The sound pressure measured is not the same as that received by the human ear. To balance this out, the measured result is subjected to a method known as A-weighting. Here, the signal is amplified differently across different frequencies, with the lower frequencies, to which the ear is less sensitive, amplified to a lesser extent, as shown in the weighting curve. The sound level is stated in Decibels (A)=(dB(A)). The B-weighting and C-weighting are used to adjust to different requirements (Figure S 8).
Figure S 8: Weighting of the noise level