noise meter
The A network simulates the response of the human ear to the 40-square pure tone in the equal-loudness curve, and its noise meter curve shape is opposite to the 340-square equal-loudness curve, so that the middle and low frequency bands of the electrical signal have greater attenuation;
The B network simulates the response of the human ear to a 70-square pure tone, which makes the low frequency band of the electrical signal attenuated to a certain extent;
