Different results on the same measurement

[funnyname]

Hello,

I get different results on the same measurements in REW.

REW1

• funnyname
• Jul 6, 2017

measurement drift

In the picture you can see three graphs. These measurements are all taken with the same level calibration and the same settings. The MIC and speaker stayed at exactly the same place. All the measurements are gated with a 3 ms IR Window.

I have checked the log file, I don't see any problems there:
jul 06, 2017 1:52:35 PM roomeqwizard.RoomEQ_Wizard main
INFO: REW V5,19 Beta 6 running JRE 1.8.0_111 32-bit on Windows 10
jul 06, 2017 1:52:38 PM com.synthbot.jasiohost.AsioDriver <clinit>
INFO: Loaded jasiohost.dll
jul 06, 2017 1:52:38 PM roomeqwizard.CalData calFileLoader
INFO: Mic sensitivity -0,216 dB

I use the UMIK-1 from miniDSP and the Topping A30/D30 amp/dac combo. I have also used an Audinst HUD mini, with the same outcome.

Do you have any idea what could be the problem here? I can't trust the measurements now, so how can I start creating a filter..
Manny thanks in advance for the replys.

Cheers.

 

[John Mulcahy]

Are you using multiple sweeps? Need to use single sweeps with a USB mic (or more generally when the input and output are on separate devices).

 

[funnyname]

Yes I indeed use multiple sweeps (I thought that would give a better result)
I will test what happens when I use single sweeps, great TIP.
Thanks

 

[funnyname]

Ok I can confirm this was the problem. Now if I takes measurements in one sweep, the curve stays almost the same, but not identical.
One little extra question, because I use a USB MIC and sound card, I can't calibrate those two in REW. I assume this is not a problem because the MIC is calibrated by file. But still, the sound card is not. Am I missing a step here, or is this just the way it works?

Thanks again, I am glad this problem was solved.

 

[John Mulcahy]

No, not missing anything, no soundcard cal with USB mics.

 

[funnyname]

OK thanks again. Excellent response here, better than some commercial companies.
That reminds me, I still have to donate REW, going to do that right now!

 

[John Mulcahy]

Thank you!

 

[Sonnie]

Yep... have you ever seen anyone who puts so much of his time into such an extensive project that is as superb as it is... all for free... or the occasional donation?

And there are those out there that try to sell inferior products for hundreds.