It's always the same. The right input to the Behringer unit has no effect (well it does register at very low level i.e. 40 dB down) and the left input is at full volume on both channels and records at equal volume on both the L and the R Reaper channel, or to both Reaper tracks if switched that way.Have you checked the cable you are using to go from synth to interface. What happens if you swap it around, i.e. right into left and vice versa?
Have you listened to your Synth into a Amp? Just to make sure your left and right outputs are putting out the same level.It's always the same. The right input to the Behringer unit has no effect (well it does register at very low level i.e. 40 dB down) and the left input is at full volume on both channels and records at equal volume on both the L and the R Reaper channel, or to both Reaper tracks if switched that way.
This was the answer. The Windows input was set to 16-bit mono DVD quality. Now I've set it to 16-bit stereo DVD quality both channels appear in Reaper. Thanks to all who helped.I suspect the issue is in the settings in Windows - Settings - Sound Devices - Input. Check the Device Settings as well. (are you in Win 10 or 11?)
If Windows isn't sending stereo info to Reaper, then there's nothing Reaper can do to fix it.