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HDMI monitors causing interference on mic channels

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HDMI monitors causing interference on mic channels

Postby Jaacobrs » Fri Jan 22, 2021 5:01 pm

Hope I'm posting to the most relevant forum, please re-direct me if there is another forum that best suits this issue.

Having a buzzing sound on all my mic channels, and I believe it's some sort of ground loop issue caused by the HDMI monitors. Let me describe my studio setup.

It's a podcast studio, square room with 2 sofas on opposite sides, above each sofa is an HDMI monitor, and 2 mic arms. The XLR cables run along the floor around the room into the control room, and the wires for the monitors run upwards to the ceiling, where they go into a power adapter. I also have 4 LED light panels at each 4 corners, these cables are also running along with the ceiling into the same power adapter as the monitors.

I've done some fault-finding, and un-plugged every plug in the room until I can locate the buzzing/interference and I've isolated the issue to the monitor power cables, however interestingly, when the monitors are plugged in, but the HDMI cables are unplugged, the interference is gone.

Steps already taken to try to fix the issue:
I've made sure all the power cables run-up to the ceiling, and all the XLR cables run on the floor so they're as far away from each other as possible.

My interface is running off a different power outlet from all the lights and monitors.

Any help would be really appreciated as I'm pulling my hair trying to get rid of this interference. I would opt to simply remove the monitors but they serve an important function in the podcast studio.

Thanks
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Re: HDMI monitors causing interference on mic channels

Postby pk.roberts » Fri Jan 22, 2021 5:36 pm

The bit of information that might help is, other than by the mains, how (if at all) are the video monitors and the audio system connected together? Is there a computer at the heart of this which is recording audio and video and feeding the video monitors? Is there an audio interface as well as the mixer?
With the use of 'double insulated' equipment, and any unbalanced audio cables it's almost certainly a ground loop somewhere exacerbated by the noise produced by inexpensive switch mode power supplies.
I have used variety of fairly inexpensive ground loop isolators on unbalanced audio in the past to 'break the loop, e.g.
https://cpc.farnell.com/w/c/audio-visua ... 20isloator
and as a last resort, when time was of the essence, have also had to resort to 'optical' HDMI leads which have also sorted the problem.
Usual safety note; never disconnect safety earth from the mains plug!
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Re: HDMI monitors causing interference on mic channels

Postby Jaacobrs » Fri Jan 22, 2021 6:27 pm

pk.roberts wrote:The bit of information that might help is, other than by the mains, how (if at all) are the video monitors and the audio system connected together? Is there a computer at the heart of this which is recording audio and video and feeding the video monitors? Is there an audio interface as well as the mixer?
With the use of 'double insulated' equipment, and any unbalanced audio cables it's almost certainly a ground loop somewhere exacerbated by the noise produced by inexpensive switch mode power supplies.
I have used variety of fairly inexpensive ground loop isolators on unbalanced audio in the past to 'break the loop, e.g.
https://cpc.farnell.com/w/c/audio-visua ... 20isloator
and as a last resort, when time was of the essence, have also had to resort to 'optical' HDMI leads which have also sorted the problem.
Usual safety note; never disconnect safety earth from the mains plug!

Hi pk.roberts, thank you for your response.

Yes my Macbook is at the heart of everything. Audio interface connected with USB-C, and then the two HDMI monitors, no mixer in the situation. Ive used in some cases a daisy chain of extension cables to run power from one side of the room to the other, so all my lights can be turned off/on with one plug etc.

All the XLR cables i have used are advertised as balanced, (i was under the impression all XLR cables are balanced to be honest). I have also tried many different XLR cables but the issue seems to exist whatever cable i use.

The mention of buying ground isolators interests me, however all of the products listed on the link are with phono or jack inputs, none of which are used in my setup, anything you would recommend? Optical HDMI leads are very expensive so i'm hesitant to try this just yet but perhaps in the future.
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Re: HDMI monitors causing interference on mic channels

Postby Mike Stranks » Fri Jan 22, 2021 6:31 pm

Yup! I agree with 'pk'...

Some here will know I've just started fiddling about with various HDMI interconnects, HDMI-USB connectors and (aborted) HDMI switchers...

All my audio links are balanced.

Noticed last night that there's a marked increase in the 'noises' off when all the kit is powered on. When the video side is down then all returns to its previous state...
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Re: HDMI monitors causing interference on mic channels

Postby MOF » Fri Jan 22, 2021 6:50 pm

My interface is running off a different power outlet from all the lights and monitors.

Try running the monitors on the same circuit as the interface.
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Re: HDMI monitors causing interference on mic channels

Postby James Perrett » Fri Jan 22, 2021 6:57 pm

Jaacobrs wrote:I've made sure all the power cables run-up to the ceiling, and all the XLR cables run on the floor so they're as far away from each other as possible.

My interface is running off a different power outlet from all the lights and monitors.

There should be no need to separate audio cables and power cables in that way and it could well be making things worse. You need short, direct paths to ground with as little difference as possible between the ground potential so ideally everything in your system should be plugged into the same power socket.
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Re: HDMI monitors causing interference on mic channels

Postby Sam Spoons » Fri Jan 22, 2021 8:05 pm

I think the OP has a separate control room so it might be difficult to run from a single socket?
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Re: HDMI monitors causing interference on mic channels

Postby Jaacobrs » Fri Jan 22, 2021 8:51 pm

James Perrett wrote:
Jaacobrs wrote:I've made sure all the power cables run-up to the ceiling, and all the XLR cables run on the floor so they're as far away from each other as possible.

My interface is running off a different power outlet from all the lights and monitors.

There should be no need to separate audio cables and power cables in that way and it could well be making things worse. You need short, direct paths to ground with as little difference as possible between the ground potential so ideally everything in your system should be plugged into the same power socket.

I’ve read on other related articles it’s best to separate power and audio cables and only cross them at right angles, hence why I tried to separate them as far as possible.

I shall try running everything off one socket in the morning, but the reason I haven’t done that already is because I assumed it would be dangerous to run 8-9+ Devices off one plug?

Can anybody offer some clarity on this? Thanks
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Re: HDMI monitors causing interference on mic channels

Postby CS70 » Fri Jan 22, 2021 9:33 pm

For studio stuff, shouldn't really be an issue. Not an electrician, but the circuit breaker will trip if you try to draw more current than it will handle - it's there and size correctly (hopefully) but nothing more than that. The only risk I know of is local overheating if thin wire is used where many devices requiring lots of power drawing from it. But we're talking stuff like electrical heaters of incandescent lamps requiring lots of wattage (and thus summing up to a large amperage). If the thin wire is in the wall, that can be dangerous as a fire may start unseen.

Also, in practical terms, if you use a single switch to turn everything on at the same time, you may generate a temporary power request spike in the circuit and trip the breaker. For example, if I ever have to disconnect the studio gear, I turn off the speakers before giving power again and turn them on again after the rest is on.

For your problem, it sounds like a ground loop and the HDMI cable happen to be in the perfect position to close it.
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Re: HDMI monitors causing interference on mic channels

Postby Sam Spoons » Fri Jan 22, 2021 10:43 pm

You definitely won't overload the socket powering a small studio rig, even including a couple or three LCD monitors, some monitor speakers and a few LED lights and cameras. Most of those devices will draw less than .5A* from the mains and a single plug can supply 13A. The sockets on a single circuit can supply, usually, 32A. If you have some large power amps or electric heaters on the circuit then you might need to do the sums but for normal studio gear probably not.

Post a list of the gear you are running off the circuit if you like and somebody will tell you if you need to get the calculator out.

* as an example your MacBook probably has a 60 watt power supply, that will use, at most, .26A
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Re: HDMI monitors causing interference on mic channels

Postby James Perrett » Fri Jan 22, 2021 10:52 pm

Jaacobrs wrote:I’ve read on other related articles it’s best to separate power and audio cables and only cross them at right angles, hence why I tried to separate them as far as possible.

I shall try running everything off one socket in the morning, but the reason I haven’t done that already is because I assumed it would be dangerous to run 8-9+ Devices off one plug?

There are all kinds of recipes that you can follow but the problem is that this is engineering - not cooking - so you need to have an understanding of why you are doing what you are doing.

Separating power and audio is a good idea if you are using unbalanced audio connections but not so vital with balanced connections although it is usually good practice to keep them a few cm apart. The screening in your audio cables is there to prevent interference and balanced connections will reduce interference even further.

As far as running lots of things from a single socket is concerned - you need to look at the power consumption of all the items. If you are in the UK a wall socket can supply up to 3000W. A single electric heater could well take that amount of power on its own but computer monitors are often under 100W so you could use 30 of them or more from a single socket. Other studio gear takes even less power so most people will be able to run all their studio gear from a single socket. If you have a big 2" tape machine and matching mixing desk then you may need more power but not much more than a standard socket can supply.
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Re: HDMI monitors causing interference on mic channels

Postby pk.roberts » Sat Jan 23, 2021 12:58 pm

Having thought about the setup you describe, I'm wondering if there is a mains earth anywhere in the system? It's quite possible that everything is either double insulated or powered by an external power supply that doesn't pass an earth through to the equipment. This could mean that there is nowhere for the 'digital shash' to go (apologies to all the engineering types here for the simplified explanation ;) ) So rather than the problem being caused by an 'earth loop', it could actually be a 'lack of earth' issue.
I know that there have been previous discussions here about supplying an an earth via a commercial plug type device designed to do that (which I'm sure has also been reviewed in SOS), but my 'google foo' has let me down - can anyone else find the link?

E2A - I just found it!
https://www.soundonsound.com/reviews/gr ... ction-plug
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