Sound meters incorporate a processing network that assigns relative importance to low, middle, and high frequency signals. By comparing differently weighted measurements, you can isolate the source of problem sounds. "A" Weighting attenuates the lower frequencies to approximate the response of the human ear, which is most sensitive to frequencies between 3000 and 4000 Hz. "B" Weighting gives decibel readings of combined high and middle frequency signals; use in conjunction with "A" weighting to isolate sounds that are causing a problem. "C" Weighting reads all frequencies the same but gives a better response to higher frequencies than "A" or "B" weighting. Use to pinpoint problems when "A" or "B" weighted scale readings are very high.