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hobosoundguy

audio and Timecode onto a goPro

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Hi guys,

i'm on a show with alot of driving so we have rigged one of the trucks with a timecode slate and i have split the audio input on the go pro's to put linear timecode on track 1 and scratch track audio on track 2.

Everything is powered of the truck through an inverter so we dont lose power.

we are also powering the gopro's off an inverter.

for some reason when we tested it this evening there was a colour grain on the gopro footage. it appears the timecode is freaking out the gopro's picture.

it seems unlikely but we've looked at most of the other components and it seems to be the only solution?

Why would audio freak out the video signal?

i have already padded the timecode down by 40 dB in case the signal was too strong.

any suggestions welcome

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Timecode is a nasty square wave signal. It gets into a lot of places it shouldn't. There's a possibility of the rate of the timecode pulse affecting some other part of the gopro's circuitry via itself or its harmonics.

If timecode is the culprit, and production absolutely needs to use this camera, then you need to get rid of the timecode. Remeber, they're not a "real" camera, and compromises have to be made.

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We've one hidden camera shows with 40+ go pros using just a TC slate and flashing it up in front them. It was a bit strange as the gopros were running at 30fps, and everything else at 25, but post had always done it like this and it seemed to work with some clever converting, I suppose.

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You might try our ERX2TCD receiver with time code output. The time code level is completely adjustable and it is bandwidth limited to the the audio range so the tc signal in not square. It should not interfere with the cameras video circuits.

You might also look at the inverter feeding the camera power to make sure it is clean. There might be a beat frequency problem between noise on the power and the video signal. You might need to filter the power.

It may also be a ground loop problem with the TC gen if the camera and the generator are working from the same power source. Isolating the TC gen to its own power source may do the trick.

Glenn

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If anyone has ever looked at the output of the voltage from a cheap power inverter on a scope, it is way nastier than what TC looks like and much higher voltage!!

I'll put a small amount of money on the problem being caused by dirty power. Cheap inverters are even KNOWN to cause problems in TV displays, why not cameras too?

Bellow you can see to waveforms, the first is from whats know as a "sudo-sine wave inverter", the second is a "true-sine wave" inverter and is a proper AC source.

post-2177-0-93453500-1357143159_thumb.jp

post-2177-0-56300900-1357143171_thumb.jp

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You could try putting a small cap across the timecode generator's output to round its wave. Most readers these days look for zero crosses, not square waves per se, so the timecode can look almost like a +/- triangle and still work. Do a test, of course...

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Unless you are really killing the GoPro's input with super duper hot levels (hot enough that the TC would be unreadable) then I'd suspect the DC powering of the cameras. I'd vote for using the camera's own batteries first, then a pure sine DC source, and the truck invertor maybe not at all unless it is pure sine. I would not want anything else on that DC line except cameras.

phil p

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Hi fella's,

Alas there is only one power source, the truck.

I have padded the timecode down by 40dB already. We're gonna test this evening and see if I putting another 30 dB does the trick.

I'm still convinced its a power problems but when we have the power into the goPros its fine. It's only when we plug power and timecode in it freaks.

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Hi fella's,

Alas there is only one power source, the truck.

I have padded the timecode down by 40dB already. We're gonna test this evening and see if I putting another 30 dB does the trick.

I'm still convinced its a power problems but when we have the power into the goPros its fine. It's only when we plug power and timecode in it freaks.

Follow Glenn's suggestion, try battery powering the GoPro, and plugging in TC. If the issue goes away, then it is indeed a 'beating' problem between the power and the tc signal.

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Does post have a good reason for needing linear timecode in addition to the timecode slate at the start of the file? The show I've been mixing for the past 11 months uses GoPros on a daily basis and we slate the top of the clip. We don't send audio or timecode to it (other than the slate) and there have been zero issues the entire show with syncing audio from the external recorder.

It just sounds to me like production is trying to come up with a $10 solution to a $1 problem?

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I do a show where there are a lot of gopros and non tc cameras involved. When the camera techs set them up they show the camera their iPhone (or the denecke tc app that I suggested) and call out the time. This has saved many many hours of money flying out the window via post. We dont bother with trying to put any audio into the cameras other than their on board mics because its really more of a waste of time for something we wont be using anyway.

I generally default to the rule that if we arent using a real camera with time code than I wont try to feed it into the camera as audio. It is merely an option production loses when they decide to use consumer cameras instead of professional ones.

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My bet is on the power source being the problem in your case. What are you recording to? What is your sound rig? Also does the camera get the audio clean without the timecode injection on what I'm guessing is a special build cable. Seems if they get a good scratch track to camera they don't really need the TC. Good luck.

CrewC

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Hi fella's,

Alas there is only one power source, the truck.

I have padded the timecode down by 40dB already. We're gonna test this evening and see if I putting another 30 dB does the trick.

I'm still convinced its a power problems but when we have the power into the goPros its fine. It's only when we plug power and timecode in it freaks.

If padding the TC down that much more makes the picture clean then GoPro has a serious design problem. TC recorded that low with such low quality analog input electronics may be hard to recover as accurate TC--you might want to check that as well. If the cameras HAVE to be powered by the truck, does the AUDIO gear have to be powered by it too--can it run on it's own battery? That would eliminate any nasty backflow through a shared DC system.

philp

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Hi fellas, thanks or all the heads ups

Basically we're working on a 5 month long gig for an emergency response crew. The directors do ride alongs with the truck drivers to wrecks.

In short we're trying to make a fool proof system where all the directors have to do is press record and all the parts role. We can get the call at any time and these guys don't wait. There are also many fools.

Basically everything has to run continuously or we get into having to change batteries regularly, regularly rejam, monitor etc and having to explain to directors as one man bands how to do things. From experience that just causes havoc and untold headaches for me when I'm already trying to do the job of 4 men.

The directors camera acts as the dialogue recorder. In it are the 2 wires for the 2 truckers. He sits in the back seat and shoots over the shoulder. The 2 go pros shoot singles.

I also have a tascam recording the radio chatter between the trucks in the ride along.

The timecode slate acts only as a generator of tc. If I leave it in the truck on its own batteries it runs the risk of dying or not being used or being kicks to death by the truckers.

I'm considering if I put a mix pre in I can adjust the balance between scratch track on the goPro's and timecode

But the main hope is that we can eliminate the ground loop that's effecting the picture in low light.

My timecode system in effect works. Unfortunately the damn goPros are freaking out.

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In short we're trying to make a fool proof system where all the directors have to do is press record and all the parts role. We can get the call at any time and these guys don't wait. There are also many fools.

This sounds like a train wreck of train wrecks.

I want a new T-shirt that says:

BEWARE OF PRODUCERS

WITH UNREALISTIC EXPECTATIONS!

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Hobo: why would you power a GoPro off an inverter? I have the older Hero (Hero1 I guess now), but isn't external power still through the mini-USB? I don't doubt that the overpowering TC signal could overload circuits, but you could also try it off the internal batteries and avoid the inverter.

I've powered them with cigarette-USB adapters intended for smartphone car charging. If nothing else you can easily get an isolated external battery that will power one for a day, and won't require the car/truck to be on to get power. I used one to set up a GoPro to shoot time lapses and kept it powered for 15+ hours.

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Hobo: why would you power a GoPro off an inverter? I have the older Hero (Hero1 I guess now), but isn't external power still through the mini-USB? I don't doubt that the overpowering TC signal could overload circuits, but you could also try it off the internal batteries and avoid the inverter.

I've powered them with cigarette-USB adapters intended for smartphone car charging. If nothing else you can easily get an isolated external battery that will power one for a day, and won't require the car/truck to be on to get power. I used one to set up a GoPro to shoot time lapses and kept it powered for 15+ hours.

we have the go pro powered off the truck so they are powered for 5 months. i'm running 20ft usb cables to the inverter. all hidden in the walls of the truck.

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after much testing and with much help from your suggestions by jov we've got her. (i think)

we upped the inverter to a 300w inverter which had a more stable wave although not completely curved it does the trick.

in saying that the main issue seems to have arisen from the usb ports on the inverter. the 150 watt one we were using had 2 plugs and 2 usb ports.

the tc slate and tascam power were on the plugs and i was powering the goPro's off of the 2 usb's. it appears they weren't as stable as advertised so on the bigger inverter we switched in ipod plug adapters and it seems to have fixed the problem.

one word of caution: even though i spent 2 days fixing the problem there is a chance that it may not have been my system at all that was causing the issue.

the camera's were set to narrow on hero2's and in low light they are very grainy all by themselves. there were also 2 camera's that were magically replaced without a reason why and new goPro 3's put in at just the same time as i adjusted all my rig.

I suspect there may have been a certain amount of "oh it must be the sound department" when in fact the camera boys weren't that sure of their own kits failings themselves.

sufficed to say the system now works. i know it sounds complicated but it works very well and post are wetting their pants with joy over it.

everything roles and pops in the edit stack and no one has to spend days syncing up 4 things at once with no sync clap after a director forgot to do it at 2am some random tuesday.

i have to say the system would be nothing without Dave Hable in Vancouver. my idea was an adaptation of a set up i found on another post but i could never have got it to work without dave's wiring. - the mans a miracle worker.

thanks as ever for the input.

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I suspect there may have been a certain amount of "oh it must be the sound department" when in fact the camera boys weren't that sure of their own kits failings themselves.

A new candidate for a T-shirt: "This is what happens when you use Toy Cameras on Real Productions!"

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also a heads up the new gopro hero 3 has done away with the headphone and everything, power, 3 outs and 2 audio ins are all on the same usb connection.

how that effects things we'll soon see.

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