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UMIK-1 calibration meaning? 1 year 3 months ago #54067

  • jffbaker
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Despite searching these forums, I don't see a straight and usable answer for the simple question "how do I use the Umik-1 Calibration" outside of canned software? I'm measuring with Matlab and Audacity, and need to know the dBFS output of the mic for a given dBSPL. For example:

The mic gives xxx dBFS for 94dBSPL sine wave stimulus at 1kHz. What is xxx? How exactly is it related to the 'Sens Factor' in the calibration file? And what is the relationship between Sens Factor and analog gain?

With a 1kHz 94dB stimulus, I measure about -22dBFS from the mic. That's with 18dB analog gain. With no gain that would have been -40dBFS, and with 36dB gain it would have been -4dBFs. With my Sens Factor of almost exactly +4dB, I think I can concluded the following:


The mic gives -36dBFS for 94dBSPL at gain = 0dB after adding the Sens Factor to the measurement
The mic gives -18dBFS for 94dBSPL at gain = 18dB after adding the Sens Factor to the measurement
The mic gives 0dBFS for 94dBSPL at gain = 36dB after adding the Sens Factor to the measurement

Is that all correct?

Thanks,

Jeff

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UMIK-1 calibration meaning? 1 year 3 months ago #54075

  • Ultrasonic
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The peak SPL that can be recorded exceeds 94 dB SPL. If your 0 dBFS is an absolute maximum signal level from the microphone then I don't think what you have posted is correct.

The simplest way to get a quick answer may be to compare what you get using REW to using Matlab and infer what is going on from this.

I've not seen an explanation of the calibration files posted and I'd suggest you contact miniDSP support for more information but you won't get a fast reply due to the Chinese new year holiday. Alternatively you could try asking on the REW forum as John Mulcahy must know the answer to have implemented it into REW.

www.avnirvana.com/forums/official-rew-ro...rd-support-forum.10/

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Last edit: by Ultrasonic.

UMIK-1 calibration meaning? 5 months 16 hours ago #58256

  • DBroadhurst
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The sensitivity or sens factor should be the microphone digital output dBFS with a 94dB SPL input, 94dB being 1 Pascal.
Understanding Microphone Sensitivity | Analog Devices

HOWEVER this doesn't seem to be the case for the UMIK-1.

JohnM REW author offers an explanation here,
Understanding SPL offset (UMIK-1) | Home Theater Forum and Systems (hometheatershack.com)

"The cal file sensitivity figure is the dBFS input reading for 100 dB SPL with the input volume set to 100%, which is 24 dB of digital gain. The UMIK internal gain (18 dB in your case) is taken into account in the cal file sensitivity figure."

The 24 dB of digital gain refers to having the microphone level control turned up to maximum in the microsoft windows device properties.
The 100 dB SPL reference level for the calibration is also not the standard, 94 dB SPL is which is the level generated by microphone calibration devices you can buy.

Would be good if MiniDSP published this info in the sensitivity figures.
I'm not sure if the UMIK-2 is the same or not.

 



 

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