Date   : Tue, 15 Mar 2005 23:35:32 +0000 (GMT)
From   : Ian K <BBCmail@...>
Subject: Re: Beebem question / game copyright question

In article <1110922538.12696.163.camel@...>,
   Jules Richardson <julesrichardsonuk@...> wrote:
> On Tue, 2005-03-15 at 20:14 +0000, Tim Fardell wrote:
> > Jules Richardson wrote:
> >  > For various reasons (screen sync being the main one) it'll be
> >  > rigged, with a machine behind the scenes running XP and driving an
> >  > old monitor.
> > 
> > Hang on - call me stupid if you like, but I would have thought that
> > screen sync would be *much* more of a problem with a PC monitor, than
> > a genuine BBC (or any old home computer for that matter) outputting a
> > standard 50Hz scan rate! As long as the camera is using a 1/50
> > shutter speed it should work fine. Yes, they could set the PC monitor
> > to 100Hz, which would work, but why make it more difficult than it
> > needs to be? What am I missing here??

> Don't ask me :) I'm just going on what they've said to me, and I assume
> their tech guys know what they're doing. 

> I suppose they have gadgets that'll *guarantee* there are no flicker
> problems, but they probably only have a VGA plug at one end and a socket
> at the other. Probably such gadgets are only designed to work at a
> modern range of video frequencies though, so even of someone wired up
> the right cable, it still wouldn't work.

The only way to guarantee no flicker is to make sure the frame rate is the
same and that each scan is triggered on the monitor and the camera at the
same time. This is either achieved by having all equipment timed from the
same sync signal or using a genlock adapter which will delay one signal so
it is in time with another. 
As you suggest they likely want to use the PC because they know it is
going to work within modern tolerances and wont cause any complications
although the BBC should generate ideal signals.
Ironically the BBC used BBC's to generate captions and video effects for
many years. They even produced a broadcast standard genlock interface for
it so they could used in this way to display things on monitors and
generate captions.

Regards
Ian K