Aweighted

Aweighted, more commonly referred to as A-weighting or A-weighted measurements, is a standard method used in acoustics to approximate the human ear’s sensitivity to different frequencies. It is one of several frequency weightings designed to convert a noisy spectrum into a single representative level that correlates with perceived loudness at moderate sound levels. The A-weighting curve is derived from human audibility data summarized by equal-loudness contours and is implemented in measurement standards such as IEC 61672-1 and ANSI S1.4.

When applied to a sound pressure spectrum, the A-weighting network attenuates both very low and very high frequencies relative to midrange frequencies, effectively emphasizing the mid frequencies around a few kilohertz. The result is a single value called the A-weighted sound level, denoted L_A and expressed in decibels as dBA. In practice, sound level meters apply the A-weighting filter to instantaneous measurements and then compute time-averaged quantities such as LAeq, LA10, and LA90 for various monitoring purposes.

Applications and significance: A-weighted measurements are widely used for regulatory compliance, occupational noise exposure, and environmental noise assessments because they align reasonably well with typical human loudness perception at moderate levels. They are also common in consumer devices and product specifications.

Limitations: A-weighting is an approximation and may not accurately reflect perceived loudness for impulsive or highly tonal sounds, very high or very low frequencies, or unusual spectral content. For some assessments, C-weighting (dBC), Z-weighting (unweighted), or detailed spectrum analyses may be more appropriate. The term Aweighted is often used informally to indicate a dBA measurement.