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  1. A frequency-response adjustment of a sound-level meter that makes its reading conform, very roughly, to human response. The human ear is most sensitive to sound at mid frequencies (500 to 4,000 Hz) and is progressively less sensitive to sound at frequencies above and below this range. A-weighted sound level is the most commonly used descriptor to quantify the relative loudness of various types of sounds with similar or differing frequency characteristics.
  2. A weighting methodology used to account for changes in human hearing sensitivity as a function of frequency. The A-weighting network de-emphasizes the high (6.3 kHz and above) and low (below 1 kHz) frequencies, and emphasizes the frequencies between 1 kHz and 6.3 kHz, in an effort to simulate the relative response of human hearing. Source: http://www.volpe.dot.gov/acoustics/docs/1990-1999/1999-1.pdf
  3. A frequency-response adjustment of a sound-level meter that makes its reading conform, very roughly, to human response. Source: http://www.owenscorning.com/around/sound/glossary.asp