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Dynamic refresh rate: why not?

XTF

Gawd
Joined
Oct 11, 2011
Messages
591
Just wondering, why do LCDs not support dynamic refresh rates? Videocard renders frame and transmits it to the monitor as soon as it's ready, waiting just doesn't seem to make sense.
 
Just wondering, why do LCDs not support dynamic refresh rates? Videocard renders frame and transmits it to the monitor as soon as it's ready, waiting just doesn't seem to make sense.

Because video transmission standards require a timing signal that supplies information about the refresh rate. Every time it changes the monitor needs to re-sync. You can do it in a few frames but not instantaneously.
 
Those standards are not law of nature, they can be changed and improved.
 
there is no "dynamic refresh rate" because LCD panels actually get very similar timings and require them to operate. Frames must be changed constantly and with equal timings. It wouldn't have any sense to implement variable refresh rate and then still convert it to static refresh rate internally just to drive panel. And ofcourse there would still be maximum frequency...

Besides, only games would benefit from such thing and here 120Hz is enough to deal with v-sync
 
there is no "dynamic refresh rate" because LCD panels actually get very similar timings and require them to operate. Frames must be changed constantly and with equal timings.

Are the technical details of this explained somewhere?
And how do some of those Korean displays get around this? Some appears to be able to support any frequency between 60 and 120 Hz.
 
Are the technical details of this explained somewhere?
And how do some of those Korean displays get around this? Some appears to be able to support any frequency between 60 and 120 Hz.

All displays transmit an EDID (extended display information data) to the video card to tell them what the recommended timings are, but most video drivers can be programmed to ignore the EDID and provide their own timings.

LCDs don't actually need strict timing formulas and can usually operate at a range of refresh rates. Usually that range is very limited (like 59-64 Hz) but not always. For example, the Dell 2209WA is popular on this forum because it go up to 75Hz. The Korean monitors can be "overclocked" to up to 125 Hz if given the right signal and the right hardware is used, and many laptops can "underclock" their LCDs from 60Hz to 50Hz to save battery power.

For technical details of how TMDS (the standard in DVI, HDMI, and DisplayPort) works, see section 3 of this doc: http://www.ddwg.org/lib/dvi_10.pdf
 
XTF;[URL="http://cliobeta.cul.columbia.edu:7018/vwebv/search?searchArg=1038946239&searchCode=ISNS&limitTo=none&recCount=25&searchType=1&page.search.search.button=Search" said:
1038946239[/URL]]Thanks, but that's the non-interesting part. It's 'just' the link between video source and panel and doesn't dictate the requirement for a fixed refresh rate.

After reading closely, I think you might be right, according to 3.3.2 (page 30): "The receiver is required to establish synchronization with the data streams during any blanking period greater than 128 characters in length."

But if it messes up in any way, then you lose at least a frame ("lost synchronization").
And even after the TMDS receiver syncs, the monitor has to turn that into an output. I don't know how the internal electronics of the monitors sync to any newly-synced input. It may be possible to implement; I don't know.
 
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