Thanks Stephan for borrowing me the device. The following tests are all USB powered BUS POWER with no AA batteries inside.
I’ve asked the audioengineering Reddit community and they removed my post.
A Youtube link from Stephan informed me that the DR-40 suffers from high noise preamps, resulting in a high noise floor.
Solution: I’m not sure yet. Post processing?
Lowcut filter 40Hz
Lowcut filter 80Hz
Lowcut filter 120Hz
Lowcut filter OFF
With no Inputs
Alarming noisy... white noise? How does one get clear audio straight out of a recorder?
I.e. no BUS POWER, 3 fresh Alkaline batteries
With no inputs
It’s very similar to Julian Krause’s test here https://youtu.be/ZvqQ2ejq6og?t=487