Converting TTL monitor to Analog

From: Richard Erlacher <edick_at_idcomm.com>
Date: Thu May 10 13:14:17 2001

Well, you may be onto something, but it was widely accepted back in the '70's
that a human couldn't see the flicker in an interlaced TV picture, and they
certainly wouldn't see flicker in 60 Hz refresh of a text/graphic display. In a
subdued light environment, not toally dark, but somewhat subdued, particularly
in the absence of flourescent lighting, I can't see the normal 30 Hz interlace
in normal network TV broadcast signal at all. I can, however, ALWAYS, see the
interlace in those overlays produced on AMIGA video editing tools (probably the
cheap ones, but often used at educational institutions' video production
studios.) I'm aware of this only because a friend of mine told me what was used
to produce them, and sometimes their credits include details about how the text
and graphics were integrated into the video.

I'd suggest you try looking at the 60+ Hz monitor that gives you a headache in
an environment free from flourescent lighting. You might even try watching it
in a subdued-light, but not dark environment, with something pleasant on the
screen. I can look at code or schematic diagrams for about 8 -10 hours, after
which it gives me a headache. I'm just trying to rule out effects other than
the "flicker" that nobody could see back in the '70's. Back then the 30 Hz
interlace was what occasionally caused folks to complain. Maybe I've just been
"hardened" to that effect by much exposure.

The "beat" between the nearly-60 Hz at which many monitors do their vertical
retrace, and the considerably-closer-to-60 Hz at which the lights flash can
certainly cause ill effects.

Maybe there's an advantage to being unable to see this purported flicker.

Dick

----- Original Message -----
From: "Roger Merchberger" <zmerch_at_30below.com>
To: <classiccmp_at_classiccmp.org>
Sent: Thursday, May 10, 2001 9:58 AM
Subject: Re: Converting TTL monitor to Analog


> Rumor has it that Richard Erlacher may have mentioned these words:
> >Hogwash!
>
> Hogwash, yourself. Altho I usually agree with what you type, I must
> seriously disagree with you here...
>
> >56Hz won't produce any flicker a human can detect. It may beat with the
> local
> >lighting, but it won't flicker noticeably.
>
> I can *easily* see 56 & 60Hz flicker, and anything below 72Hz can give me a
> headache. (Interlaced VGA can give me a *monster* headache in under 30
> minutes.) 75Hz for me is borderline but usable, and 85Hz & above are my
> "target zones".
>
> (also, the larger the tube, the easier it is to see the flicker -- at least
> for me - I'm running 75Hz at work on a 19" tube, and I can still see it.)
>
> Just because *you* cannot see the flicker, doesn't mean all humans cannot
> see or be affected by the flicker.
>
> Anywho, just thought I'd throw my $0.000002 in...
>
> Roger "Merch" Merchberger
> --
> Roger "Merch" Merchberger --- sysadmin, Iceberg Computers
> Recycling is good, right??? Ok, so I'll recycle an old .sig.
>
> If at first you don't succeed, nuclear warhead
> disarmament should *not* be your first career choice.
>
>
Received on Thu May 10 2001 - 13:14:17 BST