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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #23984

  • tecnogadget
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Im having this weird issue, i dont know why but the Umik is showing a massive sustained peak at 50hz and 150hz
I've attached a capture of a Waterfall, measurement made in complete silence with no sound output at all. Acoustically treated room with good noise floor. As you can see, in the Waterfall plot, both peaks could be mistaken for room modals since they do not decay at all...but it can't be since the measurement was made in complete silence.




Why is this happening? I live in South America, we use 50hz and 220v...could that be the issue? Because it is messing up all my Subwoofer calibration measurements....tricking me into thinking i was having a 50hz decay problem even having lots of basstraps.
And it does not make sense at all since the peak is almost 80db ?¿ how could that happend in complete silence ?
Sensitivity issue? Noise floor ?

Could please somebody help me trooubleshoot this?
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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #23985

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First off, does it work as a microphone - what do you get if you have an actual acoustic signal?

Second, are you using a laptop and if so, what happens if you disconnect the power supply?

Use the RTA screen for this type of measurement.
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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #23986

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Yes it works as a microphone. Been doing measurements all day long since yesterday...but something looked suspicious....that 50hz peak could not be that bad, i though it was room modal ringing....but my brother though it was suspicious too and told me to measure in plain silence.

I was using a desktop slim computer with HDMI out. I've just changed to a macbook with battery 10min ago in order to troubleshoot the issue...and the same problem persists.

Here is a RTA screenshot from the desktop pc




And here some RTA screenshot from the Macbook Laptop (battery only)







And here an actual Subwoofer only measurement







Is it the UMIK 1 malfunctioning?
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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #23987

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Here is another subwoofer measurement...you can apreciate how those 50hz and 150hz peaks keeps ringing...
But again, i made measurements in complete silence and those 2 peaks still shows up ! So they are messing the real measurement.
Should i trust the data from the UMIK? Im totally disapointed, this should be a professional product. I can´t get serious performance if i cant know with exactitude what is happening in the waterfall plot at 50hz and 150hz since the measurement looks contaminated.


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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #23989

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When you're done complaining, disconnect the laptop from the audio system. What do you get then?
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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #23995

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Yes, i already though about power transformers, power supply causing it...but they are not. I've done the same measurement with Umik conected to Laptop and no conection to audio receiver...those peaks still there.

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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #23997

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Is there any machinery running nearby e.g. a refrigerator, air conditioning, anything like that? (FWIW I sometimes resort to pulling the fridge out so I can unplug it - and that's in the next room.) And you have put your ear to the speaker and there is no hum?

I'd be inclined to try using the internal mic in the laptop and see what that picks up. If it shows signs at 50 and 150 Hz, then it's either in the air or the laptop. If there's nothing at all, then I guess it would have to be the UMIK... although it does seem odd that it would generate 50 Hz...

The other thing I would do is try a different cable, in case there's a bad connection ...

If none of that shows a culprit, then the UMIK seems to be the only thing left...
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-> Have you read the User Manual??
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-> Have you posted a screenshot?
-> Have you posted your config file?

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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #23999

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Thanks for your concern John. The measurements are made in a mastering room, so its acoustically treated and isolated. Air conditioning turned off, no machinery nearby. I 've even tried with the audio amplifier turned off so no sound or hum is coming from the speakers.
Even tried a better cable with RFI filters in both ends and those peeks still there. Tried the Laptop internal mic and they don't show up.

My UMIK serial number is 701-1968 , and the calibration file says "Sens Factor =-1.094dB, SERNO: 7011968"

Measurements where made with -12dbs Sweep, with 15db / 7db headroom. Volume in the AVR usually -20db -15db

Could it be a calibration file issue or sensitivity issue? I've been following REW 101 v4.5 guide, i got all settings right. I just don't get why i get those 50hz and 150hz peaks.

Im in the stage of Subwoofer room calibration with the DSP1142p, and i can't tell for sure if when i apply the EQ filters the frequencies near 50hz and 150hz decay at a good rate since i got this problem. It leave me bass blind.

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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #24000

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Try taking the measurement again with the lights turned off. My bet is that you have fluorescent lights and the magnetic ballasts are giving off EMI that is being picked up by the condenser mic. The 50Hz is probably the signal given off by the primary coil and the other frequencies are probably the secondary coil. If this were ground noise then they would be even harmonics of each other (50Hz, 100Hz and 200Hz). However these are odd harmonics which are probably different windings of a magnetic transformer. Your laptop mic is not picking it up because either it is not using a condenser microphone or the casing is providing an adequate EMI shield. You can fix this permanently by switching over to electronic ballasts.
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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #24098

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Some good suggestion/questions already from John and Sly. From our side, we've never seen anything similar before so we're going to need more info on your setup to help I think..
- You're not holding the microphone with the hand we guess?
- Sounds like a ground loop somehow but of all the mics we've got worldwide we've never seen this. Not sure why it's showing up here..
Please tell us more of your setup (Eg.. take some pics). Is this a laptop, is this a PC, are all devices grounded (earthed), is the cable the one provided?

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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #24165

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You were right, that was the reason. I switched the lights off and the peak diminished by 5-10db, this helped me to carry on with the measurements. With that 50hz peak at only 50-55dB with the lights off, i made the subwoofer measurements at 100dB or more, that gave me 45dB of headroom and allowed me to verify the decay times properly.
Thanks a lot !
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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #24166

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Dear Devteam, i'll try to test the microphone outside the house with RTA just to verify if that 50hz peak disappears 100%.
As i mentioned before Sly was right and it seems the issue was caused by the magnetic ballasts EMI.
Measurements were made with Desktop Pc (earthed) and with Laptop (battery). And you guess is right, wasn't holding it with my hands(thats for cavemans haha )
When i was troubleshooting the issue i used both the cable provided and another one i own which has Ferrite filters in both ends.
Switching the lights off was the only thing that helped taming the 50hz peak.

I hope this helps someone with the same issue in the near future. Cheers !







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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #24227

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Thanks for the feedback Tecnogadget. Good find from Sly too! Never seen this before here.. We learn everyday is the beauty of our community! :-)

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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #24408

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I get random 38hz spike, found out it was my fridge upstairs. When it runs, it creates the spike. It's gone when off.

I get another small spike at 115hz.
Found that to be my desktop computer.
Verified by connecting to laptop, having laptop as far as possible, around a corner.
It(115hz spike) is there when desktop on, gone when desktop off.
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Umik 1 50hz humm/peak with silent measurement 5 years 6 months ago #24416

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Interesting, thanks :)
I am not miniDSP support.

"You must ask the right questions." - Dr. Alfred Lanning's hologram.
-> Have you read the User Manual??
-> Have you drawn and posted a diagram?
-> Have you posted a screenshot?
-> Have you posted your config file?
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