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Discussion Starter · #1 ·
I recently got the Mobile Pre USB soundcard and a calibrated Dayton EMM-6. I went through the steps and performed Soundcard Calibration, checked levels and calibrated the SPL readings. But when I try to perform a measurement, it gives me a decent result for low frequencies, but at higher frequencies it says my signal is getting clipped. I thought the check levels should have checked for that? I am confused, so looking for help in getting this working properly.

My connections:
Input: Ch1 Mic - XLR cable to EMM-6; Ch1 and Ch2 gains in the front of unit at maximum. Input channel in Preferences set to Left.
Output: 2/R - 1/4" to dual RCA splitter -> L and R inputs of Aux input on receiver

In Volume Mixer, the "REW V5" volume is at max when I get the clipping message (all calibrations were done at this setting). If I reduce this to 50%, I get a graph like the following, but I am not sure if I should be even doing that (reducing REW V5 volume level in mixer to 50%)? So, what am I doign wrong?

Thanks for the help!

full range - 11-19pm.jpg
 

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Leave the REW volume in the Windows mixer at 100% but reduce the Ch1 gain so that you have at least 3dB headroom (as shown on the measurement dialog) when you make a measurement.
 

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Discussion Starter · #3 ·
Thanks - will try that tonight.

Do I need to recalibrate anything for this change - levels / SPL?
Also, does the graph in general look like what can be expected of a typical room? Is it 'normal' for the graph to look almost like a band at higher frequencies when no smoothing has been applied, or is it just because of the logarithmic nature of the scale?
 

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If you make any change to the gains in the input path the SPL meter needs to be recalibrated to allow REW to know the new relationship between the level it sees from the soundcard and the actual SPL.

The appearance of the trace you posted is normal, especially if you had both speakers active which adds to the comb filtering if their distances from the mic are not identical. Smoothing removes the distraction of the comb filtering. The region below 200Hz is substantially higher than the remaining range, applying some smoothing will make the difference in levels more obvious.
 
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