Logging of a dv tape – set IN on first frame

[Mark Suszko]

You can, if you do everything manually; set the capture controls for “uncontrolled device”, then cue up the source footage to your first frame by hand, hit the record button in your window and then hit “play” on the deck or camera manually. You should only have to do that for the very first shot on the tape. The dreary saga following tries to explain why.

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When the computer is controlling the deck or camcorder, it has no idea what is on the tape and where. Really,(simplifying a bit here) it only knows that there are control track pulses and time code pulses along the tape at set intervals, like mile markers on a country road, which it counts or reads out, and (simplifying a bit)it can only know those things while the tape is physically moving. It takes a certain number of seconds to get the tape moving up to the proper and stable speed to make reading that information possible in a reliable fashion. We refer to this as “pre-roll”, the bit of tape wasted in getting up to operating speed and in laying down enough control track and time code data so the mechanism of the tape transport can rewind past the right spot, recognize it, decide “ah, I have to stop there, figure out how many seconds to run back behind the desired frame here, in order to be at proper operating speed when that frame crosses the heads again”. Pre-roll is just like the way you back up a couple yards before you try to make a running jump over a big ditch, so you’ll have a running start. Insufficient pre-roll would be like having a wall behind you, keeping you from backing up sufficiently to get that good running start.

So, if there is blank tape before that first frame, the mechanism gets lost, and starts hunting forwards and backwards until it can find it’s way again.

Pre-roll can be long or pretty short, it depends to an extent on the “ballistics” of the tape transport system, i.e. how much inertia the reels of tape carry and how strong the motors are to overcome that inertia. One reason folks like solid state recording is that this issue no longer is relevant when you eliminate a mechanical tape transport.

Over the years I’ve found that the decks I work with most often really like to see at least seven seconds of pre-roll. That is, they like to have clean recorded track for at least seven seconds before the in-point of the edit or the capture. You can sometimes get away with three seconds, but reliability is inconsistent. When I shoot, I like to lay down at least seven seconds of tape rolling before I start the actual shot I will use later. If I crash-record something to a deck, I like to double that to around 15 seconds of clean pre-roll as a “leader” before the program material starts.

You can change the amount of pre-roll specified in your editing system, making it longer or shorter. Longer wastes more of your time and requires more pre-recorded material ahead of the in-point. Make the pre-roll too short, however, and you get poor performance where the machine just isn’t locking up and getting “in the groove” in time to get a good read on the in-point, so it aborts the capture and tries again…and again… and you get stuck in a loop.

This will get you as well when you go to “print to tape”. The deck always looks for tape that has a signal already on it, and will shuttle around until it finds some it can read. Before you try to print to tape with a brand new blank tape, I suggest you lay down about 15 seconds of bars or black on the front of that tape, mark an in-point somewhere near the end of that, and now the mechanisms will all play nice.

[Michael Sacci]

This is why every tape needs to have color bars on the front, his should be done as a force of habit, anything over 30 sec is fine,

[Michael Paul]

You can, if you do everything manually;

Yeh I know. That’s what I’ve meant with capturing it on the fly. Thanks a lot for that big reply. That really explains it.