A-Weighting

An electrical filter which used when taking audio measurements of equipment, and designed to mimic the relative insensitivity of the human ear to high and low frequencies at low sound pressure levels (notionally 40 Phons or about 30dBA SPL). Essentially, the filter rolls-off the low frequencies below about 700Hz and the highs above about 10kHz. This form of weighting filter is often used when making measurements of low-level sounds, like the noise floor of a device. (See also C-Weighting and K-Weighting.)