Displayport 1.4 Cable Length

[Excaliburke]

A long time ago, I was looking for the maximum length that my Displayport cable could be to connect a 1440p 144hz monitor to my 980 ti. I discovered that the maximum length is about 15 feet, give or take a couple feet based on the quality of the cable. I tried huge numbers of cables and different solutions and eventually had to move my furniture instead of getting a longer cable. With Displayport 1.4 on newer graphics cards, such as the GTX 1080, are potential cable lengths higher than they were before? Or is a long cable run still in the realm of Thunderbolt?

[mariushm]

The higher the bandwidth the shorter the length OR you encode data in a better format OR you increase the number of wires OR you increase transmission power..

 

Passive cables are limited by specification/standard to 3 meters.

ACTIVE cables can go up to 33 meters... example of such cable : https://www.amazon.com/StarTech-com-DISPL15MA-Active-Displayport-Cable/dp/B00EG3YA2G

 

[Excaliburke]

I know for a fact that that cable is not compatible: I bought it. The "active" cables do not actually work with 1440p 144hz monitors.

[mariushm]

49 minutes ago, Excaliburke said:

I know for a fact that that cable is not compatible: I bought it. The "active" cables do not actually work with 1440p 144hz monitors.

The maximum bandwidth is clearly listed in the specifications:

 

Link : https://www.startech.com/eu/Cables/Audio-Video/DisplayPort/15m-Active-DisplayPort-Cable-M-M~DISPL15MA

 

Quote

The 15m cable offers a bandwidth of 10.8 Gbps with support for maximum resolutions up to WQXGA (2560×1600) and optional audio support. The cable is both HDCP and DPCP capable, which ensures that digitally protected content is displayed properly.

 

From https://en.wikipedia.org/wiki/DisplayPort#Resolution_and_refresh_frequency_limits_for_DisplayPort :

 

Shorthand	Resolution	Frame rate	Data Rate Required[a]	DisplayPort Version / Maximum Data Rate
				1.0–1.1a	1.2–1.2a	1.3	1.4
				8.64 Gbit/s	17.28 Gbit/s	25.92 Gbit/s	25.92 Gbit/s
1080p	1920 × 1080	30 Hz	1.58 Gbit/s	Yes	Yes	Yes	Yes
		60 Hz	3.20 Gbit/s	Yes	Yes	Yes	Yes
		120 Hz	6.59 Gbit/s	Yes	Yes	Yes	Yes
		144 Hz	8.00 Gbit/s	Yes	Yes	Yes	Yes
		240 Hz	14.00 Gbit/s	No	Yes	Yes	Yes
1440p	2560 × 1440	30 Hz	2.78 Gbit/s	Yes	Yes	Yes	Yes
		60 Hz	5.63 Gbit/s	Yes	Yes	Yes	Yes
		75 Hz	7.09 Gbit/s	Yes	Yes	Yes	Yes
		120 Hz	11.59 Gbit/s	No	Yes	Yes	Yes
		144 Hz	14.08 Gbit/s	No	Yes	Yes	Yes
		165 Hz	16.30 Gbit/s	No	Yes	Yes	Yes
		240 Hz	24.62 Gbit/s	No	No	Yes	Yes

 

So of course 2560x1440 at 144 Hz won't work, since the bandwidth required (14 gbps) is higher than the 10.8 gbps the cable supports. The value is listed on both Amazon page and the Startech site, you just have to look.

 

It may go up to 100 Hz or something like that... 120Hz is still too much bandwidth ... at 2560x1440 RGB24 or YCbCr 4:4:4:4 you're looking at around 0.11 gbps per frame ... simple math: 2560 x 1440 x 3 bytes per color x 8 bits in each byte = 88473600 bits * 10/8 (10 bits for every 8bits of data, 2 bits are error correction) = 110,592,000 bits = 0.11059 gbps without any data formatting) .. 10.8 gbps / 0.11059 = ~ 97 Hz

 

The 14.08 gbps at 144 Hz is for RGB24 or YCbCr 4:4:4 ... if you somehow manage to set the output of your video card to YCbCr 4:2:0 (is possible on AMD cards with driver hack/registry tweaks) , you could probably squeeze 2560x1440 120 Hz in 10.8 gbps. You'd notice the color degradation when playing games and maybe in Windows but when watching movies you wouldn't notice anything as videos are already encoded in YCbCr 4:2:0)

 

Anyway, so basically the active cable is slightly above DisplayPort 1.1a but not quite manages DisplayPort 1.2 when it comes to maximum throughout.

 

But let's be serious.. how many people actually have 144 Hz monitors and how many feel the need to have the monitors 15 meters away from the PC? It's a really small niche market, you have to admit.