Gain is the term used to describe how much of the audio signal is being increased or decreased from the source.
Typically, most audio professionals operate their input channel levels at unity gain.
This means the fader of the channel will be at ‘0’ on the fader bank and the gain rotary will be adjusted accordingly to achieve an appropriate operating level.
An appropriate operating level is usually achieved between green and orange meter readings, which on our consoles is between 0 and -6dBfs. If an input or output starts to peak, which on our consoles causes a red PK meter to be activated, then you are not at a safe operating level.
The term safe operating level is being used when referring to issues such as feedback, distortion and exceeding the recommended decibel unit for human hearing over a period of time.