I recently purchased a UMIK-1 to use with REW for calibrating speakers, and I ran into a question when I was performing initial checks in REW: When I open the SPL meter and let it log sound without playing anything (just recording background ambient sound, no pink noise or anything of that sort), it shows a baseline level of ~70dB (see attached image for reference). The only background noise in the room is generated by some quiet computer fans, and I've previously measured the ambient sound level in my room with a cheap SPL meter to be in the 40dB range. Am I misunderstanding what that meter in REW is meant to show or using settings wrong? The only thing I did within REW was apply the MiniDSP calibration file to the mic input. My room obviously does not have 70dB of background noise, or I wouldn't be able to think straight, so I figure something else peculiar must be going on with the measurements.