How do i get rid of electrical hum in my recording set-up?

Sikes

New member
So i put together a little home recording set up with the following gear:

15' Macbook pro (2016)
M-audio profire 2626 audio interface
Yamaha HS8 studio monitors

Everything is working as it should but i just can't seem to get rid of this electrical hum thats on my speakers at all times. First i tried simply using balanced cables for the connection from my interface to the speakers and it didn't do anything, then i bought a ground loop isolator (ART DTI) and that lowered the intensity of the hum quite a bit but it's still there, very quiet but still noticeable.

The ART DTI ground loop isolater has this pin for connecting a ground wire to it but i am wondering how that works exactly? Do you just take any old metal wire, and then what do you connect it to?

To be clear the ground loop isolater is located in between the output of the interface and the input of the monitors. I also need to point out that when connecting the power adapter of the macbook the hum gets a lot more quit but even with the adapter plugged in the hum is still there.

So if any of you have any knowledge of electricity and sound and can help me out with this i would greatly appreciate it!

(attached image shows the ART DTI ground loop isolator, on the far left of the device is a piece of metal which i believe is used for attaching a grounding cable)IS505495-01-02-BIG.jpg
 
Last edited:
When you run the laptop on battery is there still a hum? Does the hum get louder when you turn up the volume on the monitors? The hum is not recorded, correct?
 
Are you saying the hum is louder when the MacBook is running on battery and quieter when it is running on AC? That is odd.

How about when the computer is disconnected from the interface? (Always connect/disconnect the Firewire device with the MacBook powered down!)

If the hum reduces when the MacBook is plugged in, I'm suspecting a problem with that interface (or possibly its power supply?), honestly, which is why I'd like to get the computer out of the picture. Did you buy it used? Is it the correct power supply for it? Any way for you to test another interface?
 
I'm sure you'll get more specific suggestions, but here's one along the lines of the path you've already set upon :

(This is not a ground lift)

Ebtech Hum X Ground Loop Hum Exterminator | Sweetwater
The speakers are the only ones with a 3-prong plug, if I understand this setup. Seems like they'd hum just all by themselves if they were at fault, and probably not both.

I'd invest in one of those cheap AC outlet testers too.

(I've used a FireWire interface with a MacBook and powered monitors for years and never had any hum issues. Different interface manufacturer, but still...)
 
Have you checked that your balanced cables are wired correctly? This sounds like a ground issue but properly balanced connections shouldn't have these issues which is why I'm suspicious of the cables.
 
Is the power point properly earthed, or has it got a bad resistive earth?

Have you tried lifting (unsoldering) the shield on the balanced cables to the monitors, lift at the monitor end of the cable.

Alan.
 
Thanks for all the reply's guys! Finally i found a forum where people actually reply to question, i love this place already :)

To clarify: The hum gets a lot more quiet when the power adapter is plugged in compared to when it's running on the battery.

Also, the hum does indeed get louder as i turn up the volume of the speakers so all of the issues are indeed pointing to the audio interface. I have also tried a different interface (focusrite saffire 6), this interface gives less hum on it's own but as soon as i plug in for instance a synth or an instrument thats connected to a power outlet the hum gets really bad. So maybe there is just an issue with the electrical circuit where i live? I live in Europe (Belgium), and all sockets have three pins here so i didn't think that would be the issue.

I will check the balanced cables to see if the ground wire is connected if so i will disconnect it on one side (that should help right?)

In the meantime i will also start reading some of the pdf's posted here, i need to brush up on my knowledge of electricity anyway.

Edit: Disconnecting the lift pin (at the end of the connector which connects to the monitor) on the balanced cables didn't work
 
Last edited:
'Ow do Sikes. First of all I DO NOT LIKE those Ebtech hum "eliminators"! They fook about with the earth path and that might be acceptable in 110V land (but I wouldn't) but not with "proper" 230V nominal. The "Earth" safety system was designed by people who KNEW WTF they were at, never mess with it.

Rant over. The Hum: Can be a trial tracking this down. Your first attempts do indicate a hum (aka ground/earth) loop but you might have a residual hum from a completely different source.

First stop, the monitors. Diss all audio cables and fire them up, set volume pots to min' and with ear close to speaker is there a hum? There will be a bit of hiss but I would expect NO hum. Now advance the VCs and IMO there still should be no hum but there might be a tiny bit at the top end of the pot. N.B. It is very possible for active speakers to produce a mechanical hum, i.e. not from the cone, from the power transformer.

If the speakers seem blameless rig the system with the Art isolator box in line. Play out a track at a decent level* and then stop it and check the hum. If audible at the mixing position you have a problem. Now unplug the computer from the AI (FireWire?). Still hum? That would actually be good news because it eliminates a FWire hum loop. Rare but vitually incurable if it happens.

You could post a "silent" recording? Turn all the pots to zero on the interface then make a 30 second recording of "nothing" (44.1kHz and 24 bits) For me it is best attached as a 320k MP3 clip. I can then look at it and possibly help with other suggestions.

Dave.
 
Thanks for all the reply's guys! Finally i found a forum where people actually reply to question, i love this place already :)

To clarify: The hum gets a lot more quiet when the power adapter is plugged in compared to when it's running on the battery.

Also, the hum does indeed get louder as i turn up the volume of the speakers so all of the issues are indeed pointing to the audio interface. I have also tried a different interface (focusrite saffire 6), this interface gives less hum on it's own but as soon as i plug in for instance a synth or an instrument thats connected to a power outlet the hum gets really bad. So maybe there is just an issue with the electrical circuit where i live? I live in Europe (Belgium), and all sockets have three pins here so i didn't think that would be the issue.

I will check the balanced cables to see if the ground wire is connected if so i will disconnect it on one side (that should help right?)

In the meantime i will also start reading some of the pdf's posted here, i need to brush up on my knowledge of electricity anyway.

Edit: Disconnecting the lift pin (at the end of the connector which connects to the monitor) on the balanced cables didn't work

Make sure all gear is plugged into the same socket/branch circuit(use a power bar if necessary).
Also don't plug wall warts side by side on any socket/power bar(give some space between).
Last,double check cabling and separate power and audio cables.

Gary
 
Just looked up that Art DTI. Not exactly what I would have chosen, the Cleanbox 2 is more suited perhaps to simple earth isolation but the DTI should (and does) make some improvement.

Further thoughts. Make sure the Art box is at the AI end and the long run goes from that to the monitors. As with all these traff boxes they are OUTPUT isolators not 10k INPUT bridging transformers.
Note too that the transformers themselves can pickup hum! Any residual might "tuned out" by slowly twisling the box about, even end over end.

Wall rat/line lump power supplies are notorious for spewing out hum fields! Keep them at least 500mm from audio kit and cables.

Dave.
 
Can I ask a question? Is the hum we are talking about 50 or 60Hz AC mains hum, or are we talking about something other than this? We have had questions where on hearing it, discovered the 'hum' isn't hum at all, but something with data and loads of harmonics, and the cure for that is quite different. We're assuming we are all talking about the same hum, but I'm left wondering if we're not!
 
Can I ask a question? Is the hum we are talking about 50 or 60Hz AC mains hum, or are we talking about something other than this? We have had questions where on hearing it, discovered the 'hum' isn't hum at all, but something with data and loads of harmonics, and the cure for that is quite different. We're assuming we are all talking about the same hum, but I'm left wondering if we're not!

Here is a short 20 second recording i made of the hum: vocaroo (.) com/i/s0wXNblTWjFI

I put the monitors on max volume so the hum would be clearly audible in the recording.
 
Not simply basic 'hum', but some other crap in there as well. Downloaded sikes wav file, loaded up in Audacity and normalized to bring it up to listening level. New mp3 file as an attachment.

What else do you have on the desk/table where the gear is located? Florescent lighting/CFL bulbs, device with a transformer nearby to cables or the gear or anything else that could possibly create electrical noise?
 

Attachments

  • noise.jpg
    noise.jpg
    121.7 KB · Views: 12
  • sikes wav.mp3
    324.9 KB · Views: 11
Yeah, that's ugly. Something seriously futzing with the AC. Lights, dimmers, who knows. And honestly still haven't ruled out the interface, though OP said he tried a different one (different power supply I'd assume, or was it on bus power?).

log scale shows something generating a nice set of harmonics!

Screen Shot 2018-11-27 at 5.03.13 PM.png
 
Yes, that is horrible. Rightmark give another view. The strong 3rd harmonic suggests to me a mains transformer being run very close to its VA limit. Could indeed be a choke in a lamp.

The level at 50Hz shows it is induced hum and not the 100Hz you get from poorly filtered power supplies.

Dave.
 

Attachments

  • Spectrum sikes.png
    Spectrum sikes.png
    13.3 KB · Views: 7
Back
Top