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Main Event: DV Demons...and How to Exorcise Them
Posted Nov 2, 2004 - April 1998 [Volume 7,Iissue 5] Issue Print Version     Page 1of 2 next »

Back in the days of analog, event shooters struggled along with S-VHS and Hi8 because most of us couldn't afford Betacam SP or MII gear. We complained about dropouts—those white horizontal streaks caused by particles of oxide falling off the tape, taking a bit of the picture signal with them—and generation loss, the blurring and bleeding of the picture that occurred each time the image was copied during the editing process.

Enter DV. No more dropouts, no more generation loss. DV had crisper, more colorful images, arguably equivalent to Betacam SP. Best of all, the equipment was affordable.

The Six Demons
But for all DV's advantages, the format has some demons of its own, waiting to corrupt our precious footage. Here are some of those demons and how to deal with them.

Head Clogs: DV uses a tape only 1/8" wide. The drum spins at 9,000rpm, scrubbing your heads across the tape at a great rate. It's easy to clog the tiny recording heads with material scrubbed off the tape. Worse, different manufacturers use different tape lubricant formulas. When mixed in your camcorder, they can interact to form a sticky gunk that quickly clogs your heads, and even jam your transport mechanism. Worst of all, your camcorder may or may not detect a head clog. You might not find out about it until you replay the tape back at the studio.

Digital Dropout: DV is highly resistant to dropout because the same data is recorded multiple times within the track. The playback electronics compare the multiple data streams, and reject those that are corrupted by an oxide particle dropping off the tape. The dropouts are still there, but you don't see them on the screen. But if the dropout is big enough, the correction circuits don't have enough data to work with, causing digital dropout, which results in a sudden blockiness in the picture. The worse the dropout, the larger the blocks, until the picture is lost completely. They are much rarer than analog dropouts, but they're much more noticeable when they do happen. 

Digital Artifacts: NTSC DV's 4:1:1 color space can cause a "stairstep" effect, especially on sharp diagonal edges in the image. In addition, getting a clean chromakey can be difficult with this format. 

Playback Incompatibility: Tiny differences in transport alignment can cause a tape recorded in Camcorder A to exhibit video or audio dropout, or become unplayable, in Deck B. The likelihood of this increases if you record using the LP mode. Using equipment from different manufacturers also increases the chance of incompatibilities, but in rare cases it can even happen when moving tapes between two devices of identical make and model.  

Fragile Equipment: DV isn't fragile per se; ruggedized cameras are available. Unfortunately, lower-priced "prosumer" camcorders are often made to consumer standards, and don't hold up well to the stresses of professional use. The on-off cycles, the frequency of use, and the amount of handling are all at a higher level than the designers envisioned, leading to a fairly high failure rate.

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