Film-Tech Forum ARCHIVE: Roll Bars During Pre Show

This is topic Roll Bars During Pre Show in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Martin McCaffery (Member # 37) on 05-28-2013, 08:55 AM:

Went to the AMC (formerly Rave) Festival Plaza to see Iron Man. While they continue the Rave tradition of dim projection, and this is the first commercial theatre showing where I've ever felt like asking them to raise the volume, the most annoying thing was during the pre-show advertising-a-thon (even more annoying than the advertising--at least 3 ads for television shows!).

All through the pre-show, which appeared to be presented in 720, there were bars rolling up the screen. They weren't black bars, like on old TV's but regularly space "clear" bars, as if they were embossed on the image.

What were these, what caused them and how can I avoid them when we get digital?

Posted by Harold Hallikainen (Member # 5405) on 05-28-2013, 09:09 AM:

Sounds like hum bars. They might be using analog video and have a ground loop.

Harold

Posted by Jim Cassedy (Member # 4115) on 05-28-2013, 11:29 AM:

Definitely sounds like a video-ground-loop problem as Harold said.

quote: Martin McCaffery
how can I avoid them when we get digital

You should not have any problem when playing back digital content from your server,
but hum-bars sometimes occur when interfacing analog equipment. (BluRay, DVD, etc)

Most common way to fix it is to buy a "video-humbucker" box. They come in both active
(opto-isolated) and transformer coupled versions, and sell for abt $50-$200 depending
on type & quality. It's a good device to have on hand anyway. I have a semi-professional
one with both RCA and BNC video connectors on it that I keep in my "bag of tricks".

It cost me about $150(us), and is worth every penny. It has more than paid for
itself by saving time, labor & head-banging when trying to track down vexing video
ground loop problems while attempting to interface 'outside' equipment into our system.

Since one of the facilities I work at is often used for corporate events, I've often
got to hook "client provided" equipment into our system, so I've even got a
"VGA Isolator" - which has cured a lot of problems when connecting up a client's
computer to the system over a long cable for their power-point presentations, etc.

Depending on the nature of your business and how much 'interconnecting' you'll
be doing, you may or may not need any of this. But I've found the extra
equpment to be a good investment in my particular projection situation.

"I'm just sayin'......

Posted by Martin McCaffery (Member # 37) on 05-29-2013, 10:29 AM:

There will be much interconnecting in our future. Thanks for the info and tips.

Posted by Joe Redifer (Member # 3) on 05-29-2013, 08:56 PM:

quote: Martin McCaffery
All through the pre-show, which appeared to be presented in 720

Highly doubtful. Probably 480p.

Posted by Martin McCaffery (Member # 37) on 05-31-2013, 08:01 PM:

Whichever, looked like crap. [Wink]