Re: dvi vs vga etc and monitors.....
On Tue, May 27, 2008 at 10:17:36PM +0000, Michael Fothergill wrote:
> If you use a vga cable to drive e.g. an LCD TV or a LCD monitor would you expect to get better results i.e. better resolved small font size text using the dvi cable instead?
Using a DVI cable has the advantages:
Image position will be perfect since you a driving the pixels digitally
with no processing of an analog signal required. In fact with a DVI
cable my monitor doesn't even offer image position controls since they
have no meaning anymore.
The VGA connection has no advantages over DVI, other than working with
old hardware.
> Or is that just an old fairy tale?
Converting from digital (video card) to analog (VGA) and then analyzing
the analog signal to try and figure out what the digital information was
(in the LCD) is at best going to match the pure digital connection, but
at worst could get pixel colours slightly distorted (should that red
pixel be 251 or 250 brightness?).
> Is it really true that if you had a very long 50 meter vga cable the signal would degrade and you would lousy graphics resolution in the monitor relative to a short 2 meter vga lead between computer and monitor?
The high frequency analog signal would cause reflections (higher
resolution/refresh rate meant higher signal frequency, often up around
250 to 300MHz per line). Ghosting was common if you used too long a
cable (try working with 5 mouse pointers side by side (getting more and
more faint going to the right with the left most being the real one)
while working with 5 copies of every icon side by side and overlapping).
The digital signal has much better protection against that and is pretty
much a "it works" or "it doesn't work".
> Is it also true that if you switched it for a 50 meter DVI cable then everything would be perfect and the signal degradation would vanish?
Not sure how long a cable it would take before you got bad enough
interference to actually loose the signal on DVI.
> Also if I bought dvi dual link cable and a fancy 2650 x 1600 30 inch monitor could X plus an upmarket nvidia card drive the monitor at its full resolution?
Yes. If the card has a dual link DVI port (not the same as two DVI
ports), then it will drive that at 60Hz. Single link DVI can do up to
1600x1200@60Hz for analog displays (they need timing info embedded) or
1920x1200@60Hz for digital displays (like my 24"). Dual link has two
channels and can do twice that, so 2560x1600@60Hz works great. You can
even do 3840x2400@24Hz or something like that on very high end imaging
displays.
> Apparently you need a dvi dual link cable if you go beyond a certain resolution because neither the vga nor dvi single link can cope with it.
Correct. Dual link cable and dual link capable port on the video card.
THe monitor should come with the cable.
> If it is the case that dvi can't carry sound, can HDMI?
Correct. DVI is video only. HDMI _can_ carry sound, but doesn't have
to. Very few video cards have HDMI yet. For connecting your computer
you will pretty much have to run seperate audio connections for now,
which isn't really that big a deal.
Personally I have not been willing to buy any video card with VGA
connectors on it for the last 3 years. Dual DVI and nothing else. Dual
link would be nice, but wasn't easy to get early on. My 6600GT
surprisingly has both a single and dual link port, which was actually
rare on 6600GT cards. Most were single link on both ports. My 8600GT
of course has dual link on both ports (for some reason 8500 cards almost
always come with a VGA and a DVI which is stupid since the chip supports
dual DVI and the external DVI to VGA adapter is only a few dollars).
--
Len Sorensen
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