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Posted by Toby on 03/02/06 15:34
"David McCall" <david.mccall@comcast.net> wrote in message
news:nwnIf.3948$Nj7.2103@trndny09...
>
> <blackburst@aol.com> wrote in message
> news:1139931655.211071.134400@g44g2000cwa.googlegroups.com...
>>
>> Most, if not all, of the 3/4" decks have a "steering sync" or "advance
>> vertical sync" input that does, indeed, steer the servo in that deck,
>> but the input signal for that connector is usually a dedicated output
>> of a TBC. I'm guessing that it would not work as you hope.
>>
>> On the other hand, if you have a deck that takes a blackburst input,
>> that might work.
>>
> All of the 3/4" decks that were designed for linear editing would
> have sync inputs. IIRC the advanced sync is an output from the
> timebase corrector you will be feeding the deck into. This output
> is created by the timebase corrector and will be in sync with
> "house sync" except that it will be a few lines early. That way the
> TBC will have time to buffer the video and get it to the switcher
> at the right time. Without advance sync, the TBC will have to buffer
> the whole frame and put it out a frame late. This is assuming that
> the deck is being fed sync at all. If the deck is free wheeling (no
> sync input), then the TBC will wind up doubling up frames, or
> dropping frames as needed to keep the output in sync.
>
> Prosumer switchers work this way all of the time because there
> is no sync between the deck and the switcher, so the decks are
> always free wheeling. The TBCs in these units are actually frame
> synchronizers. In fact most modern TBCs are frame synchronizers.
> That means that they have a buffer that can hold an entire frame
> and release the video in sync with the "house sync" no matter
> what the source is doing. Frame synchs usually have the capability
> of doing a freeze frame too. Early TBCs did not have this capability.
>
> Advanced sync was essential on early TBCs because the buffers
> were very small. 16 lines was fairly common. The output of a tape
> deck will not be completely stable on it's own. Even if they are locked
> to an external sync, there will be errors involving minor fluctuations
> in speed. A TBC, even with a small buffer can take out these minor
> imperfections in speed as long as they are within the bounds of
> what the TBC can handle. If the errors exceed the buffer, then the
> image will completely fall apart.
>
> David
Thx David--very informative post.
Toby
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