While using the interface as your computer's audio output device, media keys on many systems may no longer work to adjust system audio volume.
Use the Monitor knob on the front panel of the interface to adjust volume.
Press the Inst button on the front panel to switch the corresponding input to high-impedance.
Turn up the Gain knob on the corresponding channel to set the amplification of your signal.
How to adjust my mic gain?
1) Try with another cable to see if it solves the issue.
2) If you are using a dynamic microphone, check the user manual of your microphone to see how much gain it requires. The MiniFuse is delivering a gain of 56dB.
3) If you are using a condenser microphone, check the user manual of your microphone to see if it needs phantom power. If so, press the 48v button, that will supply the required current to your microphone.