Very high SPL in "silent" room with Umik-1?

[tobiasga]

Hi,

I just got a UMIK-1 microphone as I wanted to experiment with REW. I have it connected to my HTPC, running Windows 10, which is connected to my receiver (Denon 4520) over HDMI.

I followed the instructions on minidsp.com (minidsp.com/applications/acoustic-measurements/206-umik-1-asio4all)

However, when I open the REW SPL meter, with no audio playing, I get a reading of around 85 dB. That can't be right?

I noticed that the microphone appears in Asio4all with this name: Umik-1 Gain: 18dB, whereas in the guide its 0dB (minidsp.com/images/appnotes/umik-1-asio4all/umik-1-asio4all-control-panel-alt.png)

I have set the Mic level in Windows 10 to 0 dB - if I decrease this, it also decreases in REW, but I don't think I'm supposed to lower it? And I wouldn't know how much to lower it anyways.

Anyone got any idea why I get such a high reading in a 'quiet' room? I can't really continue and do measurements as I can't set the volume on my receiver to give a reading of around 75 dB with pink noise, as described in the guide.. as it's already so high

Many thanks in advance!

PS I had to remove www from the links as I'm not allowed to post links with less than 10 posts

 

[EarlK]

I'm guessing the problem is that you haven't loaded the UMIK's calibration file for that specific audio device arrangement ( iow; the ASIO4all setup that includes the UMIK-1 mic ).

New users can get easily confused ( even though the "auto-sense" window prompts, do give good guidance ) due to the need for multiple loadings of identical calibration files for their test mics ( since it's no longer a global setting ["set-once"] but instead is a device-specific setting ).

 

[tobiasga]

In addition I just had a look at the dip switches inside, and they are set so its gain 18.

Furthermore the sensitivity factor is -39.88 dB in the calibration file.

 

[tobiasga]

Hi EarlK,

Thanks for your reply! I do have a calibration file specified in Preferences > Cal Files in the "Mic cal files" section under ASIO4ALL v2.

In the "Soundcard cal files" section I dont have anything specified.

Is that not correct/enough?

 

[EarlK]

Hi EarlK,

Thanks for your reply! I do have a calibration file specified in Preferences > Cal Files in the "Mic cal files" section under ASIO4ALL v2.

In the "Soundcard cal files" section I dont have anything specified.

Is that not correct/enough?

Hi,

What you've done is correct.

You might want to open up the RTA window ( within REW ) and have a look-see.

Perhaps there actually is a loud ( but inaudible ) frequency skewing the results seen in REW's SPL meter window.

After that, I'm out of ideas.

 

[tobiasga]

Hi again,

The RTA window looks like this - seems like its all over the place? Im sitting in a basement room and it is indeed quiet.. and im not deaf

 

[EarlK]

That looks normal to these eyes ( the black trace in frequencies above 100hz )..

There's typically more LF "noise" in a real time setting ( & even more so, in some basements due to proximity to HVAC parts ).

 

[tobiasga]

How do I set correct volume on my receiver then for taking measurements? Guides say to aim for 75 dB, but the "silent" reading is already higher then that? As soon as there's just a little bit of noise in the room (like normal talking), or even some upstairs it goes above 100 dB.

And there is no HVAC parts in this basement..

 

[John Mulcahy]

Furthermore the sensitivity factor is -39.88 dB in the calibration file.

That would be pretty unusual. What is the serial number of your UMIK?

 

[tobiasga]

Hi John,

The serial number is 708-0037

I downloaded the file from:

UMIK-1

The UMIK-1 is an omni-directional USB measurement calibrated microphone providing Plug & Play acoustic measurement. From speaker & room acoustic measurement to recording, this microphone provides low noise and accurate results you can rely on.

www.minidsp.com

It's the same sensitivity factor in both calibration files (90 degrees and regular)

 

[tobiasga]

For what it's worth, I noticed a date stamped on the PCB: Jan 10, 2018 - and above that "ver 1.6".

 

[John Mulcahy]

A more typical figure would be around 4 dB. I suggest you raise a support ticket with miniDSP to query it, I'll also send them an email.

 

[tobiasga]

I will do so, thank you very much!

 

[John Mulcahy]

Looks like there was an error in processing some calibration files that has since been corrected, if you download the cal files again they will have the correct sensitivity figure.

 

[tobiasga]

I got the same reply from them in my ticket, thank you! The new calibration file got a sensitivity of -2.88dB, now I get a reading of around 52 dB - does that appear correct to you? In the room I just have my projector on (which is subjectively pretty quiet).

 

[John Mulcahy]

It's about right. In a very quiet environment the SPL figures can be in the 40's. From your original plot there look to be some mains hum and perhaps fan-related components at low frequencies, the C and A-weighted SPL figures are lower as they place less weight on those low frequencies.