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Old 19th Jan 2019, 5:36 pm   #3
mhennessy
Dekatron
 
Join Date: Jul 2007
Location: Evesham, Worcestershire, UK.
Posts: 4,238
Default Re: BBC Micro RGB - SCART INPUT VIA VCR

Could you remember any of the model numbers? I'd be keen to understand why they did that. Did they contain a PAL decoder so that they could be used with RGB monitors that lacked their own PAL decoder, or did they generate RGB internally for on-screen graphics or teletext, or did they pass through RGB from other devices connected to them, such as a DVD player?

In the scheme of things, there is relatively little difference between S-video and RGB (or, to put that another way, I remember being pleasantly surprised at how little difference there was!), providing the saturation control is set correctly. There is quite a large difference between composite and S-Video, of course. On a tape that was recorded off-air, the "damage has already been done", so there's no difference between composite and S-video connections between VCR and TV set, assuming the YC filters in the VCR perform the same as the ones in the TV. So what comes off the tape is S-video at best (if it came from an S-video source), and in practice the quality is often no better than composite. So going to the trouble of decoding to RGB won't bring about an improvement in picture quality, assuming the VCR's PAL decoder performs equally to the one in the TV...

Back in the days of only one RGB scart on TV sets, I would have loved a VCR that passed through RGB from the DVD player. I can't remember exactly why now, but there was something not quite ideal about having to go VHS -> S-VHS -> DVD player -> $ky box -> TV set, but that was what I had to do to get RGB from the sources that generated it, while still being able to pick up the audio from the right place to feed to the hi-fi.

Every Sony DVD player I've seen with 2 scarts had a bunch of relays to pass through all the signals - including RGB - when powered down. The $ky box didn't use relays, but was powered all the time, so made do with analogue mux ICs. I seem to recall that there was a slight degradation of picture quality, but not enough to be noticeable from normal viewing distances on a 21" TV.

Anyway, I completely agree about the superiority of RGB, but am keen to learn what those VCR did with it.

Also, given that Macrovision inserted spurious pulses in the blanking period, how does RGB avoid this? All domestic devices that I've seen that output RGB will simultaneously output composite video at the same time, providing a fallback for when you connect to a scart input that is composite only. The sync separator in the device receiving this signal would therefore see no difference. Macrovision is something that occasionally caused us grief back in the '90s, and from what I can remember of those times, I can't quite see how RGB outputs from a VCR would help, unless the machine incorporated a Macrovision cleanup circuit that was disguised as something else - which would be genius marketing if true. Any information you can point me to would be greatly appreciated.

Mods, I realise how off-topic this has become, so might it be worth splitting off these posts into a separate thread?

All the best,

Mark

Last edited by AC/HL; 19th Jan 2019 at 6:07 pm. Reason: Thread split
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