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[Wesley Key]

Good evening,

It has come to my attention that the videos that our church posts to youtube have a loud hum.  This hum is present no matter which microphone we use.  No hum is heard over the church speakers, but only on the videos.  Any help would be appreciated.  Here is a sample video with the issue --- https://youtu.be/WjJDrTw_u-0

[Scott Holtzman]

Good evening,

It has come to my attention that the videos that our church posts to youtube have a loud hum.  This hum is present no matter which microphone we use.  No hum is heard over the church speakers, but only on the videos.  Any help would be appreciated.  Here is a sample video with the issue --- https://youtu.be/WjJDrTw_u-0

You have a ground loop issue.  You need to provide details on the system.  Since it is not in whatever output feeds the PA from the mixer that means it is downstream of the output that feeds the live threads.


If you are not using a dedicated caster with balanced inputs you should at least have a decent interface on the computer that is feeding the broadcast.  I highly recommend using a program like Open Broadcaster (it's free) for any live broadcasts you do. 

[Steve-White]

A simple block diagram of the system would be very helpful.

[Brian Jojade]

Most definitely sounds like a ground loop.

The solution to this problem likely will be as simple as an isolation transformer between the mixer and the computer. These can be called many different things.  Prices range from about 10 bucks for a cheap one, to a couple hundred for active ones.  Start with the cheap one, since it's a low investment.  You can probably find them locally at any audio shop. They are commonly used in automotive installs as well.

If you're using a laptop, you can also try running off battery. In many cases, this eliminates the ground loop as well.  You may be tempted to lop the ground pin off of the power supply too.  Not recommended, but could eliminate the noise.

[Steve-White]

#1 most probable cause is a ground loop.  Beyond that, the next thing to look into is the power supply for the computer.

[Mike Caldwell]

If it's an analog connection from the mixer to the device that use for streaming you need an isolation transformer in the line.
They also need to place the lapel mic higher.

[Wesley Key]

A simple block diagram of the system would be very helpful.

Wireless mic transmits back to my AV room.  Connected via XLR to a mixer.  Audio outputs from the mixer feed a simple camcorder.  Camcorder records to an SD card.

[Scott Holtzman]

Wireless mic transmits back to my AV room.  Connected via XLR to a mixer.  Audio outputs from the mixer feed a simple camcorder.  Camcorder records to an SD card.

Ok, unplug the mic is the hum still there?  You need to check each block one at a time?  If no hum at RX then jack into the mixer without the mic connected.  If you have hum keep going. 


How is the PA connected?  Is it on main out and the camcorder on a bus?  Details are important.  What kind of mixer?

[Wesley Key]

Hum is present on all four microphones after testing.  I did some isolating.  Zip tied certain wires so they don't touch other wires, etc.  No idea how it happened, but hum is now gone.  Thanks for all the help.

[Mike Caldwell]

Hum is present on all four microphones after testing.  I did some isolating.  Zip tied certain wires so they don't touch other wires, etc.  No idea how it happened, but hum is now gone.  Thanks for all the help.

"Fixes" like that kind of scare me in not knowing what the actual problem cause was.

 What were the certain wires that you moved? Was it actual interaction between the wires or did moving them move something else like a connector that is now making a better connection?

[Dave Pluke]

"Fixes" like that kind of scare me in not knowing what the actual problem cause was.

Agreed.

I'd undo the bundle and shake the daylights out of everything to try to locate the culprit - 'cuz it's gonna come back and likely at the worst possible moment (according to Murphy).

Dave

[Scott Holtzman]

Hum is present on all four microphones after testing.  I did some isolating.  Zip tied certain wires so they don't touch other wires, etc.  No idea how it happened, but hum is now gone.  Thanks for all the help.

That's hardly a fix.  Those kind of intermittent issues is what bites you in the tush.  Don't you have curiosity what the issue is?  Are you satisfied with the resolution?  How do you think the elders at the church would feel?  This could come back at worst moment.


The whole deal of recording to the camera is also a Rube Goldberg mess.  Need to learn how to use a video software package.  Money is not an issue as many are free. 

[Steve-White]

Hum is present on all four microphones after testing.  I did some isolating.  Zip tied certain wires so they don't touch other wires, etc.  No idea how it happened, but hum is now gone.  Thanks for all the help.

As my colleagues have advised you, the problem isn't resolved - you essentially put a bandaid on cancer.

There's a dirty connector, shield shorted, cold solder joint, broken conductor or similar issue there waiting to manifest itself at the least opportune time.

Consider investing in a cable tester like one of these:  https://dbxpro.com/en-US/products/ct-2

If some simple bundling and wire ties eliminated the noise, it should be fairly easy to isolate it.

[John Roberts {JR}]

Last week I watched an old black and white movie from the 30s-40s and there was hum on the soundtrack. It wasn't a lot and was most audible when compression in the broadcast chain cranked up the gain during a quiet part.

Hum Happens... I suspect some movies add it for effect, like the huge guitar amp in back to the future...

JR 

[Brian Jojade]

Hum Happens... I suspect some movies add it for effect, like the huge guitar amp in back to the future...

JR

Like the obligatory feedback that happens whenever someone walks to a mic. That's movies. You don't want it in real life.

[Wal Mann]

Hum Happens... I suspect some movies add it for effect, like the huge guitar amp in back to the future...

JR

Also some Sci-fi movies and TV shows have a continuous hum/rumble when on spacecraft of all kinds, I thought it was used to mask other noise intrusions that didn’t belong.

Wal

[Scott Holtzman]

Also some Sci-fi movies and TV shows have a continuous hum/rumble when on spacecraft of all kinds, I thought it was used to mask other noise intrusions that didn’t belong.

Wal

Yes, Star Trek TNG had that and it was a pain.  I guess folding space with a warp drive also rumbles like a piston engine!

[Jaspreet Singh]

Hum is present on all four microphones after testing.  I did some isolating.  Zip tied certain wires so they don't touch other wires, etc.  No idea how it happened, but hum is now gone.  Thanks for all the help.

Glad it is fixed. I am a new learner too but I learned if you have low voltage and high voltage wires running parallel for 2 ft within 2 ft it will cause disturbance. Second reason for hum like that is a loose connection. 2 main issues

[Brian Jojade]

Glad it is fixed. I am a new learner too but I learned if you have low voltage and high voltage wires running parallel for 2 ft within 2 ft it will cause disturbance. Second reason for hum like that is a loose connection. 2 main issues

Hum is typically introduced either as a ground loop from devices on 2 different ground points, or through external noise inducted into the signal line.

Those arbitrary distance numbers are based on pretty much nothing.

With a proper balanced signal, running parallel lines long distance can be done without issue.  Unbalanced cables are more susceptible to interference, but with good shielding and grounding you can be fairly noise free.

Poor connections on balanced connections can mean losing one side of the balanced signal. This results in a loss of volume that can be adjusted for and seemingly be a non issue, but at that point, you're now subject to noise interference.

Ground loop issues with bad ground connections means devices may be at different ground potentials and hum may seemingly come and go.  Creating a solid ground is a solution, as well as transformer isolation of the devices so that it doesn't matter that they are at different ground potentials.  Transformer isolation is generally the most reliable solution.

[Patrick Tracy]

Glad it is fixed. I am a new learner too but I learned if you have low voltage and high voltage wires running parallel for 2 ft within 2 ft it will cause disturbance. Second reason for hum like that is a loose connection. 2 main issues

I routinely ran a 100' extension alongside a 100' snake (typically about 80' of close proximity) with no audible hum. It actually solved hum problems due to unbalanced returns and using a nearby outlet to power FOH.

[Jaspreet Singh]

Hum is typically introduced either as a ground loop from devices on 2 different ground points, or through external noise inducted into the signal line.

Those arbitrary distance numbers are based on pretty much nothing.

With a proper balanced signal, running parallel lines long distance can be done without issue.  Unbalanced cables are more susceptible to interference, but with good shielding and grounding you can be fairly noise free.

Poor connections on balanced connections can mean losing one side of the balanced signal. This results in a loss of volume that can be adjusted for and seemingly be a non issue, but at that point, you're now subject to noise interference.

Ground loop issues with bad ground connections means devices may be at different ground potentials and hum may seemingly come and go.  Creating a solid ground is a solution, as well as transformer isolation of the devices so that it doesn't matter that they are at different ground potentials.  Transformer isolation is generally the most reliable solution.

Great info thanks!
My question now is, would running regular speaker wire (just a red and black) be more vulnerable than a balanced XLR cable or would a speaker wire be safe too as long as it is wired properly?

[Scott Holtzman]

Great info thanks!
My question now is, would running regular speaker wire (just a red and black) be more vulnerable than a balanced XLR cable or would a speaker wire be safe too as long as it is wired properly?

It's more complex than that.  We run shielded single ended and balanced connections which can benefit from shielding but can get away without it though in practice we always use shielded cable in entertainment application on signals that are low in voltage like a microphone.  These signals are more susceptible to interference because it is easy for the induced interference to be at a greater level than the actual signal. 


A speaker on the other hand takes quite a bit of power to produce an audible signal.  Inducing that much power would be very difficult. 


Does this make sense?

[Jaspreet Singh]

Does this make sense?

Yes, thank you

[ProSoundWeb Community]