I want to expand a bit more on HDMI 2.1 vs DP 1.4 as the more research I do and think about the implications, the more necessary I believe HDMI 2.1 is for a $2,500 VR 3.0 device (prepare for another wall of text). With DP 1.4, we’re at risk of having a premium device
- with a bulky set of cables (two display cables, one data cable, and one power cable); or
- less bulky set of cables (one display cable, one data cable, and one power cable) but gimped resolution and refresh rates…
The standard specs are as follows:
- DP 1.4 = 32.4 Gb/s max bandwidth (26 Gb/s usable)
- HDMI 2.1 = 48 Gb/s max bandwidth (42.6 Gb/s usable)
That translates to the following max resolution and refresh rate support:
- DP 1.4 without DSC = 8K@30Hz with 4:2:0 subsampled colors / 4K@60Hz
- DP 1.4 with DSC = 4K@120Hz / 8K@60Hz
- HDMI 2.1 without DSC = 8K@30Hz with full 4:4:4 colors / 4K@144Hz
- HDMI 2.1 with DSC = 4k@240Hz / 8K@120Hz
The Pimax 12K displays should be about 5760x3240 each. That’s 18662400 pixels per eye, for a total of 37324800 pixels for a Pimax 12K headset. Since they advertised HDR support, we can assume a 10bit per pixel color depth. If we calculate that out with a refresh rate of 90Hz, we get a total signal bandwidth output of 120.94 Gb/s. With DSC, we have a 3:1 compression ratio for a visually lossless result of 40.31 Gb/s , which puts us within HDMI 2.1’s usable bandwidth of 42.6 Gb/s.
For comparison, let’s calculate the total signal bandwidth divided by the DSC compression ratio for the Pimax Crystal (using 2880x2880 per panel, 10bit color depth, 120Hz refresh rate). The result is 23.89 Gb/s, which puts us within DP 1.4’s usable bandwidth of 26 Gb/s.
This means that a single DP 1.4 cable with DSC is enough for the Pimax Crystal. At the same time, the Pimax 12K will require two DP 1.4 cables with DSC to achieve its full resolution per eye at 90Hz (base numbers, not accounting for any other proprietary tech they use on top of DSC).
That being said, they may use the Tobii eye tracking along with NVIDIA VRSS 2.0 for foveated transport to push the refresh rate at the Pimax 12K’s max resolution per eye from 90Hz to 120Hz. This is nice for us with NVIDIA graphics cards (if implemented with a focus on high res and refresh rates…), but that doesn’t mean they shouldn’t implement support for AMD Radeon 7000 cards at 90Hz.
On the other hand, they may use foveated transport to try and barely squeeze the bandwidth on just one DP 1.4 cable to avoid the bulkiness and inconvenience of two DP 1.4 cables. In an interview with MRTV, the COO briefly mentioned that there are two prototypes: one with one DP 1.4 cable and another with two DP 1.4 cables. While neither situation is ideal, using one DP 1.4 cable is even worse than using two DP 1.4 cables. If they use only one cable, then foveated transport would be required to just barely achieve 90Hz at full resolution. Higher refresh rates will come at the cost of heavily reducing resolution (and FOV).
I think it’s a massive mistake not to go with a single HDMI 2.1 cable. They should take the time to do two very important things: add AMD Radeon 7000 GPU support and use HDMI 2.1 instead of DP 1.4.
P.S. Some other features of HDMI 2.1 that will improve the Pimax 12K even further if implemented:
- HDMI Cable Power - Enables active HDMI cables to be powered directly from the HDMI connector without attaching a separate power cable. This would potentially future-proof the Pimax 12K to ditch the power supply and only two required cables (HDMI and USB) on supported graphics cards.
- Variable Refresh Rate (VRR)
- Quick Frame Transport (QFT)
- Quick Media Switching (QMS)