This applies to: Scarlett 18i20, Scarlett 18i8 3rd Gen, Clarett ranges, Saffire range

By default, the monitor control on Focusrite interfaces will only affect outputs 1-2. If you're finding that adjusting the monitor control doesn't change the level being fed to connected equipment, please first check that you've connected said equipment to output 1-2.

On some interfaces, you can assign multiple outputs to the Monitor control to support a variety of monitoring use cases such as surround mixing setups. However, you can also unassign the Monitor control from your outputs which means the Monitor control has no effect on the level of the signal going to any outputs on your interface.

If you find this is the case, and you want control over the output using the hardware monitor dial, go to your control software and select the outputs you want to control in the 'Monitor Controls' section.

In this screenshot the Monitor dial controls Outputs 1-2:

The Monitor Controls section also applies to any Dim or Mute switches on your interface.