Custom Resolution Utility (CRU)

[fandangos]

I would like to post here first to thank ToastyX, every once in a while Custom Resolution Utility saves the day fixing something.

Second I want to post here because I have yet to read about this particular scenario and fix anywhere else online and this might help a few others.

I'm the owner of a LG OLED B9 but the same applies to LG OLED C9.
The B9 and C9 uses two IC for it to be able to support hdmi 2.1. Because of that it supports the full 48 gb/s bandwidth of HDMI 2.1.

This means 4K @ 120Hz RGB Full Range Gsync/Freesync HDR/Dolby Vision at 12 bits.

LG from CX model forward and as far as I know all other tv manufactures that claim hdmi 2.1 support support HDMI 2.1 at a max of 40 gb/s.

This means 4K @ 120Hz RGB Full Range Gsync/Freesync HDR/Dolby Vision at 10 bits.


I bought a 30 meter long Vention fiber optics cable from China that claims 4k@120 hz support but could not get this to work at all from my RTX 3080 TI GPU.
So, to my luck Custom Resolution Utility is still being updated to this day and has hdmi 2.1 EDID management support. It can read the hdmi 2.1 data block.

Those fiber optics cable have an IC that needs to "encode" and "decode" the signal so it can be sent as light trought the cable.
This improves on how far it can be extended but at the same time you need to upgrade the cable so it supports a larger bandwidth.

Knowing all that, what I did here to be able to use this fiber optics cable with my RTX graphics cards is to change under HDMI 2.1 support under the Extension Block, change maximum FRL from 48 gbps (12 x 4 lanes) to 40 gbps (10 x 4 lanes) and it works.
I can enjoy 4k @ 120 hz rgb gsync at 10 bits.

It's not just dropping from 12 bits to 10 bits on Nvidia Control Panel that would have solved this. It needs to change how the image is sent.
I could not get 4k @ 62 hz before, it max out at HDMI 2.0 18 gbps bandwidth. Even with custom resolution and reduced timings 4k @ 61 hz would not work.

So, I'll post this here and in another forum to help whoever else has this problem.

And by the way, this isn't a problem using this cable with Xbox Series S/X or Playstation 5 because those 2 consoles support only up to 40 gbps the same as LG OLED C1 G1 CX and GX.

Once again, thank you ToastyX without CRU I would be screwed.