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UMIK-1 High Ambient SPL Measurements in REW?

Alamei

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I recently purchased a UMIK-1 to use with REW for calibrating speakers, and I ran into a question when I was performing initial checks in REW: When I open the SPL meter and let it log sound without playing anything (just recording background ambient sound, no pink noise or anything of that sort), it shows a baseline level of ~70dB (see attached image for reference). The only background noise in the room is generated by some quiet computer fans, and I've previously measured the ambient sound level in my room with a cheap SPL meter to be in the 40dB range. Am I misunderstanding what that meter in REW is meant to show or using settings wrong? The only thing I did within REW was apply the MiniDSP calibration file to the mic input. My room obviously does not have 70dB of background noise, or I wouldn't be able to think straight, so I figure something else peculiar must be going on with the measurements.
 

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Blumlein 88

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You need to show us the spectrum. You may have some low frequency noise that you don't hear, but would make it read at a high level. Though that level does look much too high.
 

HarmonicTHD

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You need to enter the mic sensitivity correctly. Don’t remember the exact expression, but the value is about 0.5 if I remember correctly. Better show a screenshot of you Setup tabs.
 
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Alamei

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Huh... I think it may have to do with the calibration file. I'm attaching a sample spectrum measured (again no sound playing) with the calibration file applied (red) and using the default input in REW that doesn't apply calibration (blue), and the latter numbers (peaks in the 40-45 dB range) seem far more believable to me. I'm also including a picture of my settings page.
 

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Blumlein 88

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The Umik cal file should have a gain setting applied. I think mine is -18 db.
 
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Alamei

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Never mind me. It appears I broke something in the settings the first time I opened REW without having any clue what I did. I just tried the "delete all preferences" option to start from scratch, then let REW re-detect the microphone and re-apply the calibration file when it asked, and now everything is reading properly with the calibration applied as well as without. It looks like I somehow managed to get a flat 30dB gain applied to the measurements when calibrated when I loaded it in the first time?
 

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edechamps

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Another trap to watch out for is the Windows microphone level, which can end up affecting measurement gain, depending on which audio I/O method you use in REW. When you plug in the UMIK-1 the Windows audio input device level should set itself to the correct 0 dB (neutral) gain by default, but it's easy to change it by accident or because some other app somewhere decided to mess with it behind your back.
 
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Alamei

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Good to know. I'm assuming that's what the "control input volume" setting in REW that pins the volume to 0.54 is designed to fix?
 

staticV3

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@Alamei you can use Java EXCL input in REW to completely bypass the Windows microphone level for the UMIK and get reliable readings, within the UMIK's capabilities.
 

JohnPM

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Good to know. I'm assuming that's what the "control input volume" setting in REW that pins the volume to 0.54 is designed to fix?
Not really, but since the UMIK's level controls are in the digital domain it doesn't really make sense to use anything other than 0 dB. If you right click on the volume control on the Levels tab of the Windows Audio Properties for the input you can have it read in dB.

REW generally manages to work out whether a volume control correction is needed for the mic, which depends on the driver type and the mic serial number. There was a batch of mics that didn't follow the pattern, but those should be correctly handled in the current 5.20.14 early access build.
 

RayDunzl

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The volume control on REW with my UMIK-1 apparently adjusts the dBFS level, turn it up and the maximum testable SPL decreases, turn it down, and the maximum testable SPL increases.

In either case, the SPL that it registers for a sound of the same level remains the same. It gives or takes headroom, as it adjusts and recalibrates for the volume control setting.

Volume all the way down, have 85dB headroom on the dBFS scale:

Little red dot on the scale follows peaks...

1679257831208.png


Volume all the way up, only 35dB headroom on the dBFS scale.

In both cases the displayed SPL on the meter (TV in background) is the same at about 55dB SPL.

1679257989927.png
 
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Alamei

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If you right click on the volume control on the Levels tab of the Windows Audio Properties for the input you can have it read in dB.
That's super useful! Why on earth would they hide that setting behind a right click on the type of control that you would traditionally never right click?!
 

kolestonin

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Another trap to watch out for is the Windows microphone level, which can end up affecting measurement gain, depending on which audio I/O method you use in REW. When you plug in the UMIK-1 the Windows audio input device level should set itself to the correct 0 dB (neutral) gain by default, but it's easy to change it by accident or because some other app somewhere decided to mess with it behind your back.
Not really, but since the UMIK's level controls are in the digital domain it doesn't really make sense to use anything other than 0 dB. If you right click on the volume control on the Levels tab of the Windows Audio Properties for the input you can have it read in dB.
Seeking for help as it seems I face a weird issue in being unable to set the level to 0db no matter what I try.
I can right click and toggle between percentage and decibel.
Percentage goes up and down 52, 53, 54 in steps of 1.
But decibel steps up and down in 0.3 steps.
53 is -0.2db and 54 is +0.1db.
Tried to place my cursor on the text field so to change it manually but it accept no input.

I plugged the microphone to my work laptop so to check it.
It was correctly set to 0.0db by default.
But once I changed the setting, putting it back to 0 was again impossible. And db goes up/down in 0.3 increments.

It seems I have a defective unit?
Is there anything else I could try windows wise?
 

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staticV3

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@kolestonin You could use REW's new Java EXCL input.
That'll bypass the Sound Control Panel and use the UMIK's raw output, so that the Windows volume no longer matters.
 

JohnPM

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Seeking for help as it seems I face a weird issue in being unable to set the level to 0db no matter what I try.
I can right click and toggle between percentage and decibel.
Percentage goes up and down 52, 53, 54 in steps of 1.
But decibel steps up and down in 0.3 steps.
53 is -0.2db and 54 is +0.1db.
That's completely normal. Windows uses the whole percentage figures as the reference and shows equivalent dB figures for each step. Either of those is fine to use.
 

kolestonin

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@kolestonin You could use REW's new Java EXCL input.
That'll bypass the Sound Control Panel and use the UMIK's raw output, so that the Windows volume no longer matters.
that covers also another question I had as a REW noob:)

as I wasn't sure if using(as I do) the EXCL output&input is the correct way to go
 

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