[Bob Zelin] “when you do a dub from one SDI VTR to another, you are sending a digital signal from one VTR to the other – this is commonly called “making a clone” – because you are transfering the digital data.”
Bob, I used to think this was the case, but I was shocked to learn that it’s not. Check out this link:
https://www.kenstone.net/fcp_homepage/beyond_dv_nattress.html
Graeme Nattress certainly knows what he’s talking about. Here’s the relevant excerpt:
“Clone Dubbing
Some video recorders, such as Digital Betacam do not give the outside world access to the uncompressed data on the tape, so cannot be edited natively. This also means that you cannot do a perfect clone dub of a Digital Betacam tape.
The compressed output, which we use to edit a video format natively, can also allow a perfect clone of a digital tape to be made. You can easily make a perfect (within the bounds of dropout and data related errors which might, theoretically, over many repeated such dubs reduce the picture quality) dub by connecting a firewire cable from one DV deck to another, pressing play on the first and record on the second. Some DVCAM decks will also copy the timecode from the original over to the new copy too.
When tape-to-tape dubbing via an uncompressed SDI output you cannot make a clone copy. This is because the video must be uncompressed on the play-out machine, and then re-compressed on the recorder, which will theoretically reduce the picture quality (perhaps only slightly in the case of formats like Digital Betacam) and not be a perfect clone. In practice, dubbing from Digital Betacam to Digital Betacam over SDI is visually lossless over hundreds of generations, and indeed, the error correction used in Digital Betacam is so good that tapes with errors on them can often be improved through a Digital Betacam to Digital Betacam over SDI dub.”