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TOPIC: Re: UMIK-1 SPL Calibration

UMIK-1 SPL Calibration 7 years 9 months ago #7429

  • rymar
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After reading the REW threads, and looking here, I am still not clear on how to set the SPL calibration level on my UMIK-1.

I have adjusted the Windows mic recording level to 100%; is this correct?

My mic calibration file has as the first line:
"Sens Factor =-14.733dB, SERNO: 7000115"

This looks like a comment, and changing the Sens Factor value and reloading the cal file into REW doesn't make any difference in the SPL reading.

So, is this number (-14.733dB) an SPL calibration number? Where do I enter this number in REW to ensure a calibrated SPL reading?

I have already used my UMIK-1 to re-equalize my car audio installation (which uses 2 mini-DSPs for front/sub, and rear speaker equalization).

The UMIK-1 is fantastic! It is really nice not to have all the cables and clutter of an external mic preamp and mixer, and the noise level is way lower with the onboard A-D. 5 out of 5 stars!


Thanks!
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Re: UMIK-1 SPL Calibration 7 years 9 months ago #7444

  • JohnPM
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If you use the latest REW V5.01 beta 10 the UMIK SPL calibration figure is read automatically by REW when you load the cal file, you don't have to enter anything.
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Re: UMIK-1 SPL Calibration 7 years 9 months ago #7446

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Thanks for the reply!
I just installed REW V5.01 beta 10, and can now see that the cal file parser is reading the SensFactor value and storing it in the registry entry "HKEY_CURRENT_USER\Software\JavaSoft\Prefs\room eq wizard\last/Spl/Offset. It looks as if the UMIK-1 sensitivity factor value is referenced to 120dB, and the sensitivity factor is subtracted from 120db (resulting in a last/Spl/Offset value of 134.733 for my mic).
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Re: UMIK-1 SPL Calibration 7 years 9 months ago #7583

  • mcmahongg
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Hi

Does this mean that (for this example) 134.733 dB SPL is equivalent to 1000 mV RMS out of the microphone output - giving a microphone sensitivity of 9.2 mV/Pa?
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Re: UMIK-1 SPL Calibration 7 years 9 months ago #7612

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Well, I'm not sure that we can know (or should care) what the actual voltage level of the signal is from the microphone capsule, since the 24 bit A-D converter is built into the UMIK-1, and I'm sure there is a preamp before the A-D. I'm guessing that at 134dB SPL, the digital values from the UMIK-1 are pretty close to full scale, as this makes the best use of the A-D range.

With a little experimentation, it should be possible to determine the exact gain from SPL to the UMIK-1 digital output:

1) Set up a test tone generator, UMIK-1, and REW (using the cal file) to generate a known SPL level.
2) Quit REW, and capture the UMIK-1 output into a wave editor.
3) Measure the peak-to-peak digital signal from the wave values, and convert to RMS.

This will give the gain for a particular mic from SPL to digital values.
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Re: UMIK-1 SPL Calibration 7 years 9 months ago #7614

  • JohnPM
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Or just read the dB FS values from the REW SPL meter...
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Re: UMIK-1 SPL Calibration 7 years 9 months ago #7617

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That sounds way too easy ... ;-)
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