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Discussion Starter #1
Hey guys just doing some measuring today and I accidentally did a sweep with mute on and to my surprise saw a pretty big spike at 60hz which I've always thought was my room. I assume it has something to do with electric equipment running at 120V/60HZ but my question is do I just assume that and assume it's close to what my graph shows before 50 and after 70 HZ or is there a way to run a background sweep and filter that sweep from my real sweeps? Here's the graph to show what I'm talking about.
 

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Sometimes you can avoid issues like that and also help the noise floor by using a non-USB mic with phantom power.
I use a Cross Spectrum EMM-6 with a Behringer XENX Q502USB for external DAC and phantom power.

It also might help to use a line conditioner.
 

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It's the dreaded 60hz ground-loop hum.

With nothing running through your system, crank up the volume. Does it hum??
 

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You must be able to hear that before you even measure. Is this a constant occurrence? I'd address that first.


Are you utilizing a laptop that is plugged in to an outlet? Try running on battery while measuring.
Connected via RCA cables to the AVR? Is HDMI an option?
 

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Discussion Starter #7
Alright to address the latest questions, I actually don't hear anything when everything is turned off or electronics on mute, etc. I'm measuring on a desktop that's plugged into an outlet but I can use my laptop without being plugged in if it might help. Also I'm plugged into an ungrounded outlet at the moment (old house) but I'm having a grounded one put in next week so maybe that will help I don't know. And finally here is a plot of background noise using the RTA record in REW which I have no idea how it's different than the normal measure function but I'll look into it. And I'm using a Umik USB microphone and HDMI from my desktop to processor.
 

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Discussion Starter #9
Thanks guys, looks like I have some work to do solving it but at least I know what the problem is now.
 

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Discussion Starter #10
I started thinking about this more and don't think it's a ground loop hum because I don't hear anything when no source is playing and it should be a pretty loud buzzing based on the graph. So I installed REW on my laptop and redid the RTA analyzer and the 60hz peak was still there but not as high and then I unplugged my power cord from the laptop and it went away entirely, so I guess I'll just have to start doing my measuring like that and all should be well. Thanks for everyone's help
 

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I think your UMIK might be broken/defective. It happens.

You'd definitely notice a 90db 60hz tone. LOL!

You could open it up and take a look, probably one of the three wires inside have come loose.
If you have a soldering iron you might be able to fix it, but it might be easier to just get a new one.
http://www.avsforum.com/forum/155-diy-speakers-subs/1797489-massively-clipped-umik-1-a.html

Buy one from CSL, theirs are at least inspected for quality before it is shipped out!
http://cross-spectrum.com/measurement/calibrated_umik.html
 

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Well to spite the seemingly all digital USB path here, the mic still has an analog front end (preamp and AtoD converter), and this is powered from the computer's +5v USB power. It is not uncommon for computer switch mode power supplies to contain a significant amount of 60hz EMI/RFI noise on the output voltages from the primary side of the power supply.

This can easily be amplified by the sensitive low level mic preamp chip inside the UMIK.
 

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Discussion Starter #15
I didn't see that part. Doh!
I guess I spoke too soon cause next time I did some measuring even with the laptop unplugged it was back. I'm getting my new outlet installed this week that will be dedicated to my home theater equipment so I'll report back if that fixes the issue. I also ordered an APC surge protector that is supposed to filter out noise pretty well so I'll see what happens.
 

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I guess I spoke too soon cause next time I did some measuring even with the laptop unplugged it was back. I'm getting my new outlet installed this week that will be dedicated to my home theater equipment so I'll report back if that fixes the issue. I also ordered an APC surge protector that is supposed to filter out noise pretty well so I'll see what happens.
Now this isn't making sense at all.

Just to be clear, is the UMIK the only device attached to the laptop? That means the ONLY external device, including power supplies and any audio cables to your AV gear?

Because if that's the case, the 60hz is either airborne acoustical noise or a strong EMI field. If you take the laptop and UMIK to another room or location, do you still get the 60hz peak?

Replacing the outlet is not going to make any difference in this case because you have already proven it's not coming from the power line.
 

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Discussion Starter #17
Now this isn't making sense at all.

Just to be clear, is the UMIK the only device attached to the laptop? That means the ONLY external device, including power supplies and any audio cables to your AV gear?

Because if that's the case, the 60hz is either airborne acoustical noise or a strong EMI field. If you take the laptop and UMIK to another room or location, do you still get the 60hz peak?

Replacing the outlet is not going to make any difference in this case because you have already proven it's not coming from the power line.
When I originally measured my RTA noise I didn't have anything else hooked in to the laptop but when I was actually running sweeps I had the HDMI going into my receiver so that could have still been picking up some noise.
 

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When I originally measured my RTA noise I didn't have anything else hooked in to the laptop but when I was actually running sweeps I had the HDMI going into my receiver so that could have still been picking up some noise.
Ok yes, the HDMI cable could couple 60hz trash back to the UMIK preamp through the ground wires.
 

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Discussion Starter #19
Well I now have a completely separate circuit that runs all of my home theater equipment and bought a new APC surge protector that is supposed to have good noise filtering abilities and I'm still seeing the same 60hz peak. I'm at a loss because even with my laptop now with nothing hooked to any wall outlet or HDMI hooked to the receiver I'm still seeing it. You would think I'd be hearing a loud 60hz buzzing or something but I don't so either the mic is messed up or it's just picking up some low level buzz and messing with my readings.
 
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