The AD-10's GND switch reduces ground hum or buzz on the XLR OUT L and R jacks.
When you connect the AD-10 to other devices, grounding can conflict between units and cause hum or buzz. Setting GND to LIFT disconnects the ground path for XLR OUT L/R only, which often clears the noise.
Keep the switch on NOR (normal ground). Switch to LIFT only if you hear ground hum or buzz.
This switch applies to XLR OUT L/R only. It does not affect LINE OUT L/PHONES or R/MONO.