Many popular domestic and imported amplifiers and attenuators currently use two-stage amplifiers in amplification circuits, namely input amplifiers and output amplifiers, whose function is to amplify weak electrical signals. The input attenuator and output attenuator are used to change the attenuation of the input signal and the output signal, so that the pointer of the meter is in the appropriate position, and the attenuation of each gear is 10 decibels. The adjustment range of the attenuator used in the input amplifier is the measurement bottom (such as 0-70 decibels), and the adjustment range of the attenuator used in the output amplifier is the measurement high end (70-120 decibels). The dials of the input and output attenuators are often made in different colors, and currently black and transparent are commonly paired. Due to the fact that many sound level meters have a high and low limit of 70 decibels, it is necessary to prevent exceeding the limit during rotation to avoid damaging the device.