Antares autotune, som TC Electronics multi effects, a bunch of compressors, gates etc. The usual stuff
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The MOTU unit is a world clock master. I use it to sync all the Digidesign interfaces to 48khz for a more stable clock signal
Some clocks fade off over time, so interfaces may have different hz-settings even though they are set to 48khz.
100-500hz difference between the interfaces is enough to give some digital noise in the recording when recording with multiple interfaces at once.
You could use one of the Digidesign interfaces as the master clock as well, but I had the MOTU clock since before and it fills out the rack nicely