Mackie DL806 Reference Manual page 77

FX Returns — There are two vertical return channel faders and
meters, one for each effect. These control the return level from
the effect to the selected output. You have seen these before,
as they are the same faders displayed in the mixer view. A pair
exists [one for reverb, one for delay] for each selected output.
Unlike the FX sends, the color of the selected output indicator
will change based on the selected output for the FX returns.
See the image to the right for one example.
Navigate to the reverb return channel, then move the channel
fader up and down. Notice that it also moves the reverb return
fader up and down. This is because they are both showing the
same level. As such, moving the return reverb fader up and
down also moves the reverb channel fader up and down.
This works with the delay return channel and delay return
fader, as well.
Mackie DL806 and DL1608 Reference Guide
There are no reverb or delay returns to the reverb
and delay sends (which would be crazy...and it avoids
a feedback loop), so when either the reverb or delay
send is the selected output, there are no return faders
as seen in the image to the left.
The astute reader may ask if there are no sends from
returns and no returns from sends, what if one selects
an effect return as the current channel and an effect
send as the selected output. Good question! The image
on the left shows the FX with no sends and no returns.
Of course you may still adjust the global controls.
If you want to witness this for yourself here's how
in two simple steps: (1) go to either the reverb channel
or delay channel and (2), select reverb or delay as the
output. Done!
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