Has my UMIK-2 gone bad?

[AustinJerry]

I typically measure the impulse response of my left and right speakers after running a fresh Dirac calibration to make sure alignment is proper. Using the same Dirac calibration with the mic positioned in the MLP, I get very different readings depending on whether I am measuring with a UMIK-1 or a UMIK-2. Both are using CSL calibration files. The UMIK-1 measurement is what I would expect to see. I don't recall seeing these differences between the two mics in the past, so I am wondering whether the UMIK-2 is now defective, or whether there is some setting that I am overlooking.

 

[John Mulcahy]

Looks pretty odd. Can you post the mdat file for the measurements?

 

[AustinJerry]

Thanks for offering to look at the MDAT file. I re-ran the measurements again today, comparing the results for the UMIK-1 and the UMIK-2. The new measurements exhibit the impulse response issue as well. Something new, this go-around I kept getting an error when using the UMIK-2:

I am not sure how to clear this error, or whether it is contributing to the UMIK-2 impulse response issue. The UMIK-2 is set to 96 KHz sample rate, with a 1M sweep length, while the UMIK-1 is set to 48 KHz and 256K.

 

[John Mulcahy]

I am not sure how to clear this error, or whether it is contributing to the UMIK-2 impulse response issue.

You can't clear it and it isn't affecting the result. It is indicating that the timing signals are not where they should be given the sweep length and sample rate. You could try 48 kHz to see if it is any different, but something is going wrong with the clock rate somewhere.

 

[AustinJerry]

I come hat in hand to apologize for not trying one of the most basic trouble-shooting steps--using a different USB cable. I typically have a short HDMI cable from the laptop to the processor, and a 15-ft USB cable to the mic. I located a long HDMI cable and used a different, shorter USB cable to the UMIK-2, and the measurements appear normal.

Needless to say, I appreciate your responses, John, and I am off to order a new 15-ft USB cable right now. I am relieved that the UMIK-2 seems to be functioning properly.

 

[John Mulcahy]

Glad you figured it out. High sample rates and long USB cables aren't a happy combination.

 

[AustinJerry]

OK, I have received the replacement USB cable for the UMIK-2, and it seems to have resolved the anomalies I reported earlier.

However, there is a new issue that I can't figure out, possibly a setting somewhere. I measured the front left and right speakers using first the UMIK-2 and then the UMIK-1, all other things being equal. When viewing the impulse response overlay, the two sets of measurements seem to have the opposite polarity, as shown below. Any hint as to what may be causing this?

 

[John Mulcahy]

Can you attach the mdat file?

 

[AustinJerry]

Sure. Thanks for looking.

 

[John Mulcahy]

All looks fine in the setup, how do the UMIK-2 responses look at 48 kHz?

 

[AustinJerry]

I have not run any measurements with the UMIK-2 at 48KHz. I'll run some tomorrow and report back.

BTW, I have been measuring at 96KHz with the UMIK-2 since I purchased it several years ago and have never seen this issue before. The new cable is 15ft--could the cable be the issue? I'll run some measurements tomorrow using a shorter cable as well.

 

[AustinJerry]

OK, I have conducted four new sets of measurements:

- UMIK-2 @96kHz with 16-ft cable
- UMIK-2 @48kHz with 16-ft cable
- UMIK-2 @48kHz with 6-ft cable
- UMIK-1

As shown below, each of the UMIK-2 measurements are showing opposite polarity to the UMIK-1 measurement. Still no clue as to why this is happening. Any insights? I will open a case with MiniDSP support to get their opinion.

 

[John Mulcahy]

No idea, sorry. I get the same polarity from UMIK-1 and UMIK-2 in my measurements.

 

[thothsong]

I also get the same polarity from UMIK-1 and UMIK-2, with 6-ft extension cable.

 

[sam_adams]

As shown below, each of the UMIK-2 measurements are showing opposite polarity to the UMIK-1 measurement. Still no clue as to why this is happening. Any insights? I will open a case with MiniDSP support to get their opinion.

The USB cable would have no effect on the signal polarity since it is only transferring digital data. In order for the polarity to change, there would have to be a change in the analog section of the mic itself—or a possible fault in the mic's internal ADC.

 

[sm52]

I measure via ASIO driver with an external sound card. But once I was playing with measurements through the Java driver. Sony vaio laptop. If I chose devices with EXLC, there was a polarity reversal. What should have had a positive impulse gave a negative one. If I chose the same title without EXCL, all measurements were correct.

 

[AustinJerry]

The USB cable would have no effect on the signal polarity since it is only transferring digital data. In order for the polarity to change, there would have to be a change in the analog section of the mic itself—or a possible fault in the mic's internal ADC.

So you are saying that the mic is now likely defective? I have stopped using it because I no longer have confidence that it is working properly.

 

[sam_adams]

So you are saying that the mic is now likely defective? I have stopped using it because I no longer have confidence that it is working properly.

One would suppose that a hardware failure of the ADC in the mic would produce more than just a simple signal inversion error. If the ADC was bad, I would expect an all-or-nothing failure meaning no signal from the mic at all. However, being the sometimes fickle things digital chips are, it's not outside the realm of possibilities that a single bit-flip failure has occurred.

The comparison .mdat you provided was done on v5.20.13. You may want to try the latest EA release to see if there is any change in the signal polarity with the latest version. You can also try some measurements with v5.20.13 in non-EXCL mode with just the Java driver or with ASIO to see if that changes anything.

Another software-related possibility is a recent Windows update that might have mucked around with the internal Windows audio somehow. If you have another computer to test with you can see if there is any difference between them. I may be suffering from a Chat-GPT-based hallucination, but didn't you purchase a Mac recently? You could test with that to see what results you get.

 

[AustinJerry]

I appreciate your input, Sam, but I don't think the issue has anything to do with the REW release I am currently running. I have been using REW for a number of years amd have mever seen anything like what the UMIK-2 is doing. And a Windows update would likely affect both mics in the same way. And you are indeed hallucinating--I have never owned a Mac, and probably never will.

I'll report back if I figure out what is going on with the UMIK-2.