows the meter to disregard lower frequency.

a frequency weighting network corresponding approximately to the sensitivity of the human ear

The filtering of sound that replicates the human hearing frequency response. The human ear is most sensitive to sound at mid frequencies (500 to 4,000 Hz) and is progressively less sensitive to sound at frequencies above and below this range. A-weighted sound level is the most commonly used descriptor to quantify the relative loudness of various types of sounds.

The A-weighting curve is one of a family of curves defined in IEC179 and various other standards for use in sound level meters. Though originally intended only for the measurement of low-level sounds (around 40-phon) it is now commonly used for the measurement of environmental noise and industrial noise, when assessing potential hearing damage and other noise health effects at moderate to high intensity levels. A-weighting also finds widespread use in audio equipment measurement, though arguably it may not be the most suitable weighting for this purpose.