Need help understanding DisplayPort -> "HDMI 2.1" adapter issues (stuck at HDMI 2.0b limits, Sabrent DA-UCH8)

Hardware GPU
1

Hi,

I needed an USB-C-to-HDMI adapter for an iPad Pro 2021 and while I’d ideally have one that fully supports HDMI 2.1 I get that there is currently no chipset available that could do this.

But I was under the impression that everything excluding VRR should be possible…

…which doesn’t work in my case.

While the iPad hasn’t been shipped yet I tried two different computer hardware configurations, both have the exact same display output limitations with the Sabrent USB-C-to-HDMI adapter:

  • Full Range RGB with 8 bpc color only works up to UHD/60 Hz
  • Full Range RGB with 10 bpc color only works up to UHD/30 Hz
  • UHD with 61 Hz to 120 Hz only works with 8 bpc YCbCr 4:2:0 :frowning:

(I’d like to get UHD/120 Hz/10 bpc color/HDR/Full Range RGB)

Tested hardware configurations:

  1. 3090, two of its DisplayPort outs go to a Gigabyte GC-Titan Ridge Revision 2.0 AIC that supports DisplayPort 1.4, this Thunderbolt 3 AIC then supplies an USB-C video output for the adapter to use;

  2. 4750G on an ASUS ProArt B550-CREATOR with an onboard Thunderbolt 4 controller that has USB-C video output;

  • LG CX with a 48 Gbit/s-capable HDMI cable, works fine with all features if I directly plug it into an HDMI 2.1 port of the 3090 instead of the Sabrent adapter, the TV has the latest firmware 03.23.06 installed

  • Sabrent DA-UCH8 “USB Type-C to HDMI 2.1 Adapter | 8K/60Hz & 4K/120Hz with DSC Function”

What am I missing?

2

https://www.club-3d.com/en/detail/2535/usb_gen2_type_c_to_hdmi_4k120hz_hdr10_with_dsc_1.2_active_adapter_m-f/

Maybe, I would email them to see if it would work.

3

The internal chipset is likely the same (and I’m pissed at Club 3D for their buggy CAC-1085 adapter that behaves exactly the same regarding the stated limitations (but instable operation) and with a direct DisplayPort input instead of USB-C).

I guess I was kind of hoping Sabrent would have put more care into their adapter’s firmware compared to Club 3D.

4

the Club 3d is Active adapter

This line from the Sabrent makes me think its a passive
"Requires a USB-C port which supports “DisplayPort Alternate Mode” (not all USB-C ports/systems support Alternate Mode functionality). "

1 Like
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That’s only to let people know that not EVERY USB-C port has DisplayPort out capabilities.

Most USB-C ports that are on motherboards without Thunderbolt don’t support DisplayPort out since how should they get a GPU signal if it’s just a separate USB controller…?

Note that both systems I’ve tried aren’t “just” USB-C but the latest Thunderbolt 3 Titan Ridge revision and the current Thunderbolt 4 standard.

6

I would imagine that those adapters should work in any port if they are active. I mean I have USB display hooked up to my X570 board. But maybe its more complex then that, never dug deep into it.

7

That’s a different cup of tea:

The adapters I’m talking about here are the active ones that need a DisplayPort signal from your GPU to work at all (= transcoding DisplayPort signal to HDMI) and the visual performance should be the same as if you plug something directly into your proper GPU.

On the other hand these “2D USB graphics/display adapters” (never had one personally) are basically tiny dGPUs that you connect to the USB bus with all compromises that come with that.
(no fun with UHD or stuff like 120 Hz)

(Note: I’m editing around a bit to make the situation more clear)

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