🚀 go-pugleaf

In article <2196@ecs.soton.ac.uk> mrd@ecs.soton.ac.uk (Mark Dobie) writes:
>We are trying to connect our VCR output to the video input of the
>Philips 410 and then use the RGB and sync output from the 410 to drive
>a monitor. Essentially we want to use the 410 to convert the VCR video
>signal to RGB plus sync signals.
>
>We get the RGB signals and the sync, but the sync is unstable.
>Can anybody help us?

Ok - I think the answer to this question is fairly straight forward.
The syncs from the video disc players CVBS to RGB convertor is unstable
because the output of the VCR is unstable.  Video disc players are at
present unique among domestic/industrial video equipment in that they
store the full-bandwidth video signal without modification or recoding.
This means that the signal is recorded syncs, monochrome picture and
colour burst all as one chunk.

Due to this method of recording, the raw output from the laser pickup
and FM decoder contains the colour sub-carrier as its highest frequency
component.  The naturally unstable timebase of any replay system affects
the sub-carrier particularly badly - VCRs get round the problem by
recoding the colour burst to a lower frequency, minimising the instability.
Video Disc Players can't, and so they always have a built-in timebase
corrector to sort out the problems.  It's important to note that the
video disc internal timebase correctors are simpler than the free
standing devices for video cassette recorder usage in that they do
not attempt to correct for drop-outs to the same extent.

Anyway, the bottom line is that the output from a video disc player
will have a rock steady timebase and the CVBS -> RGB decoder will
rely on those syncs being stable, merely stripping them off and
using them.  A VCR without a time base corrector will be all over
the place!  (Just try comparing the pictures of a video disc player
and a VCR on a monitor with cross-pulse - uggggh!)

So the moral of this story is:

	a) get a time base corrector for the VCR
	b) get a CVBS -> RGB decoder that cleans up the syncs while
	   its about it.

Hope this helps.

Regards, Bevis


Bevis King, Systems Programmer        |   Email:  brwk@doc.ic.ac.uk
Dept of Computing, Imperial College   |   UUCP :  brwk@icdoc.UUCP
180 Queens Gate, London, SW7 2BZ, UK. |   Voice:  +44 1 589 5111 x 5085
          "Never argue with a computer" ... Avon (Blake's 7)