spl meter significant difference in lower db

[champagnecharly]

Hello,

I have a couple of spl meters running through a digirack2. i have only done a simple calibration with a field calibrator as noise source. 114db. what i find is if post calibration i turn on the calibrator/ monitor noise it produces the software will give accurate readings. however once the device is removed and monitoring normal noise levels there is a considerable discrepency between rew results and thoese on the device with rew not going below 50dbC(f) any ideas why this would occur? I read calibration files are for offfset on frequency bands however i cant see how this would cause the rew readings to be so high. any thoughts?

 

[John Mulcahy]

I'd guess you are seeing the noise floor of the meter's analog output, which may be higher than its internal path for processing the captured signal. If the meter switches gain for lower levels the analog output may also have its gain changed and so be offset by the gain change.