Polarity anomaly - UMIK-1 vs. UMIK-2

[AustinJerry]

Was the 2/24/2023 measurement done with the Java driver and EXCL device?

No, the ASIO4All driver was used. The 7/5 measurement used the Excel drivers. Do you think the driver selection would make a difference?

Did you look at the MDAT file? Something peculiar is going on with the Dirac Off/On measurements.

 

[thothsong]

Definitely worth trying the ASIO driver again, to see if the polarity changes.

What about the Dirac off vs on measurements is peculiar?

 

[AustinJerry]

Definitely worth trying the ASIO driver again, to see if the polarity changes.

What about the Dirac off vs on measurements is peculiar?

OK, I ran a fresh set of measurements using both the UMIK-1 and UMIK-2 and switched between using the Java Excel driver and the ASIO driver (MDAT attached). All of the UMIK-2 measurements using both drivers are showing negative polarity, while all of the UMIK-1 measurements are showing positive polarity. Very strange, but consistent.

Another peculiarity that I am trying to understand is the impulse alignment. While the UMIK-1 and UMIK-2 impulse responses are showing inverted polarity, I still would expect them to line up on the horizontal time scale. This is not the case, as shown here (a difference of .0995 ms.):

I am at a loss trying to understand what I am looking at here. Which mic is correct? Does it really matter for the casual measurements I am likely to make? What about a Dirac calibration--will there be a difference depending on which mic I use?

And never mind my comment about a difference between Dirac off and on--after looking at it again, I don't see an issue.

 

[thothsong]

Sorry, I don't have an explanation for the polarity or the timing difference.

 

[AustinJerry]

If you had a choice of which mic to use, which would you pick? Or does it really make a difference?

 

[thothsong]

In that old post, you showed UMIK-1 and UMIK-2 SPL measurements that were basically the same. In your most recent measurements, they're very much different. If you were careful in placing both mics in the exact same position for the most recent measurements, then it looks like an SPL change has also occurred at some point. In your most recent measurements, there's a clear and consistent difference in the 20-200 Hz range between the two mics, and significant variations at higher frequencies. If your environment and audio equipment haven't changed since the beginning of last year, then I'd try comparing current measurements with measurements from last year, UMIK-1 vs UMIK-1 and UMIK-2 vs UMIK-2, especially in the bass range which should be more consistent, to see if either mic has remained stable.

 

[AustinJerry]

Thanks for your suggestion, but for now I'm just trying to understand the polarity difference. While my equipment and environment have remained relatively stable since the "old post" and today's measurements, there could always be some variables, like slight differences in mic placements, or some slight differences in room furniture. I am hoping at some time that JohnM will weigh in on the polarity issue, but John has some personal issues he is dealing with right now. I also have the open ticket with MiniDSP, so they might have some insight.

 

[sam_adams]

The differences in the impulse timing could be linked to something as simple as processing delays in the mics themselves—different ADCs—or a slight change in the position of the mic between measurements. The difference in the timing—99,5µS—is equivalent to two wavelengths at 20KHz or 720˚ of phase. The overarching issue is one of polarity. I am most interested in what the response from MiniDSP will be regarding this issue since it seems to have gone unaddressed for a considerable length of time. @AustinJerry, you have gone the extra mile—as always— to help us understand this issue. Thank you. Now, let's see what MiniDSP has to say.

 

[thothsong]

The differences in the impulse timing could be linked to something as simple as processing delays in the mics themselves

I don't understand how that would change the timing relative to the timing reference. FWIW, I don't see a difference between my UMIK-1 and UMIK-2.

 

[sm52]

AustinJerry,​

Arrange with someone near you that you will come to him with your microphones and take measurements on his computer with both microphones. Java excl drivers, all windows enhancements disabled.