Unity gain
What is unity gain? Unity gain means that the input level is equal to the output level.
When does unity gain matter? It is not important when connecting the device to an amplifier or mixing console. It is important in setups where the device is being used as an effects-only processor (e.g. as a pedalboard or in an amp's effects loop) or when using the Four-Cable-Method (4CM) to connect to a guitar amplifier.
How do I set up for unity gain? To set up an output for unity gain, set the corresponding Output knob to its maximum position. Note: this does not apply to all devices, check the manuals. It does apply to outputs 3 and 4 of the Axe-Fx III, output 3 of the FM9, and output 2 of the FM3
Пишут, что unity gain нужен, если акс используется только как процессор эффектов, чтобы выровнять уровень входного и выходного сигнала.