# Implications of UMIK-1 shipping with -18dB gain?



## lovingdvd (Jan 23, 2007)

I received my UMIK-1 mic last week and was a bit surprised to see that, as REW identified it as -18dB. I've read elsewhere that it seems that new UMIK-1 mics are being shipped with -18dB gain instead of -12dB gain.

What would be the advantage for them to want to make this change to -18dB? And what implications does this have for use with REW? Are there any changes in the REW preferences or setup/settings I should use to compensate for this difference?

I am having difficulties trying to measure at high SPL without clipping, whereas it seems others can measure at higher SPLs without clipping that are using the mic with -12dB. Is this related to the -18dB gain on my mic? 

I run my sub "hot" - about +10 dB over what would be a flat FR with the rest of the system. As such, I can't seem to take any measures much past 80dB without REW saying it ran out of headroom and warning me about clipping. 

In particular I want to see how loud I can play my sub and speakers without introducing much distortion, and to see at what point the distortion starts to ramp up. Sub dB at reference is like 105dB or 115dB right? Doesn't seem like I could even get close to measuring at those levels without clipping. How can this be done?

Thanks!


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## JohnM (Apr 11, 2006)

The mic sensitivity was increased to improve signal to noise ratio at normal measurement levels - I think Dirac were keen that was done to get good correction results with Dirac Live. There are no implications for REW, the sensitivity figure in the mic's cal file takes account of the gain setting.

The max input level before clipping for an 18 dB gain mic is 100 dB, give or take a dB. Make sure the input volume is set to the 0 dB level for the mic - for Windows 8 that is normally 52%, you can toggle the windows volume control display between % and dB by right clicking on it. If you have the input volume set to 100 you will clip very easily as that is applying 24 dB of digital gain.

If you want to measure levels over 100 dB you will need to open the mic and change the gain settings, then adjust the sensitivity figure in the cal file accordingly. It is probably not necessary though. To measure the power level that starts to cause significant distortion on your sub you are best using the CEA-2010 test signal, it was designed for that purpose - see the help - and use the RTA to check the result.


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