A-Weighting. The human ear is not equally sensitive to all frequencies and we do not hear low-frequency sounds as well as those in the mid-frequencies (500-1000 Hz). A sound-level meter can measure a wide range of frequencies with equal sensitivity of the ear. This is known as “A weighting” and measurements made with this filter switched in are denoted as dB(A). Most measurements of overall noise (that is, including all frequencies) are made as dB(A).