OT: audio hum from monitors

Woodenmike wrote on 12/28/2012, 4:57 PM
Since my new build, i have been going nuts trying to trace the audio hum in my studio monitors. I'm using Resolve 65a powered speakers patched through a Behringer xenyx 1204 mixer with the audio coming in from my onboard sound card (nvidea high def). My son had a similar sounding audio hum on his system and solved it by snipping off the ground lugs on his power cords, but that didn't affect mine at all, in fact it got worse. Any of you audio gurus have a process of elimination flow that i might try to narrow this down? My previous build used an EMU 0404 sound card that didn't produce any noticeable noise on that system, but this one is making me crazy!


Geoff_Wood wrote on 12/28/2012, 5:11 PM
NEVER snip the ground lugs off, unless you want to die, or be liable for your son dying.

Start by running everything off the same power strip. Do the speakers have a (legal and safe) ground-lift switch ?

Woodenmike wrote on 12/28/2012, 5:32 PM
Yes I am aware of ground safety issues, but tried one non-grounded power cord to see if that would isolate the issue before going on to other solutions. the cord as been replaced with a grounded one again. I'm not sure what a ground switch is (have never seen such labled switch on any of the speakers I've ever used in the past including our house system in our theater), but i'm pretty sure these speakers don't have them. I'll try running the audio components off the same power supply and see if that makes a difference.
musicvid10 wrote on 12/28/2012, 5:54 PM
Mute all inactive record inputs on your sound card.
Plug your little mixer into its own filtered power strip, not the same one the computer, speakers, etc. are plugged into. Try different cables from the computer to mixer, and mixer to powered speakers. Keep all the audio equipment away from your video monitor. Try it without the Behringer mixer. Try a set of headphones right from the sound card. Don't use separate wall outlets (could be on different AC legs).
ushere wrote on 12/28/2012, 7:19 PM
my experience of beringher mixers (10+ years ago) were not very complementary. i found them (i used 3 or 4 over a number of years) to be badly manufactured (cold solder connections), poor quality rotary / sliders, etc., i also noticed a level of background noise that couldn't be removed under any circumstances.

i used to use soundcraft and tascam in the studio without problem....
rraud wrote on 12/29/2012, 9:36 AM
An audio cable in close proximity to AC power transformer, (wall-wart or line-lump) can sometimes produce ground-loop like oscillations.
Power amps, mixer and soundcard/converter should be on the same electrical circuit to eliminate ground-loops.
musicvid10 wrote on 12/29/2012, 10:27 AM
The older Behringer mixer/preamps were bad, really bad.

The newer ones with "Pro" in the name are better, and quiet for their price.
Owned one of the old ones (gathering dust) but have bought three of the newer ones, including two rackmounts, and a 24 channel with efx that worked well for live sound, but just ok for recording. A band bought it from me, and they are quite happy with it.
Woodenmike wrote on 12/29/2012, 1:25 PM
thanks everyone...i will begin separating all my mains and try to figure out a plan for plugging things in that will isolate my audio devices/speakers/mixer. I will also look for another small mixer (any suggestions?) and possibly replace my speakers if all the above fails as a last resort. Thanks again to the folks on this forum for the graduate education that everyone gets here...you're all the best! Happy New Year to all!
Grazie wrote on 12/29/2012, 4:17 PM
If you've got a WiFi Modem do a simple OFF test. It was bugging me for weeks! My XLR cable from a mic was picking it up.


ushere wrote on 12/29/2012, 7:48 PM
@ musicvid - the problem with being old is i have a tendency to remember 'older' models of everything ;-)

RedEyeRob wrote on 1/1/2013, 1:24 AM
Buy this and put it in line between your sound card and mixer. It will solve the ground loop problem you mentioned and ones you don't know you have.


Most consumer level computer sound cards output audio at -10db and are unbalanced. In addition to eliminating your hum/buzz this box will convert the signal to +4db and give you a better signal to noise ratio and convert the unbalanced signal to balanced.
farss wrote on 1/1/2013, 1:44 AM
Are you sure it's even a ground loop problem, is it even strictly hum?

A lot of RFI / EMI problems sound like hum and trying to chase them down thinking they are hum can waste a lot time.
I've traced one very similar problem to noise from a PC power supply making it through a firewire port, into my external M-Audio Firewire 410 box and then into my Behringer monitors. The give away was when Vegas was rendering the level of the sound would change.

Also take on board Grazie's suggesting of turning off or moving any device that uses RF. Once you know what the problem is you can better work on a fix, it may be as simple as one of those clip on ferrite cores on the right lead.

Grazie wrote on 1/1/2013, 2:00 AM
I'll try the ferrite core clamp thingie. Presently, and realising that the Cable was acting like a receiving aerial, I turned the wiring into a messy figure-o-eight configuration and that killed the influence of the WiFi signal or whatever is emanating from the Modem, could even be a badly grounded BT box itself?

Ferrite . . .

Cheers Bob,

TheHappyFriar wrote on 1/1/2013, 8:29 AM
Darn, Bob beat me to it: the instances of hum I've had almost always have come from two thigs:
1) the PC itself
2) using AC power vs battery on my camera.

The cases are metal, the insides are metal, the screws are metal, the connectors are metal, the power goes somewhere and I could hear it via the speakers.

I've heard it happen when rendering, when using the HD, when juts having the power on.

Since it was from inside the machine I double checked all the cables inside. Didn't help. turns out what did help using the mixer for everything & then just having an audio out from the mixer going to the PC, then the audio from the PC out going to the recording deck we were using, which was also hooked up to the mixer.
Woodenmike wrote on 1/1/2013, 11:46 AM
Lots of good info...going to take a while to check it all out. I plugged my line out into my other workstation and...still have hum, although not quite as loud. Will check out wireless modem (seems like the hum started bothering me more shortly after installing that, but didn't associate it with the modem at the time). Ultimately I am going to have to re-configure my plug-ins in my editing room...I have 8 separate circuits down there, and there may be some cross pollination of power.
musicvid10 wrote on 1/1/2013, 12:04 PM
"Buy this and put it in line between your sound card and mixer. It will solve the ground loop problem you mentioned and ones you don't know you have. "

Looks like a passive direct box / attenuator to me, but with all the fancy language, it's hard to tell.
I notice that this item has not yet been reviewed, and the price might be a reason why.

If it "is" ground loop hum (and other possibilities have not been ruled out), and depending on your connectors, then a direct box with a ground lift switch is probably all you need. But you can get them a lot cheaper than that, maybe save yourself $20-35 on a couple of matchboxes or dual DI.
Former user wrote on 1/1/2013, 2:29 PM
Maybe something useful here on Wiki?

Mains Hum