A microphone delivers a signal of 1 mV up to around 1 V (in extreme conditions).
The microphone preamplifier is specially designed to amplify this as necessary up to around 1 V on peaks and deliver a low noise signal to the following circuitry.
The amount of gain is set using the Gain control.
The microphone input will supply 48 V phantom power to the microphone.
The line input accepts signals of around 100 mV to 1 V and provides amplification as necessary.
On some consoles, there is no gain control on the line input.
The phase button inverts the signal.
The filter cuts low frequencies below around 100 Hz.
The pad button attenuates the signal, usually by 20 dB.