Gregory Pencheff wrote:

Not sure we’re following where the error is occurring.   Are you seeing the “Audio engine inactive” error in the standalone version of SD3 or when you are using the VST plugin in Reaper?

If you see the error in the standalone version check to see what audio interface you have configured.  You’ll find that under the Settings menu, Audio/MIDI setup.  If you’ve connected a new piece of gear to your Windows computer that includes an audio interface Windows may have changed your SD3 settings to use the new interface.  And, if that new piece of gear is currently turned off, well… SD3 then tells you the interface is inactive.

My primary audio interface is internal to my Soundcraft mixer but I also use have my Line6 Helix connected to the PC via USB and the Helix has it’s own audio interface.  When I update the firmware on the Helix Windows switches some sound settings to use the Helix’s interface.  Then I don’t have any sound from the PC.  Always throws me for a loop until I check the various programs settings to see which ones are trying to send sound to the Helix interface.

Just a thought… this may not be your issue but it’s worth checking.

Superior Drummer 3 version: 3.3.1
Operating system: Windows 10

Problem solved !

it was a setting in Reaper !