202 lines
4.3 KiB
HTML
202 lines
4.3 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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>Tradeoffs in Configuring your System</TITLE
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>X.org/XFree86 Video Timings HOWTO</TH
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NAME="tradeoffs"
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>8. Tradeoffs in Configuring your System</H1
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><P
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>Another way to look at the formula we derived above is</P
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><PRE
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> DCF = RR * HFL * VFL
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>That is, your dot clock is fixed. You can use those dots per
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second to buy either refresh rate, horizontal resolution, or vertical
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resolution. If one of those increases, one or both of the others must
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decrease.</P
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><P
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>Note, though, that your refresh rate cannot be greater than the maximum
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vertical sync frequency of your monitor. Thus, for any given monitor at a
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given dot clock, there is a minimum product of frame lengths below which you
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can't force it.</P
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><P
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>In choosing your settings, remember: if you set RR too low, you will
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get mugged by screen flicker. Keep it above 60Hz. 72Hz is the VESA
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ergonomic standard. 120Hz is the flicker rate of fluorescent lights
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in the U.S. (100MHz is Europe and other places with 50-cycle current);
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if you're sensitive to those, you need to keep it above that.</P
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><P
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>Flicker is very eye-fatiguing, though human eyes are adaptable
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and peoples' tolerance for it varies widely. If you face your monitor
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at a 90% viewing angle, are using a dark background and a good
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contrasting color for foreground, and stick with low to medium
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intensity, you *may* be comfortable at as little as 45Hz.</P
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><P
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>The acid test is this: open a xterm with pure white back-ground
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and black foreground using <SPAN
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CLASS="application"
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>xterm -bg white -fg
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black</SPAN
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> and make it so large as to cover the entire viewable
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area. Now turn your monitor's intensity to 3/4 of its maximum
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setting, and turn your face away from the monitor. Try peeking at
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your monitor sideways (bringing the more sensitive peripheral-vision
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cells into play). If you don't sense any flicker or if you feel the
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flickering is tolerable, then that refresh rate is fine with you.
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Otherwise you better configure a higher refresh rate, because that
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semi-invisible flicker is going to fatigue your eyes like crazy and
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give you headaches, even if the screen looks OK to normal
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vision.</P
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><P
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>For interlaced modes, the amount of flicker depends on more factors
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such as the current vertical resolution and the actual screen
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contents. So just experiment. You won't want to go much below about
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85Hz half frame rate, though.</P
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><P
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>So let's say you've picked a minimum acceptable refresh rate.
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In choosing your HFL and VFL, you'll have some room for
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maneuver.</P
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>Interpreting the Basic Specifications</TD
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> </TD
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>Memory Requirements</TD
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