Catalyst hum issues video hum on SD composite capture
Posted 24 February 2012 - 10:50 AM
Unfortunately no one wants to own this problem, which is hard to pin down as timecode comes from audio, via the lihgting desk, so all 3 departments - audio, video and lighting- are saying its not me...
I currently have both opto-isolator and transformer hum killers on my composite video lines and yet we still get hum on the cat inputs, which of course are fine until the show starts - there is no hum whatsoever on my SD video system . The signal only goes a few meters and there are no mains cables nearby. I've tried taking my power from both the lighting and video racks to no avail.. The hum spikes when the kick drum hits ( audio) but also when the strobes fire ( lights)??
needless to say, we did a US tour in october with no problems whatsoever - those cats were supplied by a US firm.
I am totally at a loss as to how to solve this. I've considered converting to SDI from my rack to the catalyst, but even that wont solve hum will it??
and it still wont solve the massive hum on the timecode line, which again couldn't be dealt with by hum eliminators.
I suspect its a problem in the catalyst rack itself.
as an aside, we had enormous problems with the catalysts at production rehearsals.
it turned out they were running PAL as drop frame???
the only way around this was to overclock the PAL by 0.04 of a second to bring the sync back in.. you ever heard of this before??
tried the catalyst forums, but cant get on and the admin are not responding
currently doing onstage video for Duran Duran
Posted 24 February 2012 - 04:17 PM
Unfortunately no one wants to own this problem
There's a surprise!
Might be worth a try, as long as the hum's not already there when you do the conversion, turning the analogue signal into digits should cure it.
Posted 24 February 2012 - 06:25 PM
A couple of questions for you
Hum on the timecode line to the Hog - not Catalyst related, but, are you using SMPTE? What is the source for that? All cables good from the source to you? What is the distance to the source? Have you tested the line with a stand along timecode reader to see if the signal is ok?
Composite lines - again, how far is the source(s)
How many sources?
What are the sources?
Is the cable good quality coax?
Have you put a good quality monitor on the end of the cable going into the capture card to see if the hum is there?
Posted 24 February 2012 - 10:56 PM
as for the composite.
was totally fine my end, and the last thing between video out and the catalyst in was a monitor and the cables are very short..
tried everything but couldn't cure it and don't really want to be in that situation again.
Like I said, it was fine in the states on a different catalyst machine..
Posted 25 February 2012 - 01:36 AM
Sorry to giggle, but it's hard to imagine a much bigger clue than that, normally its not that obvious.
Although it's not the sound guys fault, a decent sound guy would be used to issues like this and would have stepped up to the plate to help.
This isn't the right answer but will get you going.
If you disconnect incoming composiuve video and timecode cables is the world OK? If so, that narrows down the problem.
Is the timecode MIDI time code or SMPTE audio time code? I suspect the latter because MIDI is already opto-isolated so get a transformer isolator on the audio feed. Sound should have one.
DOne that, and the composite lines (from cameras?) already humbugged? Then somehow you're getting a loop before the humbug. Take it one line as a time, and find out where the issue is. Try a humbug at each end of the CV cable.
What I actually think is wrong is a problem in the power system, a neutral-earth bond somewhere there shouldn't be, but that'll take some effort and be quite disruptive to all departments to track down, and if there is such a bond and the production electrician hasn't been helpful so far, then you may be out of luck anyway. The reason is that as the load on te power system increases the symptoms get worse. Thus the issue is increasing voltage drop across the neutral conductor(s) getting superimposed on relative earth potentials in a way they just shouldn't.
As a final desperation, assuming the timecode feed is ungrounded and clean as above, do your own power distibution; plug in your kit to the same place the (presumably) big screen is plugged into, and then distribute power to the cameras alongside the CV coax.
I (still) love Druan Duran, so you need to make it work for the people!!! Saw their first gig as a reformed band, which was (of all places!) here in New Zealand supporting Robbie Williams a few years back, that was a good day.
Website: http://www.davidbuckley.name, a good place to go for PCStage tips and techniques
Posted 25 February 2012 - 09:42 AM
I think you are in a start again situation , run the server from the same distro as the video and get the mains checked. If its clean on content only from the cat itself connect a dvd or similar to the video ins if thats clean connect your composite lines , if thats clean the artnet, then the timecode etc. At some point its going to break and you can then try isolating things either by humuckers, opto isolators or fibre.
I susspect that its only your problem as you dont notice the symptoms on the sound system so it must be you. You say it was a different cat rack in the states, but im asssuming it was also a different sound supplier and for that matter the US mains is different. Very similar to all the arguments you used to have about the lights making dimmer noise through the pa, who was at fault - the lights for causing the intererence, the pa for not being better shielded or the venue for having a substandard earth?
Posted 25 February 2012 - 10:51 AM
I think we all concur and of course this is exactly what you get when you dont have sufficient time at production rehearsals.
just to answer a couple of the questions, yes we run EBU but we only had serious LTC problems once, though there was an isolation transformer on the line running into the whole hog as the timecode was breaking up in rehearsals.
as for the composite feeds, they were opto isolated on the line out from my system and also transformer isolated at the catalyst end, but this made very little difference to the hum onscreen.
I;ve had situations like this before where you get a voltage so big that the isolators cant handle it, so maybe that was what was going on.
Next time we'll meter all the system earths through if we get issues, but these days, time at production rehearsals is pretty much non existant.
Posted 27 February 2012 - 09:16 PM
>as for the composite feeds, they were opto isolated on the line out from my system and also transformer isolated at the catalyst end, >but this made very little difference to the hum onscreen.
>I;ve had situations like this before where you get a voltage so big that the isolators cant handle it, so maybe that was what was going >on.
>Next time we'll meter all the system earths through if we get issues, but these days, time at production rehearsals is pretty much non >existant.
Just to add my two'pennorth of queries: Are you describing an audio problem of "Hum" or a video image problem (wiggly images etc)" as it seems a little ambiguous from your post I.e. "Hum on screen".
Also reading your posts are you seeing this problem with feeds input to the Catalyst and then output to display?
I ask as if your problems are relating to the recent rescheduled European Duran Duran tour, I happen to have the same setup sitting not 10ft away, in fact the same boxes, the same consoles and little further away the same LD.
I have SDi camera feeds into the catalyst, output from it via Fulsom image pro, Catalyst power from Video mains, Artnet control form Hog via lighting data network and EBU from FoH Audio console, audio also have a stereo mini-jack from the back of catalyst, so plenty of room for mixed and matched earth loops!
let me know and I'll see if I can help.
Posted 01 March 2012 - 11:52 AM
yes it was the Euro DD tour.
I was describing both audio hum, on the timecode line and video Hum on the screen - rolling bars and break up of image in lines.
Vince told me the system works fine with your configuration, although if the cause was something like the motor control or a lighting fixture, then its highly likely you wont get the same problem.
maybe that takes the catalyst out of the equation, though previously it was run from Lighting mains - also it looks like you have different capture cards..?
guess, we wont know until we roll back out on the road.
This post has been edited by deepvisual: 01 March 2012 - 11:53 AM