[sdiy] [AH] analog video synthesizers

[eric b]

>Memory is hazy, but sync should be extractable using a comparitor, right?
>Of course this does nothing for colour, and I imagine that the 8-field
>colour framing system of PAL would screw with any analogue synth's ability to
>do much useful--unless you had a menagerie of digital counters and what not
>going on as well.

Yes, but you also have to preserve the chroma burst, which 
occurs on the vertical sync "pedestal". (unless you don't care 
about totally screwing up the image colors...) A comparator can
separate the pulses, but levels have to be maintained.
Plus, the video signal needs to be clamped. This was done
easily with an 1881 sync separator and CD22402 genlock IC 
plus a 4053 or similar high-speed switch, all preceded
with a clamped video preamp. This is really necessary, believe me.
(esp. if your customer wants to mangle video played back on a typical
low-cost VCR, which can suffer from "flagging" and sync dropouts.)

Unfortunately, the 22402 is not being made anymore and has 
become very scarce. I have not found a similar device, 
even from video specialist IC makers such as Gennum and 
Elantec. This complicates the job. 
The 1881 is also NLA, though Gennum still makes a very 
similar device (GS4882).

>But then again, perhaps video art is considered to be a dead end (an
>expensive one at that) when a decent computer and appropriate software can
do >just as trippy stuff.... but which comes to the problem, there is very
little >decent software out there to do this....

That's the problem--processing audio in real time on a fast PC is
sort-of possible, but video is too much for PCs (as yet). The industry
opinion is that the few professional video engineers who would
want such effects, are willing to use rendering software--and wait
for results. Sometimes a LONG wait.

There are apparently lots of live artists and dance music djs, etc, 
who would like to have a video 'mangler' that can be fiddled with 
in real time. Most of them have never seen the old EMS Spectre or
similar gadgets--those are very scarce today. Even the crude Atari
Video Music is becoming a rare/hot collectible.

>At least we PAL users may hook a modular to a video system...
>Velleman, Belgium have a proc amp kit

I looked at the schematics you linked to--sad to say, 
the Velleman kit uses some Philips video processor chips which
are allegedly no longer available. 
(Please someone tell me I'm wrong!) 

Any 'simple' IC device that can extract and/or 
restore sync and burst is disappearing, supposedly
because it can be used to build low-cost outlaw 
cable-tv decoders....

as I said, the few current commercial cable decoders are now built 
around custom ASICs, or DSP chips and software. 

Worse: the cable TV industry regards analog decoders as obsolete anyway,
they want to force everyone to get digital cable. More profitable,
plus they can force you to look at banner ads when changing channels...

If you want to mess with PAL video, buy the Velleman kit quick!

Or, make it really easy on yourself--get an old RGB analog monitor,
feed it sync from a sync generator, and run your modular synth
signals into the R, G and B inputs. You might need to use a 
camera to capture your results....sorry....this would be a cheap
way to go, for your diyers.





E. Barbour
metasonix