TOPIC: Re: UMIK-1 SPL Calibration

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!

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.

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).

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?

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.

Or just read the dB FS values from the REW SPL meter...

That sounds way too easy ...