[SOLVED] Understanding docking stations, resolution, and refresh rates

[Ryan990]

I am trying to understand resolution and refresh rates if I use a USB C docking station on my new gaming laptop.

First note is the laptop does not have thunderbolt, its just pure USB C.

I am looking for a usb c docking station that'll support 2 video outputs. One over DP or HDMI for my 1440p gaming monitor and one over HDMI for my 4k TV. My question is if it says it can do duel displays at 60Hz, is that 60Hz per display or total (30Hz each)? If its 60Hz each can that be increased if the other display is off, if for example I want a higher refresh rate going to my gaming monitor?

 

[vov4ik_il]

I want a higher refresh rate going to my gaming monitor?

If the dock only uses USB-C it has a built in display adapter (gpu) which will 100% lack performance for gaming but will do just fine for office applications. You should use external GPU or the laptop display port (if the laptop GPU is sufficient) for gaming. Refresh rate limits are usually the monitor limitations today, whereas FPS rates are actual performance capabilities of the graphics card in an application.

 

[Ryan990]

An external gpu would be overkill as the laptop already has a RTX 2060 in it. It doesn't have DP out but it does have HDMI which I suspect would be sufficent.

What doesn't make sense about that though is I read elsewhere that a usb c to display port dongle can handle upto 240Hz @ 1440. I don't understand why the dock would be any different.

If you have a video-capable USB Type‑C port, you can use a USB‑C to DisplayPort adapter. This is equivalent to a native DisplayPort connection. Current devices support up to DisplayPort 1.2, so up to 240 Hz at 1080p or 165 Hz at 1440p. USB‑C adapters also work in Thunderbolt 3 ports.

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These adapters will only work if the USB‑C port has video output capability. Not all USB‑C ports have this capability, it is an optional feature.​

 

[vov4ik_il]

Those dongles use USB-C port in DP mode. They do not provide you with additional devices.

 

[Ryan990]

Those dongles use USB-C port in DP mode. They do not provide you with additional devices.

Isn't that how to docks work too just with adding in other usb functions though? Because I know they won't work on a system that does not support DP over USB-C....

 

[vov4ik_il]

Isn't that how to docks work too just with adding in other usb functions though? Because I know they won't work on a system that does not support DP over USB-C....

Docks usually use USB-C as a USB hub and have other devices attached to it. Adapters use the whole interface as DP in alt mode.
Edit: At least this is how I understand reading the spec.

 

[Ryan990]

I spoke with a technical rep at a manufacturer of these docking stations. I still don't get how but he said they can do a signle 4k display at 120Hz over usb c with nothing else, just a dongle because that requires the full bandwidth usb-c has to offer. But somehoe they have some way to offer 2 4k displays simultaneously at 60Hz in a docking station.

It would seem to me 2 4k @ 60Hz would use the same bandwidth as 1 4k @ 120Hz So I really don;t understand how they can do one but not the other with all the other peripherals in a docking station. But that seems to be a current limitation of the technology.

So then it seems I have to decide I can do HDMI out to my TV, a usb-c to displayport adapter to my 1440p gaming monitor to get the high refresh rates and a regular USB type A to a hub for all my USB peripherals, and my power plug for a total of 4 cables. Or I can do power adpater and usb c dock for only two cables but be limited to maybe a little better than 60Hz on the 1440p display since thats a lower resolution than 4k and 60Hz to my TV?

So much for the clean astethic of a usb c dock to minimize cables to my laptop I guess...

 

[vov4ik_il]

hey can do a signle 4k display at 120Hz over usb c with nothing else, just a dongle because that requires the full bandwidth usb-c has to offer

That's what I understand from the spec too. It uses DP mode rather than USB and all the USB functions are unavailable. Now in the dock that has two ports they use a USB GPU which is low performance.