Getting different SPL numbers on the Mac and PC with same calibrated UMM-6..what's happening?

[slicksilver79]

On the PC (Windows 10 up to date) - https://imgur.com/a/lbOVZwC

On my Mac - https://imgur.com/a/VfXpOOV

Can someone throw light on why there is a huge difference? Settings are the same and the same calibrated file was used. Almost a 20db difference .

 

[John Mulcahy]

The input hasn't been selected on the Mac, still showing "Default input". That means REW can't access the input volume setting to take it into account.

 

[slicksilver79]

Thank you! That did the trick.

 

[slicksilver79]

Thank you! That did the trick.

Oops! Spoke too soon. I selected the right input on the mac and now the difference is about 7-8db. Earlier it was close to 20 plus. This is how my sound card preferences look like - https://imgur.com/a/fPgJm5m. Anything else I'm doing wrong? Thanks again for your help.

 

[John Mulcahy]

The relationship between the input volume control and the mic gain may not be what REW thinks it is on either the Mac or the PC (or possibly both). To check that, play a test signal (e.g. pink PN) at a comfortable level then keep an eye on the SPL meter reading while trying a few different input volume settings. If the meter goes back to the same value after the input volume is changed then the correction is working as it should, if not a bit more investigation will be needed to establish what the volume-to-mic-gain relationship is.

 

[slicksilver79]

Pardon me as I'm new to this - Where can I try different input volume settings? Also, is the test signal part of REW and how would you determine comfortable level. Appreciate your help in trying to help me out!

 

[John Mulcahy]

On Windows there is an input volume setting just under the input selection on the REW soundcard preferences, you can change it there. On Mac you will need to use the Mac's sound settings. For the test signal use REW's signal generator and play the pink noise signal using the "Speaker cal" setting, assuming you are connected to a speaker somewhere in the system. By "comfortable level" I mean something you could happily listen to for a long period, not loud, say 70 dB or so.

 

[slicksilver79]

On Windows there is an input volume setting just under the input selection on the REW soundcard preferences, you can change it there. On Mac you will need to use the Mac's sound settings. For the test signal use REW's signal generator and play the pink noise signal using the "Speaker cal" setting, assuming you are connected to a speaker somewhere in the system. By "comfortable level" I mean something you could happily listen to for a long period, not loud, say 70 dB or so.

Thank you for this John. This made it so much easier.

The relationship between the input volume control and the mic gain may not be what REW thinks it is on either the Mac or the PC (or possibly both). To check that, play a test signal (e.g. pink PN) at a comfortable level then keep an eye on the SPL meter reading while trying a few different input volume settings. If the meter goes back to the same value after the input volume is changed then the correction is working as it should, if not a bit more investigation will be needed to establish what the volume-to-mic-gain relationship is.

On the Mac for different input volume settings I'm getting different SPL numbers - https://imgur.com/a/TdIPKGh. On Windows, different input volume settings in the same and constant SPL number. Would you say the windows SPL number is more/most likely the closest accurate reading? At this point not concerned of the numbers matching on the different OSes/hardware..

 

[John Mulcahy]

If they stay pretty much the same on Windows then REW is making the correct translation from input volume to mic gain, so use that. The Mac must be applying a different volume translation. If you have a little spare time one day it would be great to get some figures for the Mac volume mapping. They are easy to collect, don't need to generate any test signals. Just connect the mic to the Mac, run Audio Midi Setup from Applications -> Utilities and you will see both the volume figure (labelled Value, covering 0 to 1) and the dB gain figure. If you could give me the dB figures for a range of volume values including 0 and 1 that would be really helpful to get the Mac mapping corrected.

Here is how Audio Midi Setup looks with a UMIK connected as an example, volume is set to 0.318 and gain is 0.0 dB.
.

 

[slicksilver79]

Most definitely John. Thanks for all your help! I'll report back in 12 hours.

 

[slicksilver79]

There you go

 

[John Mulcahy]

Thanks, but I need the figures for a range of values, including the dB figure when the value is zero and the dB figure when the value is 1.0. With those and some of the values in between (like the 0.25 / 5 dB you posted) I should be able to figure out the relationship.