ANSI A-Weighting

The A-weighting curve for sound measurement specified by ANSI. It employs a wide bandpass filter centered at 2.5 kHz, with ~20 dB attenuation at 100 Hz, and ~10 dB attenuation at 20 kHz, so it tends to heavily roll-off the low end, with a more modest effect on high frequencies. It is basically the inverse of the 30-phon (or 30 dB-SPL) equal-loudness curve of Fletcher-Munson. Although in terms of the human hearing, it is an accurate curve, at least at low to moderate volume levels. A-weighting tends to favor equipment that might otherwise be considered “noisy” because it can decrease the overall spec’s representation of 60Hz hum and high frequency hiss that could be present.