Aweighting

A-weighting is a frequency weighting used in sound measurement to approximate the sensitivity of the human ear. Implemented as a filter (analog or digital), it shapes the measured sound pressure level so that the resulting value, expressed in decibels as dB(A), aligns more closely with perceived loudness at moderate sound levels. A-weighting is defined in international standards for sound level meters, such as IEC 61672 and ANSI S1.4.

Origin and rationale: The weighting draws on the historical equal-loudness contours described by Fletcher and Munson, refined into standard curves. The A-weighting curve emphasizes mid frequencies around 2 to 3 kHz and attenuates both low frequencies (below about 100 Hz) and high frequencies (above about 6 kHz). This shape mirrors the ear’s relative sensitivity across the audible spectrum under typical listening conditions.

Applications: A-weighted measurements are the de facto standard for environmental noise assessment, workplace noise exposure limits, and many consumer electronics tests. Readings are commonly reported as L_A and may be paired with time-weightings (such as slow or fast) depending on regulatory or testing requirements.

Limitations: A-weighting is an approximation and does not measure perceived loudness directly. It can misrepresent very loud sounds, impulsive noises, or noise with unusual spectral content. For more precise loudness estimation, other scales or weightings may be used, such as C-weighting for peak levels, Z-weighting for flat response, or phons and sones for loudness perception.

See also: dB, dB(A) measurements, sound level meter, weightings (C-weighting, Z-weighting), equal-loudness contours.