Why am i loosing my 4th monitor to DSC?

[Teletha]

i have 2 1080p 60hz monitors, and a LG 4K 120hz and the G9 neo at 5120x1440 120hz

When i enable 240Hz on the neo i lose my 4th 1080p monitor, to DSC.

But isn't it still the same bandwidth that is going thru the cable, why does it need to remove the max outputs to only 3 monitors? 

 

[filpo]

Just now, Teletha said:

But isn't it still the same bandwidth that is going thru the cable, why does it need to remove the max outputs to only 3 monitors? 

 

Some gpus can only give a certain amount of bandwidth on all ports at the same time. This is normal since most gpus can't run ALL the ports at the highest bandwidth. It's annoying but its therew

[Teletha]

but with 120hz the bandwidth is still maxing out the cable at 31.85Gbps so if anything the DSC should make it even lower 

DSC is 3:1 compression so the bandwidth of the display at 240 is 63.7 Gbps and compress it with 3:1 will make it 21.23 Gbps

 

unless dsc is on even at 120hz? then it would be only running 10.61Gbps at 120hz

[filpo]

6 minutes ago, Teletha said:

but with 120hz the bandwidth is still maxing out the cable at 31.85Gbps so if anything the DSC should make it even lower 

DSC is 3:1 compression so the bandwidth of the display at 240 is 63.7 Gbps and compress it with 3:1 will make it 21.23 Gbps

 

unless dsc is on even at 120hz? then it would be only running 10.61Gbps at 120hz

its weird. Do you have an igpu you can use?

[Teletha]

oh it seems it uses 2 ports to aggregate the bandwidth when DSC is turned on. Kinda weird if it already compresses it down to 21Gbps

 

 

 

• When a display is connected to the GPU and is set to DSC mode, the GPU may use two internal heads to drive the display when the pixel rate needed to drive the display mode exceeds the GPU’s single head limit. This may affect your display topology when using multiple monitors.  For example if two displays with support for DSC are connected to a single GeForce GPU, all 4 internal heads will be utilized and you will not be able to use a third monitor with the GPU at the same time.
  
  --https://nvidia.custhelp.com/app/answers/detail/a_id/5338/~/using-high-resolution%2Frefresh-rate-displays-with-vesa-display-stream

[Teletha]

4 minutes ago, filpo said:

its weird. Do you have an igpu you can use?

ye but the pc gets random black screen with that on sadly 

[filpo]

1 minute ago, Teletha said:

oh it seems it uses 2 ports to aggregate the bandwidth when DSC is turned on. Kinda weird if it already compresses it down to 21Gbps

 

 

 

• When a display is connected to the GPU and is set to DSC mode, the GPU may use two internal heads to drive the display when the pixel rate needed to drive the display mode exceeds the GPU’s single head limit. This may affect your display topology when using multiple monitors.  For example if two displays with support for DSC are connected to a single GeForce GPU, all 4 internal heads will be utilized and you will not be able to use a third monitor with the GPU at the same time.
  
  --https://nvidia.custhelp.com/app/answers/detail/a_id/5338/~/using-high-resolution%2Frefresh-rate-displays-with-vesa-display-stream

I think you might have to live with the lower refresh rate then or lower the refresh rate/res on the LG 4k 120hz monitor

[Teletha]

6 minutes ago, filpo said:

I think you might have to live with the lower refresh rate then or lower the refresh rate/res on the LG 4k 120hz monitor

i tried lowering everything apart from the 240hz but it wont enable the extra port its hardlocked if dsc is active it seems. 

[filpo]

4 minutes ago, Teletha said:

i tried lowering everything apart from the 240hz but it wont enable the extra port its hardlocked if dsc is active it seems. 

Try turning it off then 

[Glenwing]

27 minutes ago, Teletha said:

oh it seems it uses 2 ports to aggregate the bandwidth when DSC is turned on. Kinda weird if it already compresses it down to 21Gbps

 

 

 

• When a display is connected to the GPU and is set to DSC mode, the GPU may use two internal heads to drive the display when the pixel rate needed to drive the display mode exceeds the GPU’s single head limit. This may affect your display topology when using multiple monitors.  For example if two displays with support for DSC are connected to a single GeForce GPU, all 4 internal heads will be utilized and you will not be able to use a third monitor with the GPU at the same time.
  
  --https://nvidia.custhelp.com/app/answers/detail/a_id/5338/~/using-high-resolution%2Frefresh-rate-displays-with-vesa-display-stream

It's a pixel rate limitation (i.e. before the compression is applied), the final transmission bit rate is not the issue.

[Teletha]

8 minutes ago, Glenwing said:

It's a pixel rate limitation (i.e. before the compression is applied), the final transmission bit rate is not the issue.

Do you think this will have the same issue on DP 2.1 on the 5000 series nvidia gpus too?  Since i will have to upgrade in that case so i can get DP 2.1 without needing to use DSC so i can ultimately have 4 monitors. 

 

since the bandwidth is 63.7Gbps without DSC it has extra 17Gbps headroom but not sure if that applies to the pixel rate too

[Andrewtst]

5 minutes ago, Teletha said:

Do you think this will have the same issue on DP 2.1 on the 5000 series nvidia gpus too?  Since i will have to upgrade in that case so i can get DP 2.1 without needing to use DSC so i can ultimately have 4 monitors. 

You are facing the similar issue as mine, I can only said GPU is the limitation as of now.

 

I lost 3rd monitor when I make my Neo G8 and Neo G9 both running at 240hz.

 

Is it RTX 3080 limitation or Samsung Odyssey monitor issue. Hmm... - Displays - Linus Tech Tips

[Teletha]

2 minutes ago, Andrewtst said:

You are facing the similar issue as mine, I can only said GPU is the limitation as of now.

 

I lost 3rd monitor when I make my Neo G8 and Neo G9 both running at 240hz.

 

Is it RTX 3080 limitation or Samsung Odyssey monitor issue. Hmm... - Displays - Linus Tech Tips

ye that 4k 240hz is at 71.66 Gbps even more that the neo haha. well 2 DSC monitors turns off 2 ports so you only have those 2 that are active. 

Im hoping that the new msi Oled 49" has DP 2.1 so i can replace the neo and wait for the 5000 nvidia gpu for the DP2.1 hopefully it wont need DSC for the pixel rate limit. 

[Andrewtst]

3 minutes ago, Teletha said:

ye that 4k 240hz is at 71.66 Gbps even more that the neo haha. well 2 DSC monitors turns off 2 ports so you only have those 2 that are active. 

Im hoping that the new msi Oled 49" has DP 2.1 so i can replace the neo and wait for the 5000 nvidia gpu for the DP2.1 hopefully it wont need DSC for the pixel rate limit. 

Yup, the only thing now is waiting for RTX 5000 series and hope it came with DP 2.1 and I believe it will since 7900 XTX already came with DP 2.1, and also need change new monitor that is DP 2.1 support as well.

[Teletha]

1 minute ago, Andrewtst said:

Yup, the only thing now is waiting for RTX 5000 series and hope it came with DP 2.1 and I believe it will since 7900 XTX already came with DP 2.1

ye they 100% need to have it. so many high-end monitors coming out now