Mic Interference with LED lights

[thomatkinson]

Hi everyone,

Has anyone ever had a problem with audio interference caused by LED video lighting?

I’m using a Sennheiser MKE600 microphone (battery powered) with a Canon R5. It sounds great, until I turn on my Nanlite Forza 500 (mains powered). A sort of electrical static interference noise turns up on the recorded audio and can be heard over monitoring headphones during recording. It gets worse if the power on the light is turned up. And it stops when I turn off the light. It doesn’t happen with the R5s onboard mic or with a Rode Stereo Mic Pro.

I’ve tried the following with no success:

- turning off fan on Forza 500

- Moving Forza head and ballast away / into a different room / behind a closed door

- with and without XLR lead

- with and without high pass filter on mic

- with and without mains extension cable / different circuits in different rooms

- with and without headphones or video monitor plugged in

- reducing mic levels to about 25%/30% on the R5 obviously reduces the noise, but doesn’t eliminate it.

Any ideas? Maybe I need different / better shielded cables (though I think they’re fairly decent ones)? Do I need a different mic? Would battery, rather than mains power for the Forza 500 help?



I’d be very grateful for any suggestions / experiences!

Thank you,

Thom

 

[Tom Stites]

Thom,

I don't have experience with either of your products, but much experience tracking down audio and video gremlins.

Your troubleshooting methodology looks pretty thorough, though I have one question. When you mention, "with and without XLR lead" what exactly do you mean? If you have the XLR to 3.5mm lead plugged into the camera, but not the mic, do you get the interference? Or only when the mic is also connected and switched on? What if the mic power is switched off?

As you may know, LED lighting systems typically PWM the LED's at frequencies that can be problematic to vary brightness, color balance, etc. Also switching power supplies are used in most of the devices and these can generate considerable interference, as well. Obviously, the light in generating the RF interference that varies with your brightness adjustment.

I'd contact both Sennheiser and the lighting manufacturer to get their take on this. Pending the answer my questions above, not much else you can do but try another copy of the same mic and/or lighting unit. It's quite odd that the interference remains when in another room and at a considerable (?) distance. Do you get any interference from it that affects any other audio equipment in the area, say an audio monitoring system that's part of your edit system?

Cheers and good luck!

 

[thomatkinson]

Hi Tom,

Thanks for your reply - much appreciated.

To answer your questions:

When I say "with and without XLR lead" I mean that the problem occurs when the mic is boomed a few meters away, and connected to a 5m XLR cable which is in turn connected to a short XLR to 3.5mm adaptor, which goes into the camera's MIC socket. And it also occurs without the XLR lead, when the mic is connected to just the XLR to 3.5mm adaptor and positioned on top of the camera. I have only one XLR cable but I've tied two identical XLR to 3.5mm adaptors, neither of which fixed the issue.

There is no interference if the mic is not plugged into the cables, or if the mic is plugged into the cables and switched off. There is also no interference using the other microphones mentioned, though these do use different cables or no cables, so I guess I can't entirely discount the cables as an issue.

When I put the light in another room and close the door, the interference is possibly less. But it's ultimately only a few metres away. I do notice the proximity of the mic to the lamp head seems to change the interference subtly, though not enormously.

I'm trying to contact Sennhieser and Nanlite but no response yet. Unfortunately my internet connection is down at the moment, which is making things a lot more tricky for online chats and so on!

A couple of working theories that I wonder if you might have a view on:

1. Are there better, more heavily shielded cables I could try?

2. Could this be an issue with the wiring in my house? If this is a realistic possibility I could try to impose on someone to let me test elsewhere.

3. Would the issue be solved if I bought batteries for the Forza 500 and took it off the mains power?

4. Is there anything I can do to shield anything myself - tin foil etc?

Thanks again. I've had no progress elsewhere so far, so any thoughts are very welcome. I have about 48 hours left to figure something out before a job!
Thanks,
Thom

 

[Tom Stites]

Hi Thom,

Thanks for the clarification...

I'd discount this being a cable problem...seems to be an electronics problem with the mic itself not being properly shielded against RF interference...or at least the frequency band that the light is emitting. Could be a design issue with the mic or something in the electronics module or wiring that is out of spec...ferrite beads or shielding improperly installed.

If it's easy and not too costly to battery power the light, that's worth trying...that would take your mains wiring, both internally and externally, out of the equation. I wouldn't expect the problem to be your mains wiring other than to the extent that the lamp is coupling it's RF interference output to your house wiring and making it a large antenna distribution system much like a powerline WiFi extender. Sometimes switching power supplies can send RF back down the mains if the incoming power is not properly shielded and filtered in the unit.

Likely this problem is an unlucky confluence of a sensitive, possibly defective mic and a poorly designed or faulty light that is emitting excessive RF. Running out of options to figure this out without swapping out one or both of the units and seeing what you get...but you have a clock ticking.

If you have an AM radio, portable preferred, you may want to check and see if that light causes major interference in the radio...you can tune up and down the dial and see if you get any strong interference that follows the light being on/off or changing power levels. If so, see how far away it causes problems...if still very strong more than 10-20m away, I'd say that's excessive, but it's all relative. I've got an LED strip lamp over my sink in my kitchen that reeks havoc on an AM radio on the counter...makes it unusable if the light is on.

 

[Andrew S10]

You could try making a cable with Neutrik EMC connectors , and see if that eliminates the RF issues.

 

[John Vickers]

Not guaranteed, but can fix or reduce some cases of interference:

Do you have some clip-on ferrites lying around?

Like this: https://www.amazon.co.uk/Dreamtop-Clip-Ferrite-Suppressor-Diameter/dp/B01MG8GQ1F/

?

If not, get 2 packets of something like that.

Where to put them?

On the cables you think are causing a problem, a few inches from the end of the cable near the gadget you think is the source of the interference, or that you think is being interfered with.

Illustrations of how to put them on: https://support.klipsch.com/hc/en-us/articles/4416949281044-Using-Ferrite-Chokes-

In this case I'd try putting them:

• On the power cable from control box to light head, near the light.
• On the power cable from control box to light head, near the control box.
• On the mains cable into the control box, near the control box.
• On the XLR to 3.5mm adaptor cable, near the 3.5mm plug.

Other ideas:

• If you have a portable recorder: connect microphone to recorder with XLR cable, record sound with on camera mics, and sync in post.
• Is the camera (I guess Canon R5) running off USB or battery? If USB, try battery, or put ferrite on USB cable.
• Are there any other long cables attached to the camera? Particularly cables to other mains powered devices? HDMI monitor? Put ferrites on those cables too.

This is all a bit scattergun, but it's not always obvious where the problem is.

Couple more comments inline below:

Hi Tom,

Thanks for your reply - much appreciated.
To answer your questions:

When I say "with and without XLR lead" I mean that the problem occurs when the mic is boomed a few meters away, and connected to a 5m XLR cable which is in turn connected to a short XLR to 3.5mm adaptor, which goes into the camera's MIC socket. And it also occurs without the XLR lead, when the mic is connected to just the XLR to 3.5mm adaptor and positioned on top of the camera. I have only one XLR cable but I've tied two identical XLR to 3.5mm adaptors, neither of which fixed the issue.
There is no interference if the mic is not plugged into the cables, or if the mic is plugged into the cables and switched off. There is also no interference using the other microphones mentioned, though these do use different cables or no cables, so I guess I can't entirely discount the cables as an issue.
When I put the light in another room and close the door, the interference is possibly less. But it's ultimately only a few metres away. I do notice the proximity of the mic to the lamp head seems to change the interference subtly, though not enormously.

I'm trying to contact Sennhieser and Nanlite but no response yet. Unfortunately my internet connection is down at the moment, which is making things a lot more tricky for online chats and so on!
A couple of working theories that I wonder if you might have a view on:
1. Are there better, more heavily shielded cables I could try?

Shielding doesn't always help.

2. Could this be an issue with the wiring in my house? If this is a realistic possibility I could try to impose on someone to let me test elsewhere.

Could be a factor, but not the cause.

3. Would the issue be solved if I bought batteries for the Forza 500 and took it off the mains power?

Possibly.

4. Is there anything I can do to shield anything myself - tin foil etc?

You don't need shielding.

I don't think that's completely silly. You could try wrapping the microphone in cooking foil, and see if the problem goes away. If it does, one problem is the microphone's sensitivity to RF interference, and you could see if less aluminium foil works. A lot of plastic cased gadgets have alimuminium foil stuck to the inside for shielding.

Technical stuff about ferrites: http://www.elmac.co.uk/Using_cable_ferrites.pdf

Ideally you want ferrites that come with a datasheet from an established electronic component manufacturer. But random ferrites off Amazon seem to work for me.

 

[thomatkinson]

Thanks Tom, Andrew, John - I appreciate the replies, which are all very interesting.

I've also spoken with an equipment supplier who thought it was likely to be a 'grounding issue' relating to the mains powered ballast for the light.

I've tried a few tests based on some of the suggestions/questions here and I have got a little more information:

- Proximity of the mic to the lamp head DOES clearly increase the interference
- Moving the mains cable around increases the interference
- Touching the light stand or the lamp head with my hand reduces the interference
- The interference happens on any circuit in my house
- The interference IS there with my Rode Stereo Mic Pro after all, it's just a littler harder to hear, which suggests it's less likely to be the mic at fault
- I'm afraid I don't have an external recorder or a radio to test some of your suggestions...
- The camera is not connected to the mains in any way. The interference happens with and without an external battery powered monitor
- Foil didn't seem to work, but it caused so many new problems with noise from the foil and generally looking ridiculous, that I decided to park that idea for now!

I've ordered some batteries for the light which will arrive tomorrow. The technical support people were fairly convinced this would work, so fingers crossed. I'll report back.

Thanks for the idea about the EMC connectors. This seems ideal, but I'll have to look into it longer term - I don't think I have the skill / know how to do this myself in time...

Adn thanks for the suggestion of the Ferrites - how clever! I'll order some to try.

Thank you again everyone - very kind of you!
Thom

 

[John Vickers]

Hi Thom,

Thanks for the clarification...

I'd discount this being a cable problem...

I would not. Cables can behave as antenna at radio frequencies.

Suppose the problem noise source is the light control box / power supply. It's unlikely to be a good antenna itself, but the cables connecting it to the mains supply, and to the light head can be good antennae.

seems to be an electronics problem with the mic itself not being properly shielded against RF interference...

Yes.

or at least the frequency band that the light is emitting. Could be a design issue with the mic or something in the electronics module or wiring that is out of spec...ferrite beads or shielding improperly installed.

If it's easy and not too costly to battery power the light, that's worth trying...that would take your mains wiring, both internally and externally, out of the equation. I wouldn't expect the problem to be your mains wiring other than to the extent that the lamp is coupling it's RF interference output to your house wiring and making it a large antenna distribution system much like a powerline WiFi extender. Sometimes switching power supplies can send RF back down the mains if the incoming power is not properly shielded and filtered in the unit.

Likely this problem is an unlucky confluence of a sensitive, possibly defective mic and a poorly designed or faulty light that is emitting excessive RF. Running out of options to figure this out without swapping out one or both of the units and seeing what you get...but you have a clock ticking.

If you have an AM radio, portable preferred, you may want to check and see if that light causes major interference in the radio...you can tune up and down the dial and see if you get any strong interference that follows the light being on/off or changing power levels. If so, see how far away it causes problems...if still very strong more than 10-20m away, I'd say that's excessive, but it's all relative. I've got an LED strip lamp over my sink in my kitchen that reeks havoc on an AM radio on the counter...makes it unusable if the light is on.

That's reasonable, but the AM radio might not be as sensitive as the microphone to interference at 10MHz or 100MHz (say) - where the problem might be. There are a lot of variables.

 

[John Vickers]

Thanks Tom, Andrew, John - I appreciate the replies, which are all very interesting.
I've also spoken with an equipment supplier who thought it was likely to be a 'grounding issue' relating to the mains powered ballast for the light.

Grounding issue? No. From what you say your camera and the microphone aren't connected to mains earth, and you don't have ground loops around your equipment. Modern power supplies isolate the output from mains earth.

I've tried a few tests based on some of the suggestions/questions here and I have got a little more information:
- Proximity of the mic to the lamp head DOES clearly increase the interference

- Moving the mains cable around increases the interference

The Light power unit mains cable? That means it's an antenna.

- Touching the light stand or the lamp head with my hand reduces the interference

You've re-discovered an old-skool electronics debugging technique.

"Put your finger on that transistor"

"It works now!"

"How many fingers have you got? We're going to have to ship one of your fingers with every product"

You've effectively connected a capacitor (you) to the lamp head, somewhat shorting out high-frequency electrical oscillations of the lamp head.

- The interference happens on any circuit in my house

Yup.

- The interference IS there with my Rode Stereo Mic Pro after all, it's just a littler harder to hear, which suggests it's less likely to be the mic at fault

I found that Rode Video Mic Pro also picks up Radio Frequency ("RF") interference. I found this out when using it at the same time as a Rode Wireless Go II transmitter was near it. Rode Video Mic Pro+ claims improved immunity to RF interference.

- I'm afraid I don't have an external recorder or a radio to test some of your suggestions...

A balanced XLR connection from mic to recorder, with balanced drivers and reveivers would have good immunity to interference. Then it doesn't protect the mic itself.

- The camera is not connected to the mains in any way. The interference happens with and without an external battery powered monitor

- Foil didn't seem to work, but it caused so many new problems with noise from the foil and generally looking ridiculous, that I decided to park that idea for now!

"Foil didn't seem to work, but"

Are you saying it stopped the interference, or not? I was confused by the "But".

I've ordered some batteries for the light which will arrive tomorrow. The technical support people were fairly convinced this would work, so fingers crossed. I'll report back.

If the light vendor is recommending a battery pack, they're saying they think the problem is with the power unit and the cables connected to it. Then they could be guessing.

If the battery pack is returnable, definitely get the ferrites anyway - if ferrites at both ends of both cables connected to the power unit fix the problem, they're a lot cheaper.

Thanks for the idea about the EMC connectors. This seems ideal, but I'll have to look into it longer term - I don't think I have the skill / know how to do this myself in time...
Adn thanks for the suggestion of the Ferrites - how clever! I'll order some to try.

 

[thomatkinson]

Thanks again!

Aplologies - for “but” read “and” - the foil had no obvious effect as far as I could tell

I’ll try the batteries, which I need anyway regardless of the noise issue. But it would be nice if they solved it too. The support tech said it was a bit of a trial and error situation and batteries were his best option to try first.

And I order the ferrites - will try those out tomorrow also - great idea.



Thanks and catch up when I’ve tested again
Thom

 

[thomatkinson]

Hi again everyone,

I wanted to update the thread in case it helps anybody out in future.

I received batteries for my light today and tested them out - it didn't work and the interference remains the same.

I've had a chance to test a different XLR cable - also didn't work.

And the Ferrites arrived too - I tested them on the cable between the battery pack and the lamp head (at one end first, then a second on the other end) and on the XLR to 3.5mm cable attaching the mic to the camera - neither worked.

Getting back to the basic facts, the only set up I've found which doesn't suffer from interference is when I use the built in mic on the camera. This suggests the problem is related to the XLR to 3.5mm cable or use of the input on the camera. I've tried two cables - good quality and more or less new - and there was no difference. And I've tried a different mic with a built in 3.5mm cable, which also picks up the interference.

Today (this is getting expensive!) I ordered a stand alone field recorder (Zoom F3) so I can plug the mic directly into it with the XLR and avoid the camera and 3.5mm connection entirely. It should arrive tomorrow. Hopefully it will solve the problem on it's own, or if not, it should give me much better sound quality and make it easier to remove the interference in post.

Unless there are any other ideas out there, I think I'll have to muddle through the shoot this way and figure out a long term solution afterwards. I'd like to have the option of recording sound direct to camera because many projects will require that convenience and speed, so the recorder wouldn't entirely be a solution.

Thanks!
Thom

 

[Andrew S10]

You can try running an aux cable from your F3's line-out port to your camera's mic input, but you might need a cable with an in-line attenuator to bring down the line-level signal down to mic level. This setup will function as an XLR balanced mic adaptor .

The F3 can record in 32-bit float, which is overkill most of the time, but can save your bacon when things go wrong.

 

[thomatkinson]

My Zoom F3 recorder arrived today and I just tested it out... it works! No interference! So, I think this narrows the problem down to using the 3.5mm mic connection on the R5.

Thanks, Andrew, for those points about the F3 recorder. It does sound fool proof which I'm quite happy about!

Great to have a solution in place for my shoot and just a bit of learning to do over the weekend to get it all ready. You're right that the F3 is overkill and it's going to be a little annoying and impractical for this particular shoot for a few reasons, but I'll take that over the interference.

I'd still like to get to the bottom of this and get things working correctly with a mic attached direct to camera. I'll contact Canon about it and see if they think it's a repairable fault (I'm starting to wonder if it is because no-one else seems to be having this problem), or just a quirk of the R5 in combination with the Forza 500. Also still waiting for advice from Nanlite about the light in case they have anything to offer.

Thanks for the tip about the line out port - I'll try this out at some point soon. The F3 manual actually tells you to do this with a regular aux cable, rather than the attenuated cable you suggested, but I'm out of my depth here - I'll have to find out some more about the best options and of course test whether it causes the interference to come back.

Thanks again everyone. I'll report back if I find an eventual solution for using the 3.5mm port.

 

[Andrew S10]

I did some Googling, and found this article on using an R5 with a Zoom F6 , which might be applicable to your situation.

Some mirrorless cameras can accept line-level signal, due to a built-in attenuator that can be activated in the menu. If your camera doesn't have a built-in attenuator, you'll need an aux cable with an in-line attenuator, unless your F3 can be set to output mic-level instead of line-level.

 

[thomatkinson]

Thanks Andrew. The R5 does indeed have a built in attenuator setting. It will be interesting to test this out and see if it works!

 

[John Vickers]

Thanks Andrew. The R5 does indeed have a built in attenuator setting. It will be interesting to test this out and see if it works!

If I understand right, what the R5 calls an "Attenuator" is really a limiter - it compresses loud sounds to avoid clipping.

But the F3 does have programmable gain/attenuation (+24/-48dB) on the line output, which should be plenty to make it work with the R5.

 

[thomatkinson]

Ah, ok, thanks for that!

 

[low_iso]

I'll toss in a few thoughts here.

Since using a recoder with XLR inputs seems to have solved the problem, and also eliminated the mics themselves as the main point of entry, it's likely the input style of the R5 that's the problem.

A couple of things about cameras with 3.5mm mini inputs vs XLR inputs. The R5 manual says the external mic jack is a "3.5mm diameter stereo mini jack". That tells us a whole lot. It first tells us that the jack provides two mic inputs, left and right. But it also tells us that the input is "unbalanced", meaning, there is one signal wire per input, and the shield acts as the return wire for both left and right. Any noise coming down the cable, regardless of how it got there, is mixed in with the mic audio. No noise immunity on an unbalanced input, and it doesn't matter a bit if your mic is XLR and balanced, the camera will unbalance it.

Compare that to an XLR input, which uses two signal wires and a shield. The mic audio is presented as a difference between the two signal wires, while noise and interference is carried equally on both signal wires. The XLR input looks only at the difference between the wires, and ignores whatever signals are common to both, and that provides a large degree of noise immunity. It's why pro audio and pro video cameras have XLR connectors on them, it's the noise immunity. And I'm afraid it's just one of the long list of reasons that a mirrorless or DSLR is really not a great video camera, even though they can shoot great video.

Another solution might be to convert your R5 input to a real balanced input. You can do that with a transformer (two for stereo). An audio transformer will have quite a bit of "common-mode rejection", the ability to ignore noise on both signal wires, while the transformer output can be a relatively short wire that connects to your 3.5mm jack. One easy way to get this done is with a mic splitter box, like the Whirlwind SP1X2, which provides one direct and one isolated output from your mic. The isolated output can be connected to your unbalanced R5 input, and the noise should be gone. Another device that would work is the Radial IC1 line isolator. When you wire from the XLR-M output to your 3.5mm input you have the opportunity to wire both channels together too, which might be sort of nice in post. The cable you want for that would be an XLR-F to "dual mono" 3.5mm TRS. Read the descriptions very carefully.

Either way, those should kill your noise without the complexity of using a separate recorder (an re-sync in post).

Just for future reference, ferrites actually do work as an RFI block on a cable, BUT...and it's a big one...the characteristics of the ferrite core have to match the frequencies of the interference, and most common ones are "tuned" for computer-type frequencies in the megahertz, rather than the switch-mode power supply frequencies found on LED drivers, which are in the 10s - 100s of kilohertz. Very, very few ferrites will work on those.

And also, for reference, once a cable is shielded, the difference between shield performance from one cable to another has very little impact on interference immunity. It's never ever going to be a day/night improvement. So trying other cables is usually wasted effort unless your original cable is broken or wired wrong.

 

[thomatkinson]

Thanks for those thoughts and suggestions - very interesting. I think you must be spot on that it's the R5 input causing the issue.

Good to know this about ferrites too. It was interesting to try it and useful to know about, but I don't think it's my solution.

At the moment, my workaround is using an external recorder. It's more of an upgrade than a workaround, because the sound is way better and the recorder I bought is 32bit float, which takes a lot of complication out of recording audio. The only disadvantage is having to sync audio in post, but that may be a good trade overall.

As mentioned before, I'd still like to have the option of ready synced audio via the R5 input. The suggestions you give for doing this sound good but a little unwieldy for many shooting situations.

The thing that is still frustrating me, is that there must be many R5 shooters who use LED lights exactly like mine. Are they all having problems or is it just me? I know several videographers working with various small mirrorless cameras and LED lights, and they don't have this problem.

Last ditch attempt to find a better solution:

Does anyone think this could be a fault with something? (Canon have been a bit unhelpful and blamed everyone else)

Does anyone think a different light would help? (Nanlite has been a bit unhelpful and blamed everyone else)

One thought - the 3.5mm adaptor cable which goes into the R5 mic input, has a coiled wire. Do you think this could be causing any problem?

Thanks again!

 

[low_iso]

Thanks for those thoughts and suggestions - very interesting. I think you must be spot on that it's the R5 input causing the issue.
Good to know this about ferrites too. It was interesting to try it and useful to know about, but I don't think it's my solution.
At the moment, my workaround is using an external recorder. It's more of an upgrade than a workaround, because the sound is way better and the recorder I bought is 32bit float, which takes a lot of complication out of recording audio.

Still be careful with levels. It may quantize at 32/float but no analog part of that system has anywhere near that kind of dynamic range or headroom. Mic preamps for example are all limited to around 18 bits of DR.

The only disadvantage is having to sync audio in post, but that may be a good trade overall.
As mentioned before, I'd still like to have the option of ready synced audio via the R5 input. The suggestions you give for doing this sound good but a little unwieldy for many shooting situations.
The thing that is still frustrating me, is that there must be many R5 shooters who use LED lights exactly like mine. Are they all having problems or is it just me? I know several videographers working with various small mirrorless cameras and LED lights, and they don't have this problem.

As a pro video guy for 25 years I simply can’t consider any still camera that shoots video good for anything but b-roll or second camera. Rent a good semi-pro video camera and you’ll see why.

Last ditch attempt to find a better solution:
Does anyone think this could be a fault with something? (Canon have been a bit unhelpful and blamed everyone else)

It’s a limitation of single-ended/unbalanced input design. Not a fault, a design choice.

Does anyone think a different light would help? (Nanlite has been a bit unhelpful and blamed everyone else)

Sure worth a try. All LED lights use drivers with switch-mode regulators, it depends on if the designer did his homework to keep RFI out of it.

One thought - the 3.5mm adaptor cable which goes into the R5 mic input, has a coiled wire. Do you think this could be causing any problem?

Nope.

Thanks again!