Ah, Nooelec RTL-SDR. Sorry, missed that one. Not sure then.
The way I calibrate Visual Gain is to have no antenna connected then adjust visual gain for zero S-Points on the received noise floor.
If you do this in both V3.2 and V3.3 do you see a difference in the Visual Gain setting required? My guess is it will be this and the difference is not due to actual signal reduction but some change to the calibration of the Visual Gain introduced by a processing change between versions. V3.2 is now many many months of programming and a huge number of changes behind V3.3. Maybe Simon will comment if he can remember changing anything that would affect the Nooelec Visual Gain setting?
73
Max