MattinSTL Posted November 15, 2012 Report Share Posted November 15, 2012 So today I'm convinced that one of the lights is pumping EMI into my lav channel... but I also hear it very faintly on boom. I moved dimmers and played around with placement on the breaks... could never beat the mysterious EMI... or RFI... wasn't sure... but that's what it sounded like. Ended up pulling the snake on the cam... and that did it. How often do you see this? I've heard crap feeds back from cams... but it didn't matter if I was on return or not... even on the recorder the buzz was omnipresent as long as I was connected to the cam(?) Quote Link to comment Share on other sites More sharing options...
Max Hirtenstein Posted November 15, 2012 Report Share Posted November 15, 2012 what camera? was it sending +48v? Quote Link to comment Share on other sites More sharing options...
MattinSTL Posted November 15, 2012 Author Report Share Posted November 15, 2012 This was a shoot for a significant cable network (I'd rather not say, not sure if they'd expect me to fix the cam ground loop... but I tried)... it was on a small cam... Sony 7ZU. Of course I made sure it wasn't sending phantom (on my line-in)... I also re-routed my cables and rigged them so nothing was even touching the camera... didn't matter. I was torn on rigging everything wireless at that point... just to try it, but the day was moving fast and I'm confident they got good usable sound... perfect sound on the boom channel... and acceptable (with a little post work) on the lav channel... but I wasn't in the best mood by the end of the day... thinking, damn, it's always something. (for the record, I usually get really clean sound... I'm just saying that IN LIFE... "it's always something".) Quote Link to comment Share on other sites More sharing options...
Sndspd Posted November 15, 2012 Report Share Posted November 15, 2012 Was the camera on AC or DC? Was there a monitor connected to the camera? And if so, was the monitor AC or DC? Were either 2 plugged into the same circuit as the lights? Gabe Quote Link to comment Share on other sites More sharing options...
Jack Norflus Posted November 15, 2012 Report Share Posted November 15, 2012 This has been discussed here before. Basically there are probably 50 different things that can cause this. One thing that could possibly help is something like a Sescom IL-19. But of course "it depends". Quote Link to comment Share on other sites More sharing options...
MattinSTL Posted November 15, 2012 Author Report Share Posted November 15, 2012 Was the camera on AC or DC? Was there a monitor connected to the camera? And if so, was the monitor AC or DC? Were either 2 plugged into the same circuit as the lights? Gabe There was a little TV Logic monitor on top of the cam... and a BNC leading out to the standard Panasonic 17" monitor that everyone uses. The Panasonic monitor was AC, but even the TV Logic was on batteries... so... the BNC was the only way for a problem to get to the cam(?) I figure there must have been a problem with the cam itself, BUT... the Panasonic was plugged into a cube tap... as far as I could see, the only other thing plugged into that was iPhone chargers and a laptop. Quote Link to comment Share on other sites More sharing options...
Jon Gilbert Posted November 15, 2012 Report Share Posted November 15, 2012 I'd unplug the iPhone chargers next time, No1 suspect! Quote Link to comment Share on other sites More sharing options...
MattinSTL Posted November 15, 2012 Author Report Share Posted November 15, 2012 I'll be back on this shoot today... so I'm going to try that. Also... this is a skeleton crew that travels the country doing local stories for a national show... so you wouldn't think this would be the first time they've heard of this. I'm going to feel weird solving a problem today, that would have been MUCH better solved yesterday... at the START of the day... but honestly I thought it was one of the lights (and it still might be)... a 2K started buzzing half-way through the day yesterday... and a few flicks on the back of it quieted it down. Funny... it's a new client for me... and I expected to blow them away with a perfect job... well... it sounded good, but the lav channel is going to need some post. I'm assuming they'll either use the boom... or they'll sample the room-tone... complete with buzz... and be able to take it out. The buzz was about -25db to -30db... i.e. it kept the first light of my 442 lit the entire time on that channel... I'm guessing having that buzz 20db below peaks is probably fine... but by the end of the day I was exhausted from worry that it wasn't. I gave out G2s for coms... so they had a clear ear on what I heard. *shrug* I'll try unplugging some stuff today... and also get another stinger dedicated to ONLY the Panasonic monitor. If that fixes the issue I don't know if I'll be happy or depressed. We shot for 13 hours yesterday... and for the first 6 hours I was convinced it was the lights... which I could HEAR buzzing when I got close to them... so again... it might still be that. Either way... I'll know the answer today. Quote Link to comment Share on other sites More sharing options...
jacefivesound Posted November 15, 2012 Report Share Posted November 15, 2012 Where was the camera from? When we did Project Runway we used cameras from Wexler Video (no relation to our host) and their cameras were not internally grounded correctly. Somehow they found a way to blame us for causing the problem AND they sent techs out to fix the problem they clearly caused... while blaming us. Terrible company. Quote Link to comment Share on other sites More sharing options...
MattinSTL Posted November 15, 2012 Author Report Share Posted November 15, 2012 The other crew is out of NY... I figured it must be their cam. I have no idea why you'd fly across the country and rent a small cam. I'm going to trouble-shoot the cube tap and get a dedicated stinger on the monitor first thing... if that fixes it... well... it will only add to my value next time... because I figure this can't be very common. I read somebody's comment (or signature) recently... stating that 50% of a sound guy's job is problem solving... that thought kept ringing in my ears along with the buzz all day yesterday. I did a gig in Austin a while back... and they told me the post guy actually commented that the location sound basically didn't need anything... that he was surprised how clean it was compared to what he was used to... I was really hoping to get that result with a brand new client... especially out of NY... they should be happy... but I know it could have been better. (Like I said, I may try all that and still have the buzz... at this point I'm ASSUMING, based on deduction and experimenting... that it's a ground loop originating at, or in, the cam). Quote Link to comment Share on other sites More sharing options...
jacefivesound Posted November 15, 2012 Report Share Posted November 15, 2012 I guess my only confusion is where the camera is from? If it's near where you're shooting I'd have the rental company replace it. Whatever is happening is almost certainly a camera problem of some sort that will need to be fixed internally. If it's faulty gear, they should replace it. Quote Link to comment Share on other sites More sharing options...
Geoff Tirrell Posted November 15, 2012 Report Share Posted November 15, 2012 I would check the little monitor. I know a lot of cam guys who don't always use a broadcast quality monitor for confidence or non critical framing. The problem is these things don't have things like built in protection from ground loops that some of the higher dollar monitors have. I was actually on a shoot where the 2nd cam was running one of these and it bled back into my system as soon as we hit record... did not hear a thing before then. The real beast of it he refused to admit that it could be coming from his end until nearly 40 minutes later when we had tried everything else in the book to kill that hum. It is actually a text book case for how something at the end of the production chain can cause technical difficulties for something at the beginning. Quote Link to comment Share on other sites More sharing options...
MattinSTL Posted November 15, 2012 Author Report Share Posted November 15, 2012 Geoff... it's a TV Logic monitor... I don't know if that counts as high-end... but it's definitely not low-end! Let me put it this way... it's got a color waveform on it... $$$$. I'm glad to get the support I have on this issue so far... I was hoping to get some similar experiences related to the situation. The nice thing about this thread is I'll be able to zip it up tonight or tomorrow with the results of the day... then hopefully in the future if somebody searches "ground loop" they will find this thread and save themselves a headache. Quote Link to comment Share on other sites More sharing options...
Derek H Posted November 15, 2012 Report Share Posted November 15, 2012 Alright now.. Are you sure the buzz is actually being recorded? If you haven't yet do a playback test. Also, is the buzz just on your return signal or are you hearing it even when listening to your mixer directly? ..I had a buzz come in on my return once but it was not present on tape. May also be worth taking a look inside your xlrs on the snake to see if they are wired with pin 1 to shell. If so snipping that may eliminate it... Or not! Good luck! Quote Link to comment Share on other sites More sharing options...
Scott Smith Posted November 15, 2012 Report Share Posted November 15, 2012 Happens a lot. Have you tried inserting a transformer on the feed to the camera? (Something like a Secom IL-19 would suffice, even though it's not great quality). If it eliminates the hum/buzz, then you know you've got a ground loop. If it doesn't the problem is somewhere else. You don't make mention of what kind of mixer or cable system you have. I assume you are running on battery? Quote Link to comment Share on other sites More sharing options...
studiomprd Posted November 15, 2012 Report Share Posted November 15, 2012 (edited) " One thing that could possibly help is something like a Sescom IL-19. " an industry standard for this sort of issue for many years... also required in a thorough kit are some pin-1 (ground) lift XLR adapters ... Edited November 15, 2012 by studiomprd Quote Link to comment Share on other sites More sharing options...
Geoff Tirrell Posted November 15, 2012 Report Share Posted November 15, 2012 " One thing that could possibly help is something like a Sescom IL-19. " an industry standard for this sort of issue for many years... also required in a thorough kit are some pin-1 (ground) lift adapters ... Yes me personally I would have started there with ground lifting my way down the record chain until I find the offending cord, outlet etc... Quote Link to comment Share on other sites More sharing options...
studiomprd Posted November 15, 2012 Report Share Posted November 15, 2012 " with ground lifting " I would have started, and probably ended with ground lifting and/or transformer (IL-19, http://www.sescom.com/product.asp?item=IL-19) isolation of my audio connections to the rest of the world; another option is to disconnect all cables and go 100% wireless. AC power ground lifting may lead to safety issues. Quote Link to comment Share on other sites More sharing options...
MattinSTL Posted November 16, 2012 Author Report Share Posted November 16, 2012 I thought about going full wireless, but didn't have enough units for talent and hops... plus, it seemed like some locations were worse than others... or maybe the louder talking parts of the day masked it better because the overall levels were lower as voices were louder. Verdict? It was the camera... or the combo of the TV Logic and cam. I played back my audio and it's definitely clean enough... that was a good call asking if it was being recorded. It wasn't nearly as offensive in the recording as it was direct through the mixer... This was 442 with a beta-snake (mogami) leading to a Sony 7zu. Today I told the producer about the issue... and she said another audio guy deduced the same thing. That sentence alone was total relief for me... because if anybody mentions the low hum... that's going to be my quote of the day. Ironically... a "normal shoot" is never the norm... Whatever... gig over. Client happy... beers being consumed. By the last half of the day I did go as wireless as I could... made a leg belt out of gaff at the last second... after a wardrobe change that left no mounting options... used gaff sticky side out... with just a slight bit of give... but tight enough to stay on the top side of the calf... then stuck another wrap of gaff to that... so that nothing was sticking to her leg... yet it made a custom fit leg belt which the Lectro clipped right onto and never moved... screw those professional leg mounts! "pop" goes the next beer... It was a good day. Thanks for the tips on the ground issue guys... looks like I need to get that Sescom bit in my kit. Quote Link to comment Share on other sites More sharing options...
Marc Wielage Posted November 16, 2012 Report Share Posted November 16, 2012 Verdict? It was the camera... or the combo of the TV Logic and cam. I played back my audio and it's definitely clean enough... that was a good call asking if it was being recorded. It wasn't nearly as offensive in the recording as it was direct through the mixer... That's good. I have encountered wired monitor situations where the last link in the chain went to AC, and that induced hum going back to camera. Same deal if they take an HDMI output and shove it into a computer... and the computer is hooked up to AC. Hum went away if the computer was solely on internal batteries. ...yet it made a custom fit leg belt which the Lectro clipped right onto and never moved... screw those professional leg mounts! I would be lost without a half-dozen sizes of Neopax waist belts and thigh belts! Those come in very handy, especially on very thin or barely-clothed actors, where there isn't a lot of costume to clip a transmitter to. The people I work with would not put up with gaffer tape, especially shoved near their nether regions. Quote Link to comment Share on other sites More sharing options...
MattinSTL Posted November 16, 2012 Author Report Share Posted November 16, 2012 I would be lost without a half-dozen sizes of Neopax waist belts and thigh belts! Those come in very handy, especially on very thin or barely-clothed actors, where there isn't a lot of costume to clip a transmitter to. The people I work with would not put up with gaffer tape, especially shoved near their nether regions. FTR, there was nothing STUCK to the actor... and I didn't have a thigh belt. She had on skin-tight jeans and I mounted the TX above her calf, but below her knee When I realized I had no mounting options due to wardrobe... and nothing with me for a leg mount... I was pretty happy with my solution and she said it was comfortable... and it never moved. I call that a win. Years ago I made something like the Neopax out of Ace Bandage... and the damn things kept sliding down the leg unless I made 'em super tight. Do the Neopax belts slide easily on the skin or do you just put 'em on pretty tight? Quote Link to comment Share on other sites More sharing options...
Marc Wielage Posted November 17, 2012 Report Share Posted November 17, 2012 The Neopax have always held OK for me, except if they actor is doing heavy exertion. In that case, I use SuperGlue! Quote Link to comment Share on other sites More sharing options...
RPSharman Posted November 17, 2012 Report Share Posted November 17, 2012 The Neopax have always held OK for me, except if they actor is doing heavy exertion. In that case, I use SuperGlue! Or staple gun. Quote Link to comment Share on other sites More sharing options...
Jon Gilbert Posted November 17, 2012 Report Share Posted November 17, 2012 The staple gun has only failed me once, then I used the nail gun I keep in the car for emergencies. Quote Link to comment Share on other sites More sharing options...
Rick Reineke Posted November 18, 2012 Report Share Posted November 18, 2012 I always go to the venerable IL-19s (iso transformers) for ground loop issues, however EMI can be caused by running A/C along side audio cables, especially mic level. In that case an iso transformer would do little. Quote Link to comment Share on other sites More sharing options...
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