A circuit or system that has its voltage gain adjusted to be one, or unity. A signal will leave a unity gain circuit at the same level at which it entered. In Mackie mixers, unity gain is achieved by setting all variable controls to the marked "" setting. Mackie mixers are optimized for best headroom and noise figures at unity gain.
Unity Gain, is the position on a Gain or Volume control or Fader, where the control is niether cutting or boosting the sound.....The level before the amp is equal to the level after the amp.