Using color bars at the head of the tape

[David Morgan]

OK, At the risk of embarrassing myself, will someone explain this? If I put bars and tone at the head of each tape, what does it really accomplish? If the bars are generated by an internal generator and not something that is interpreted by the CCD's, then what for? A vector scope would show perfect everytime, unless there was something wrong with the generator.

[Brian Drysdale]

It's to check that everything is correctly lined up along a signal chain. In more more complex systems the video signal can be sent through quite a complex distribution system, like satellite links and routers, having the line up allows the engineers to see if there's an issue and correct it.

It's also handy in that you usually don't record programme material in the first 30 secs, a part of the tape that more likely to have drop out.

[David Morgan]

I understand about the signal chain business when doing a production but other than a filler, I suppose it's one partial indication that the cameras recording circuits are decoding or laying down the colors with the right information to tape. ?

[Andy Tejral]

Originally Posted by David Morgan

If the bars are generated by an internal generator and not something that is interpreted by the CCD's, then what for? A vector scope would show perfect everytime, unless there was something wrong with the generator.

Are you talking about camera bars at the beginning of a field tape?

Well, in a real camera--I know this is the case for Sony DXC-537 & 637: the color bars go through the same color encoder as the CCDs. So yes, the color bars will tell you if the camera color encoder through the tape transport are working properly. Really, there isn't much that can go wrong with the CCDs. If they fail, they fail pretty catastrophically.

This guy was doing a news story at base camp on Mt. McKinley. A helicopter landed and kicked up a lot of snow. The photog shielded the camera as best he could but moisture got in either through the lens or case of the camera and destroyed the CCD block.

Or, drop the camera on the lens and take out the CCD block that way. They actually epoxied the thing back together and it worked but certainly wouldn't sustain another hit.

Now, the 'el cheapo' cameras that most of us use? All bets are off because I suspect most of them do use a stand alone bar generator that does not go through the encoder.

So to answer your question, putting camera bars at the head of a field tape is somewhat outdated in the world of NLEs.

[David Morgan]

well, all of that certainly makes sense. Do wonder however about the validity of it as u mentioned.

[Brian Drysdale]

Originally Posted by David Morgan

well, all of that certainly makes sense. Do wonder however about the validity of it as u mentioned.

In day to day use, the audio reference tone is the part that's most used, rather than the bars themselves, which usually just get a quick glance.

It's a standard procedure which gives the information that might be required further down the line (in broadcast companies or post houses, a number of cameras can be used on a production, with different camera people who aren't around) and forces people not to record on those first 30 seconds (except in emergencies).

In a tapeless workflow this might change, although I can see it still being used to mark card changes and confirm audio settings during transfers. Perhaps you can get away with not doing so if you're just working for yourself, but on large complex productions time can be wasted if you need to run through the rushes to check the sound levels.