Custom Resolution Utility (CRU)

[mdrejhon]

(05-17-2020 06:33 PM)ToastyX Wrote:  

(05-16-2020 11:51 PM)Reonu Wrote:  Sorry, but I'm a bit of a noob at creating custom resolutions and I don't wanna screw something up. I'm not sure what you mean by "the totals".

By the totals, I mean the totals. I don't know what else to say. Just copy the same timing parameters and see if that works.

Chief Blur Buster here.

I rarely post here, but here's a visual opportunity to help CRU users understand CRU better:

This is correct. Make sure all the number textboxes in "Detailed Resolutions" exactly match each other.

The most important numbers is definitely the numbers in the Totals boxes must match each other, in addition to Refresh Rate. If you do this correctly, the Pixel Clock (number of pixels per second that the GPU generates) becomes identical, and the displays are in sync with each other.

It's possible to have the same Totals with slightly different sync numbers, but if you're unsure, just copy every single number over from one display to the next. You might find it works better if you copy numbers of Display B to Display A, rather than from Display A to Display B.

Both ways will usually work but some displays will be very picky (you'll know when the display glitches or blacks out).

A simplified diagram of the structure of a video signal essentially looks like this:


(Credit: Me. Diagram created by Blur Busters for the Blur Busters website)

-- Mathematically, porches and sync are mapped like a virtual resolution beyond the visible screen resolution.
-- "Total" means the grand total of horizontals (Sync + Porches + Resolution), and the grand total of verticals (Sync + Porches + Resolution).

You want both the Horizontal Total and the Vertical Total to match, in order to get identical Pixel Clock (number of pixels per second generated by GPU) in order for the signal to be in perfect sync.

The art of serializing a 2D picture into a 1D wire, is accomplished via "scanning" -- the raster scan. This means refresh cycles are transmitted one pixel row at a time, top-to-bottom, over the cable. Like the days and weeks of a calender, except 1080p is like a calender 1920 days long by 1080 weeks tall. Pixels are transmitted sequentially like the days of a theoretically enlarged calendar grid. The porches are overscan areas (padding originally used to give some time for CRT electron guns to overscan a curved tube) and the sync areas are signals to indicate the next pixel row (horizontal), or next refresh cycle (vertical). Those were often long enough to allow an electron gun of a CRT to move to its new position.

The 1930s analog TV signal and a 2020s DisplayPort still use the same signalling methods. Today, they're metaphorically more like punctuation marks and comma separators to signal the display to begin a new pixel row refresh, or begin a new refresh cycle. The amazing fact is that the signal structure has remained the same for 100 years. Even as we add things like packetization and DSC (bunching up multiple pixels into bursts). But the signal structure and signal sequencing is fundmanetally unchanged. A few screens will refresh sideways or bottom-to-top, but they are all still raster-based scanout mechanisms.

Once you mentally do that, the numbers in a CRU becomes less scary.

Now, a TestUFO animation that flashes one frame at a time (http://www.testufo.com/scanout) in rapid sequence, then filmed by a 960fps ultra slo-mo smartphone:

[Video: https://www.youtube.com/watch?v=rOyoOm4o82M]

You can see High Speed Videos of Refresh Cycles, of a display refreshing from top-to-bottom. Most low-lag LCD screens will have cable scanout synchronized to panel scanout (sub-refresh latency), just like a CRT but without the flicker. This is very clear in high speed videos when LCD GtG is much faster than a refresh cycle.

Once you have seen a high speed video of http://www.testufo.com/scanout in operation, this diagram below begins to make a lot more sense temporally:



Now, VBI = Vertical Blanking Interval = The total sum of Vertical Front Porch + Vertical Sync + Vertical Back Porch.

The "VSYNC" setting in a graphics driver and video games is a flag that tells the GPU to wait for the Vertical Sync before presenting a new frame. So if you didn't know what the hell a "VSYNC" was, it was named after that "Vertical Sync" signal inside the vertical blanking interval, used to signal the start of a new refresh cycle. It is but one of the several numbers in CRU.

For your purposes, you need Horizontal Total and Vertical Total to be identical to make refreshing on both displays stay in sync (without latency-sawtoothing or beat-frequency stutters of slightly-different Hz). The Windows compositor can only synchronize to one monitor at a time, so synchronizing the Hz is important for consistent latency and stutter-free operation.

Hope this helps some newbies to understand the numbers in ToastyX CRU better!