# Calibrated mic setup for sensitivity



## tnargs (Sep 7, 2006)

Hi,

I have been successfully using my calibrated mic with .frd file in REW for some years.

It corrects for frequency response, but I assumed it doesn't correct for sensitivity / SPL.

However, I recently came across a message in REW that I don't need to go through the sensitivity calibration process in REW (you know, the one using a separate SPL meter reading as a reference point to set REW's SPL readings), if I have a microphone calibration that includes a sensitivity measurement for the mic.

Well, the calibration 'certificate' I received from Cross-Spectrum with my mic DOES include a sensitivity response measurement ( -31.7 dB ref 1 mV/Pa, at 1000 Hz). In fact it includes a graph of that value vs frequency, as it varies a little from -31.7 across the octaves, but not much.

So..... how do I utilise this in REW, so that REW's SPL tool reads correct SPL values? I would much rather do it this way than the 'standard' method, since I don't have a high quality SPL meter.

cheers


----------



## JohnM (Apr 11, 2006)

That only applies to some models of USB mic (UMIK-1, UMM-6, Omnimic). It can't be applied more generally as REW only receives input volume settings (from JavaSound) as a 0 to 1 figure, it doesn't get the corresponding dB figure (the mapping between the linear volume percentage and the dB attenuation or gain varies between operating systems and devices) so it doesn't know how to take into account the volume setting. In the case of the USB mics that mapping data has been collected and is compensated for.


----------



## tnargs (Sep 7, 2006)

OK, thanks.

Is there any way that I can 'manually' calculate from my mic's sensitivity figure, through the preamp's gain, to manually set the correct SPL figure in REW? Instead of relying on an uncalibrated SPL meter?


----------



## JohnM (Apr 11, 2006)

Yes, John Reekie has done the hard work for you in describing the process at https://johnr.hifizine.com/2013/03/room-eq-wizard-spl-calibration-without-an-slm/


----------



## oweee (Apr 2, 2015)

While we are on this subject I have recently purchased a UMIK-1 & was wondering if the sensitivity calibration file was correct for SPL as it didn't seem to be right to me then I discovered that the sensitivity for the UMIK-1 is variable via the mac os system preferences. So my question is at what level is the correct setting so the SPL reading is correct when using REW's SPL meter?


----------



## JohnM (Apr 11, 2006)

oweee said:


> While we are on this subject I have recently purchased a UMIK-1 & was wondering if the sensitivity calibration file was correct for SPL as it didn't seem to be right to me then I discovered that the sensitivity for the UMIK-1 is variable via the mac os system preferences. So my question is at what level is the correct setting so the SPL reading is correct when using REW's SPL meter?


By 'sensitivity is variable' are you referring to the input volume control? REW reads the volume control setting and takes into account the effect it has on the UMIK's internal gain setting. For that to happen the UMIK needs to be selected as the REW input device and the input also needs to be selected, if either is left at 'Default' REW can't access the volume control. REW usually deals with that automatically when it first detects the UMIK.


----------



## oweee (Apr 2, 2015)

JohnM, yes the input volume control it controls the mac os system mic input level. For instance if I go into the macbook pro's Sound preferences and set the UMIK input level & then go to REW & load the calibration file the level that I set in system prefs does not change so how does REW get an accurate SPL reading? AM I missing something obvious?...


----------



## JohnM (Apr 11, 2006)

As above, REW reads the volume control setting and takes into account the effect it has on the UMIK's internal gain setting.


----------

