Silence measured with REW RTA and suspicious calibration files

[serial]

Hi,

I'm concerned about the correctness of my UMIK-1 calibration files after I've measured silence with REW RTA. I bought the mic not from Cross-Spectrub Labs, so the files are downloaded from the minidsp website.

On the graph, you can see 4 measurements - spectrum mode vs RTA 1/48 octave mode, and 90 degreee calibration file vs no calibration file. The horizonal lines are recorded with RTA 1/48 octave mode, the downward sloping lines are with the spectrum mode. The lines which look smooth between 3 kHz and 20 kHz are recorded without a calibration file, and the lines which go up from 7kHz are with the 90 degree calibration file.

The line around 0 dB is the calibration file itself.

The measurements with the calibration file look pretty weird and not natural. Can someone confirms that they do not look correct? If yes, what can I do? Can I assume that silence is supposed to produce a horizontal line in the RTA mode and create my own calibration file from the measurement I get?

 

[serial]

Well, maybe the 90 degree calibration file is not supposed to be used in this case because we don't have a sound source, so here is the same with the 0 degree calibration file:

 

[MaxwellsEq]

I don't think anyone will know what silence should look like at your location. Even so, I think it's unlikely that it will be a horizontal line or even a slope of some type.

 

[JohnPM]

The calibration file compensates for the response of the mic in the presence of a signal. At very low signal levels the mic's self-noise will become the dominant component and the calibration file would no longer be appropriate.