Color bars at beginning of tape?
 

Just wondering, how long (if at all) do you put color bars at the beginning of new tapes when shooting? I was taught to do this when recording SVHS, as the first minute of the tape was unreliable. I still do it with DV, but I'm wondering if I'm cheating myself out of one last glorious minute of possible tape.

You may be cheating yourself; without having done a statistical analysis of any sort to verify, my experiences tell me dropout may occur in the middle of a MiniDV tape as frequently as it will the beginning. Has anyone done a more thorough study?

Tape manufactures suggest that more dropouts will occur at the beginning and ends of tapes because of the manufacturing process (cutting, splicing, attaching to reels etc.) The inner portion of the tape is wound at a much smaller angle, stressing the tape more than the outer portion. The outer portion is more exposed to the elements and possible contamination from environmental causes (dust, lint etc.).

Most dropouts experienced in the old days of 3/4" happened at the beginning and end of tapes; same with Betacam, though never as bad. I haven't seen a dropout in 2 years of DVCAM tapes, but I always put a minute of bars at the head and at least that much rundown at the tail. Tape is the cheapest thing of any shoot--why push the limits? Anyway, you need space at the head of the tape. Professional decks require some preroll, and it's a real pain to try to capture footage from the very beginning of a tape; you can't get it all. Also, if the time code shifts and you expect the very beginning of a shot on down in the tape to be used, that's a pain too. It's easy to be professional when you shoot and have rundown at the head and tail of each shot. If you're just doing home movies, then it's not a problem and don't worry about it.

This is for professional applications. Thanks guys.

Color bars at the front of the tape are primarily intended for monitor calibration. I believe the standard length is sixty seconds. Normally there's a 60khz tone with 'em on the audio track. Bill Pryor would know much more about this than I do, however.

When I used to prepare tapes for broadcast, this is how it was done.

Timecode starts at 23:58:30;00

15 seconds of black

60 seconds of bars and tone

10 seconds of slate and countdown

5 seconds of black

program starts at exactely 00:00:00;00

That way the timecode was also the total run time (TRT).

Some stations wanted the 5 seconds of black so it could be worked into their cart machines or edited etc.

Some stations wanted the timecode to start at

01:00:00;00

so we would just bump everything up 1 hour.

The bars and tone in the beginning of the tape is for either moniotor calibration, as Chris stated, or in post to detemine colour values and audio levels. I work as an editor and I always check the bars in the beginning to make sure they are set to legal values. Every camera/tape vary - if ever so slightly - and balansing them out before capturing saves hours of colour correcting.

So I would say the bars are vital as a reference point and should always be recorded if you want to be able to take you footage anywhere.


I hope this helps.

Regards
Jon

Yep, bars and tone are for calibration, and it helps to have 60 seconds because sometimes you may need that much to get things tweaked properly. But the rundown also serves to not use the head and tail of the tape, where dropouts seem to occur more often. So even if you're shooting for your own use, it's a good idea. As Jon said, the editor checks every tape (or should), because every camera can vary a bit.

Chris it can't be 60 KHz audio unless dogs are doing the sound ;-)

That should be 1KHz 0dB for the tone.

It used to be 1khz 0db, but since the switch to digital where audio cuts out at 0db, it should be set to -20db in the NTSC world and -18 for PAL users, but I believe this has been discussed in another thread if anyone is interested.


Jon

Good comment, but I'm not sure of the answer. I think it depends on what format your working with. Most stations in the states still prefer Beta SP for broadcast and even though the source is digital the edited master is analog and get tone at 0dB. I've sent mini DV tapes out recently to a station with 0dB tone also and nothing was said. I think I'll check a couple of sources and see if I can get a consensus for NTSC.

Don't know where I got 60khz... my Rottweiler can hear that, I guess... thanks for setting me straight!

;-)

Digital audio has different levels
 

-12db digital = 0db analog. If you look at the XL1s audio meters, the 12 is in a solid block. That block is the visual reference for what we know as 0db in the analog world. I didn't realize this at until I returned home after my 1st shoots with some very hot audio. If you play "B & T" in FCP, the tone plays at -12. If you lay off bars and tone to the camera from FCP, the tone registers at -12.


Bill