Focusrite Scarlett 18i20 User Manual page 29

Monitor control enable buttons (1 to 10)
These buttons select which line outputs of the Scarlett 18i20 are affected by the other GUI monitor
section controls, and also the front panel monitor controls. Depending on your monitoring set-up,
you can control no speakers, just a single pair of speakers, or up to 10 speakers simultaneously.
Note: the levels at all the digital outputs on the Scarlett 18i20 are unaffected by Scarlett MixControl's
monitor section controls. If you need to route individual DAW tracks to digital outputs, adjust the
output levels from the DAW.
The ten buttons determine the control status of the ten line outputs. There are three states; clicking
on the buttons toggles between blue and red states; clicking while holding SHIFT down puts them in
the grey state.
When the button is blue, the level of the line output is controlled by the GUI monitor section.
When the button is red, - the line output is muted.
When the button is grey, the level at the line output is fixed at full volume and is not controlled
by the GUI monitor section.
WARNING: The 'grey' state should be selected when a line output is to be
used to drive external processors. Note that in this state, the signal routed to that
output will be at full level. Should you have amplifiers/loudspeakers connected
to the output, this may result in a very high sound level in your monitor speakers
or headphones. Always check your levels (in your DAW or the Scarlett MixControl
Mixer) before setting the monitor button to this mode.
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