Recording hum

[newtomotu]

I am a novice recording vocals to an old project using a Rode NT1 condenser mike into a Motu 896mk3, connected to my Macbook Pro via a Usb cable (the firewire cable disconnected continually with the slightest of movement). I am using Logic Pro X. I have the mike in the first input with phantom power turned on. There is a very loud hum, which produces a large thick sound wave even before singing. I have tried trouble shooting this via various ways:
!. The same mike, stand and cable connected to a Zoom TAC1 interface via a thunderbolt cable in the same room work fine.
2. I disconnected the modem and all electrical devices from my music room, and then from the whole house, and connected the motu to another wall socket via a small extension cord and power board.
3. I moved the whole setup into another room (away from the mains power, which is on the other side of the wall of my music room).
No difference was obtained via these methods.
4. I took my whole set up to a friend's home studio, and connected it all there with his power supply. The only difference was instead of outputting via my headphones, we outputted via his external speakers. It worked fine there, with a normal sound wave.
5. Returning home, I tried again here with the same hum as before. I connected a Shure sm57A and Shure sm58 to the Motu, and they recorded fine without the hum and thick sound wave.
How can I resolve the loud hum and thick sound wave from this condenser mike connected to the Motu 896mk3?
Many thanks!!

[Phil O]

As I read your post I thought I knew what was going on, then I'd read the next thing you tried and got stumped again.

It doesn't sound like a power source problem (your electric supply) but it worked at your friend's studio. Hmm.

The Rode uses phantom power and the Shures do not, suggesting that the problem might have to do with the phantom power in the 896 - but again it worked at your friend's studio. Hmm.

It works with your TAC1 suggesting that the Rode and cable are OK.

There were TWO things that changed at your friends studio, power source and audio output. Have you tried the output setup (i.e., output to speakers vs headphone outs) at your location?

Also, do you have a way to check the integrity of the ground at your location?

Just throwing out ideas here, guy.

Phil

[newtomotu]

Thanks Phil,

I don't have any studio monitors (just some regular jbl's), so haven't tried connecting speakers here. (The only reason that I didn't try the headphones at my friend's studio is because my headphone adapter broke!! I've since got a new one, and the problem remains.)

I'm at a rental property, and asked the owner with regards to the integrity of the power supply. He said it was all tested before buying, but that was as much as he knew. I have some electrician friends I could ask to test the grounding when they are next in town, but none of them are around at the moment...

It is frustrating!!!

[HCMarkus]

Look for ground loops (different paths to AC ground).

Remember that USB provides another path to ground. To free my USB-connected Yamaha Motif and S90 from ground loop-induced hum, I had to cut the ground wire within the USB cables connecting them to my Mac. You could try this approach; it could possibly solve your problem.

Also, try testing/replacing cables. Intermittent issues can be a bugger to find and fix.

[MIDI Life Crisis]

You can test the basic grounding with a $5 device from an electric/hardware store. I keep one in my travel gear for iffy connections.

I'm totally w/o suggestions as to the problem. Have you tried a different phantom powered mic?

[newtomotu]

Thank you everyone for your suggestions... The strange thing is, after trying one more time today before heading out to get a ground tester.... I found everything is working fine!! I checked, disconnected and reconnected cable connections several times over the past few days, so can't imagine it was that. Mysteriouser and mysteriouser... anyway, it is working so I am going to start recording. Thanks again.

[mikehalloran]

There are some very old threads on this. Search for USB hum. I'm out of town on my phone. Often the solution is to cut the sheild at one end to get rid of that ground loop.

Saying the cables are great doesn’t matter. Sometimes you have to modify a cable to accomplish the task at hand.

You clearly have a ground loop that must be broken.

[newtomotu]

Thanks Mike,
I searched the thread without luck, but googled info. I'm pretty ignorant when it comes to electricity, but understand now what the ground loop is. My remaining question is: can a ground loop come and go (in the same setup)? Also, while I thought I was using my laptop some of the time without being plugged in, maybe I am wrong. Would running it on battery power eliminate the problem? (I definitely had the laptop plugged in today when I was experiencing no problems). Or is the condenser mike another part of the ground loop issue?

[stubbsonic]

Sometimes the orientation of a cord or device near the power supply of another device can induce hum.

[HCMarkus]

Possibly an intermittent shorted cable or loose or dirty contact.

Also: Exercise is often good for humans and audio potentiometers and connectors.

[mikehalloran]

Thanks Mike,
I searched the thread without luck, but googled info. I'm pretty ignorant when it comes to electricity, but understand now what the ground loop is. My remaining question is: can a ground loop come and go (in the same setup)? Also, while I thought I was using my laptop some of the time without being plugged in, maybe I am wrong. Would running it on battery power eliminate the problem? (I definitely had the laptop plugged in today when I was experiencing no problems). Or is the condenser mike another part of the ground loop issue?

Yes. Goes away when the laptop is on battery ... a clue or red herring. What else is different?

It can be induction but moving cables and connected devices should change the intensity. If not, suspect a loop.

My place has wiring from 1960 with no grounding. I went to star-quad cables to eliminate induction noise across the spectrum.

I was looking at spending the money on balanced power but knew it couldn’t eliminate a lot of the noise and that ground loops weren’t my problem.

Balanced power is expensive and if any of your devices are wired incorrectly, it can kill you. It absolutely elinates 60 Hz hum.

[newtomotu]

Thanks you again everyone for all of your advice and suggestions. Every time I step into the studio (infrequently, but hopefully more and more from now on!), it is a massive learning curve. Maybe it was the cord positions/crossing, or dirty, loose or un-exercised connector! Hopefully if the issue re-occurs, I won't have to spend days trying to trouble shoot again. In the meantime, I'll take on board suggestions and learnt info re: checking for grounding and solutions. Had a problem-free 3 hour block in the studio yesterday without issues, so presently smiling!!

[Phil O]

Now that we know the problem is intermittent I would lean towards faulty cable or connector (but that's still not definite). I think ground loop COULD be the problem but I doubt it. Changing from a phantom power mic to a dynamic wouldn't change the grounding configuration, but it would change how the wires are used in the cable. A dynamic mic can still work with the ground wire disconnected on an XLR cable (not well but can still work), but phantom power depends on that wire. I should have thought of that before .

For those interested the basic circuit is here:
https://www.sweetwater.com/insync/how-p ... wer-works/

If you experience the problem again, the first thing I'd do is swap mic cables and see what that does.

Phil

[MIDI Life Crisis]

I'm guessing (after reading this thread) it is probably a USB device or cable inducing "hum" caused by the data stream. I'd disconnect all possible USB devices when the hum is there. I suspect the culprit will be found that way.

[newtomotu]

Roger that!