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Interference type issue with Sennheiser G3 kit

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Joe Bressler
Interference type issue with Sennheiser G3 kit
on Jul 6, 2015 at 1:40:01 am

Hello,

I just finished a shoot that utilized two Sennheiser ew100-G3 lav's. On both sets I performed a scan, used the bank with the most open channels, and synced the transmitter to the receiver without a problem. The transmitter was placed in the subjects pocket.

example: https://vimeo.com/132673631
password: senny

Despite this I still was having serious problems with this type of interference throughout the shoot. Can anyone give me some ideas to try as far as fixing this issue for future shoots? Of note: the subject was carrying a radio and his cell phone was in the same pocket at the transmitter for a period of time. Changing this had no effect and I have had this problem on another shoot in a completely different location in a completely different environment. Further, in my tests indoors at home I have not run into this issue, it is only when outside on walk and talk style shoots that I get this issue.

Can anyone shed any light on this for me? What am I doing wrong? It seems like it would have to do with subject movement since I cannot replicate it in my tests and since it has happened in two different locations, urban and rural/suburban.

Thanks in advance for your help.

-Joe


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Ty Ford
Re: Interference type issue with Sennheiser G3 kit
on Jul 6, 2015 at 2:17:22 am

Hello Joe and welcome to the Cow Audio Forum.

Sorry for your pain.

Sounds like an RF problem. What shape are your transmitting and receiving antennae? Are their connections to the transmitter and receivers solid? If one or the other of them has pulled off the circuit board inside, it could do this.

Can you operate them without this problem in other locations with the same sort of conditions. In pocket, etc.?

Were both wireless mics doing this?

Where were the receivers?

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Joe Bressler
Re: Interference type issue with Sennheiser G3 kit
on Jul 6, 2015 at 2:51:04 am
Last Edited By Joe Bressler on Jul 6, 2015 at 2:53:03 am

Hi Ty,

All antennae were straight and the receivers were both mounted on the camera rig.

I had another shoot where I used the sennheisers with the same problem. I had tested them before that shoot and had also tested them again before this shoot, but not in similar conditions. They worked fine in stationary, no-stress tests. However after this shoot I tried to test them again walking around outside with the receiver in pocket by myself, trying to get the issue to present itself, but I don't really think it's the same.

BOTH mic's were doing this.

Thanks for your quick response!

-Joe


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Peter Groom
Re: Interference type issue with Sennheiser G3 kit
on Jul 6, 2015 at 9:39:46 am

HI - to my ear there were 2 different issues.
The 1st problem in the start of the clip sounds more like a physical issue. So the mic cable, or the mic plug, or the socket, or a dry solder joint etc etc. It seems related to movement / paces.

Then I hear RF interference issues on the laster part which i agree with Ty on.

How come you didnt hear it as soon as it occurred and then address / adjust / fix before proceeding.
You were wearing headphones I presume?

In a city like NY you really have to be presuming that there WILL be issues around the corner so listening and adjusting constantly.
Peter

Post Production Dubbing Mixer


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Joe Bressler
Re: Interference type issue with Sennheiser G3 kit
on Jul 6, 2015 at 10:35:26 am

Hi Peter,

Thanks for your response. What could be done to reduce RF interference besides doing the channel scan and using the bank with the most free channels? We hadn't changed locations since the initial scan.

Understand nyc would be prone to rf interference but the exact same issue has presented itself outside of the city. Would changing the squelch help?

Thanks
-Joe


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Ty Ford
Re: Interference type issue with Sennheiser G3 kit
on Jul 6, 2015 at 12:34:18 pm

Joe,

Yes the antennae may be straight, but are they still soldered to the circuit board inside the transmitter and receiver?

Is there anything else on your camera rig when this happens?

Like an external monitor or monitor/recorder?

Regards,

Ty Ford
Cow Audio Forum leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Peter Groom
Re: Interference type issue with Sennheiser G3 kit
on Jul 6, 2015 at 12:42:37 pm

Hi
Im far from an expert when it comes to radio interference, but I can tell you that the best solution is to wear headphones.
If Im directing, and i see the sound man take his cans off, I stop and ask him why. Its crucial that people listen continuoulsly, just like the camera man watches throught.

In the UK only 1 bank is allowed by law. I cant speak for anywhere else but were you definitely working within the correct frequency set for your territory.
were all mobile phones turned off anywhere near?

Peter

Post Production Dubbing Mixer


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Joe Bressler
Re: Interference type issue with Sennheiser G3 kit
on Jul 6, 2015 at 1:02:35 pm

Hey all,

Thanks so much for your continuous advice on this. The rig was an a7s with XLR adaptor plugged into the shoe, with the two recievers mounted by Velcro on a movcam cage. I was monitoring sound, and stopped to fiddle with the system upon hearing the issue, but it was quite intermittent and like I said I don't know what adjustments to make besides finding a clear channel.

The talent was holding a radio and had his cell phone on. This sounds like hell for a radio mic system so I would imagine that wasn't helping.

The transmitter and receiver that I had been using were pretty much brand new units. Used only once before, with the same issue. So I doubt that the antennae had become un-soldered. Additionally oddly enough the rental transmitter was causing the most problems and was switched from the main talent to his buddy who was also mic'ed but was not speaking much.

How can I find out what frequency I should be operating within in my region?

Thanks again
-Joe


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Peter Groom
Re: Interference type issue with Sennheiser G3 kit
on Jul 6, 2015 at 2:59:27 pm

In the Uk it would be who you pay for your permission to use a radio mic. Theyre all licensed.
peter

Post Production Dubbing Mixer


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John Fishback
Re: Interference type issue with Sennheiser G3 kit
on Jul 6, 2015 at 5:03:24 pm

Try this link to Sennheiser's Frequency Finder. It may help. As stated earlier, NYC is awash in rf traffic.


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Tom Salyer
Re: Interference type issue with Sennheiser G3 kit
on Aug 6, 2015 at 3:10:05 am

I work with four sets of Senn G3 wireless and your type of zzzzt zzzzt RF interference happens to me from time to time even though I've scanned and set up on a clear frequency block.

Once I check to see the antennas are not against bare sweaty skin and I check all cable connections, I seem to fix it by simply opening up the receiver and choosing another clear scanned block.

It's awkward after wiring somebody up and listening to a clear signal, to have the subject walk 30 feet way and the zzzzt start ... but I'd rather go right back to them and quickly hop up a frequency block or two than convince my producer ghosts messed up his tracks.


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Ty Ford
Re: Interference type issue with Sennheiser G3 kit
on Aug 6, 2015 at 11:45:54 am

The thing about "clear" frequency blocks is that they may or may not be clear.

The interfering signal may be intermittent. So you scan, and in that moment it's clear. 43 seconds later something changes and you get a hit. You may never get another one on the frequency the rest of the day or you may get one every once in a while.

Even if you jump up a block and find a new frequency that appears clear at the moment you scan it, there may still be intermittent traffic on it as well.

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Joe Bressler
Re: Interference type issue with Sennheiser G3 kit
on Aug 8, 2015 at 8:30:03 pm

I have noticed in several situations that I will scan for a new list of available frequencies and find that there are several banks with available free channels.

Then i will run into RF interference, scan again, and notice that there are zero banks with any free channels.

Is this explainable? Really starting to think I have a bad kit here with how unreliable these units are. I know that occasionally you have to scan for new frequencies to use especially when changing locations, but I am finding myself with the devices set up properly, in one location, and facing RF hits constantly. It is not practical to switch channels several times during a shoot sometimes.


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Ty Ford
Re: Interference type issue with Sennheiser G3 kit
on Aug 8, 2015 at 8:45:44 pm

Hi Joe,

Please go back and read my last response. It answers your question.

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Joe Bressler
Re: Interference type issue with Sennheiser G3 kit
on Jun 15, 2016 at 9:29:58 pm

Hey all,

A little update to this story. I have been using the Sennheiser system with the receiver mounted off of the camera (with this setup) with much better results as of the last writing here. I've also used other Sennheiser systems with other a7s rigs flawlessly (albeit not mounted to camera) (30 interviews in 3 nights with not one RF hit). I've used this system with c300, mounted to camera, no RF hits.

After a call to Sennheiser tech support we determined that my particular camera was acting as an RF antenna that was causing the afore mentioned interference based on this test:

Just camera and cage set up and turned on. Receiver turned on. Receiver exhibits a little bit of RF on the display. When moved away from camera RF goes down and then out completely

Camera, cage, rails, monitor and shotgun mic attached, same behavior only a little more RF is present when the receiver is close to the rig than before.

With the same setup as above, I scanned a new list with the receiver mounted to the camera with squelch on low. No free channels usable.

My question is: are there any a7s users who have had this problem before? Is there a setting on the camera that I can change to stop this from happening (it's on airplane mode)? Do I need to get a new camera??? This happens regardless of what monitor is bolted to the rig, and I have also noticed strange feedback on sound coming from my rode videomic plugged straight into camera as well.

I want to be able to mount the receiver on or near the camera like I am supposed to be able to and (within reason) not have to worry so much about it!

Thanks for your advice in advance!


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Roger Van Duyn
Re: Interference type issue with Sennheiser G3 kit
on Jun 16, 2016 at 2:21:42 pm

This is might be slightly off topic, but the last post mentioned an unexpected source of rf interference, his camera. A few days ago while filming a deposition, I ran into a new source of rf interference with my setup. It was intermittent, and weak, but I could hear it through the headphones. I had a hunch it was something in the very close by, coming in and out of range. Probably in the same room.

So I started trying to figure out where it was coming from. All of us had turned off our cell phones. And there was nothing else in the room but me and my gear, the court reporter and her "typing thing" connected to a laptop. The two attorneys, the doctor giving the deposition, and four chairs. Then I heard the faint buzz again, when the doctor's wrist moved next to the lavalier microphone. Then the next time his wrist got near the mic, it happened again. He was wearing an Apple Watch. I think the watch was trying to connect to his I-phone or something.

When I started working on the footage, the interference wasn't audible. But it was audible in my headphones.

Lots of new challenges out there.

Roger


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Joe Bressler
Re: Interference type issue with Sennheiser G3 kit
on Jun 16, 2016 at 2:29:48 pm

OK check it out. I got to the bottom of the problem but now I don't know how to solve it.

After systematically taking apart the rig and checking how the receiver behaved after the removal of each individual component I finally got to the last three bits: the camera body, the metabones speedbooster, and the canon 24-105. With all three together there was the same RF behavior as before, but after the lens was removed, the RF dropped off and there was no longer an issue! I've also noticed that when the camera is powered on and the lens "engages" there is an RF spike and then it returns to about 1/3-2/3 filled on the display.

Any ideas?


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Ty Ford
Re: Interference type issue with Sennheiser G3 kit
on Jun 16, 2016 at 3:19:41 pm

Wow, Roger,

Thanks for bringing this up. So it was in the headphones but had bypassed the actual recording?

How does THAT happen unless the interference was only on the unbalanced headphone circuit?

How could it get there without first hitting the mic input? Was the mic a balanced mic plugged into a balanced input?

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Roger Van Duyn
Re: Interference type issue with Sennheiser G3 kit
on Jun 16, 2016 at 4:02:09 pm

My wireless kit isn't the greatest, but it's been adequate for the type of jobs I do. It has three Azden 35BT UHF transmitters with 310 Receiver and an even older twin (non-diversity) receiver. Like you mentioned, the transmitters all have unbalanced microphone connections.

The receivers have balanced xlr connectors that connect to my mixer, a vintage Shure M-267 I actually repainted a few weeks ago. Then an xlr output from the mixer connects to the camera. So, the sound was probably bleeding through the unbalanced cables themselves? Makes sense. I was about 4 feet away from the doctor. The sound only happened when the watch was a few inches from the mic.

As an aside, I found a funny looking device called a "tripod basket" that Manfrotto used to make years ago when the old video cameras all had separate recorders. It's the right size for the mixer, and everything mounts on the tripod legs. I have a 4 connection (color coded and number) xlr snake cable coming out the back of the mixer that I connect all the receivers to. Almost all the depositions I've filmed have been in small rooms. Once the room was so small that I had to film through the doorway, and I'd just cobbled together the tripod setup the day before.

Here's how the setup looks:



Roger


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