Jump to content
To encourage social distancing, you must leave two blank lines at the start and end of every post, and before and after every quote. Failure to comply may result in non-essential parts of the forum closing. Click for more details. ×
Search In
  • More options...
Find results that contain...
Find results in...
Glenwing

Guide to Display Cables / Adapters (v2)

Recommended Posts

On 1/27/2017 at 7:38 AM, Glenwing said:
 

 
Bandwidth / Maximum Refresh Frequency Calculator [Link]
 

 
Note: Actual video transmission does require blanking intervals. The "Timing Format: None" option should only be used for mathematical curiosity, not to determine how much bandwidth a video signal actually needs. Even though modern non-CRT displays do not actually need blanking intervals to physically operate, these intervals have been repurposed in interfaces like HDMI for transmitting auxiliary data such as inline audio and control signals, and therefore are still required for the operation of display devices.
Close

Can a monitor use the extra bandwidth to achieve a higher refresh rate if it doesn't send an audio signal through a DP 1.4 port? Or is it always limited to 25.92GBPS no matter what?


CPU Intel Core i9 9900K @ 5.1GHz Motherboard Asus Maximus XI Hero RAM 16GB KFA2 HOF @ 4GHz CL17 GPU Gigabyte GTX 1080 Ti Case Caselabs Mercury S8 Storage Samsung 950 Pro 256GB, Samsung 840 Pro 256GB, Seagate SSHD 1TB, Intel 530 180GB PSU Seasonic Focus+ Platinum 850w Display LG 38GL950G Cooling Custom WC Operating System Windows 10 Pro x64

Link to post
Share on other sites
Posted · Original PosterOP
14 minutes ago, Jonny93 said:

Can a monitor use the extra bandwidth to achieve a higher refresh rate if it doesn't send an audio signal through a DP 1.4 port? Or is it always limited to 25.92GBPS no matter what?

Audio is included in the 25.92 Gbit/s, and it takes up a pretty small amount anyway (≈1.5 Mbit/s normally)

Link to post
Share on other sites

Will the new HDMI 2.1 standard require new hardware or can I expect that the TV from 2019 will get software updates and will be able to use this standard with the right cable?

Is it even possible to update version 2.0 to 2.1 using software because I read on several pages related to Samsung that their QLEDs from 2019 will get such functionality through soft.

I need to buy a new TV now and the choice fell on the Samsung Q60R 55".

Link to post
Share on other sites

Correct me if I'm wrong, but in order to get Gb/s, shouldn't bits per second be divided by 1073741824 (aka 1024 / 1024 / 1024), not 1000000000 (aka 1000 / 1000 / 1000)?

 

For instance: 3840x2160 120Hz 8bpc RGB (None) (None) gives a value of 23.89Gb/s, but shouldn't it be 22.25Gb/s? That's a whole 1.64Gb/s difference! Possibly enough to matter when choosing a standard!

 

Is there an exception for some reason when calculating uncompressed video data rates, like there there seems to be when calculating hard drive space?

Link to post
Share on other sites
Posted · Original PosterOP
16 hours ago, Qb_Master said:

Correct me if I'm wrong, but in order to get Gb/s, shouldn't bits per second be divided by 1073741824 (aka 1024 / 1024 / 1024), not 1000000000 (aka 1000 / 1000 / 1000)?

No, 1 Gbit/s = 1,000,000,000 bit/s. This is the definition used by the entire industry since forever :)

Quote

Is there an exception for some reason when calculating uncompressed video data rates, like there there seems to be when calculating hard drive space?

It's not a special exception, it's the industry standard ;) Data transmission rates conventionally use decimal prefixes, and most other things do as well.  They aren't, and have never been, specified with the binary definition. This applies to all data transmission, not just display interfaces. Gigabit ethernet for example is 1,000,000,000 bits per second, not 1,073,741,824 bit/s. SATA's 600 MB/s, JEDEC's RAM designations (like PC4 25600, meaning 25,600 MB/s), graphics card memory bandwidth, video bitrates for compressed video files, audio bit rates (160 kbit/s = 160,000 bit/s) etc. all uses the decimal definitions. Decimal prefixes are used pretty much across the industry, it's not "just the hard drive manufacturers" as some people seem to believe. It's actually the binary definition which is fairly niche, it's really only used for integrated circuit-based memory cell capacity, like RAM or CPU cache, nothing else.

 

When it comes to display interfaces, HDMI 2.0 for example signals at 6.0 GHz on each signal pair. That's decimal, because GHz is an official SI unit and therefore 6.0 GHz is unambiguously defined as 6,000,000,000 Hz. HDMI carries one bit per signal, and therefore the bitrate of the interface is 6,000,000,000 bits per second, per channel. With all 3 channels aggregated, that's 18,000,000,000 bit/s. So HDMI 2.0's "18 Gbit/s" is using the decimal definition. Transmission rates are always based on a signaling frequency which is a nice round decimal number, and therefore always come out as a round decimal bit rate. Hence decimal prefixes are more suitable. They're far easier to calculate that way, and there is no inherent advantage or logical reason to using binary multiples in this field.

Link to post
Share on other sites

I'm sorry but I'm a bit confused by your graph. I am currently saving up for the Asus PG27UQ (4K 144Hz HDR 1000 monitor). I would like to use the 10-bit, YUV444 HDR settings for the best color and HDR ratio. That monitor apparently only has HDMI 2.0 and Displayport 1.4. Does this mean I have to scale my FPS down to 120Hz or to 98Hz?

 

Thanks!

Link to post
Share on other sites
Posted · Original PosterOP
49 minutes ago, Emiel255 said:

I'm sorry but I'm a bit confused by your graph. I am currently saving up for the Asus PG27UQ (4K 144Hz HDR 1000 monitor). I would like to use the 10-bit, YUV444 HDR settings for the best color and HDR ratio. That monitor apparently only has HDMI 2.0 and Displayport 1.4. Does this mean I have to scale my FPS down to 120Hz or to 98Hz?

 

Thanks!

https://www.anandtech.com/show/13060/asus-pg27uq-gsync-hdr-review/3

 

Quote

All told, DisplayPort 1.4 was designed with just enough bandwidth to support 3840x2160 at 120Hz with 8bpc color, coming in at 25.81Gbps of 25.92Gbps of bandwidth. Notably, this isn’t enough bandwidth for any higher refresh rates, particularly not 144MHz. Meanwhile when using HDR paired with the P3 color space, where you’ll almost certainly want 10bpc color, there’s only enough bandwidth to drive it at 98Hz.

 

Link to post
Share on other sites

DP 1.4 provides around 25.92 Gbit/s of bandwidth. Multiple sources say that LG 38GL950G works in {3840x1600, 24 bit/px, YCbCr 4:4:4, no compression, 160 Hz} mode, that requires around 26.01 Gbit/s of bandwidth with CVT-R2, according to the calculator.

 

Any thoughts?

Link to post
Share on other sites
Posted · Original PosterOP
6 hours ago, tarsius said:

DP 1.4 provides around 25.92 Gbit/s of bandwidth. Multiple sources say that LG 38GL950G works in {3840x1600, 24 bit/px, YCbCr 4:4:4, no compression, 160 Hz} mode, that requires around 26.01 Gbit/s of bandwidth with CVT-R2, according to the calculator.

 

Any thoughts?

Probably uses non-standard timings to get slightly lower rates. They don't have to use standardized formulas like CVT-R2.

Link to post
Share on other sites
Posted · Original PosterOP
2 hours ago, r0otctrl said:

Anybody know how I can go about testing my new "Ultra Speed" cable to verify that it's not an inferior spec ???

 

Thanks

The actual test equipment is thousands of dollars, so not really :P But if the manufacturer got theirs certified, they should have the certificate from an Authorized Testing Center to prove it, you can try asking them for it.

Link to post
Share on other sites
Just now, Glenwing said:

The actual test equipment is thousands of dollars, so not really :P But if the manufacturer got theirs certified, they should have the certificate from an Authorized Testing Center to prove it, you can try asking them for it.

I will do that. Thanks

Link to post
Share on other sites
3 minutes ago, Glenwing said:

The actual test equipment is thousands of dollars, so not really :P But if the manufacturer got theirs certified, they should have the certificate from an Authorized Testing Center to prove it, you can try asking them for it.

The thing that bothers me is that it showed up with "High Speed" printed on the cable itself. I asked them about it and they said it was done to reduce manufacturing costs, which seems super fishy to me...

Link to post
Share on other sites

Hello,
I am facing some issue regarding my recent upgrade. Can somebody help me.
Previous Setup:
GPU: EVGA 980ti
Monitor: Asus VG248QE
Connectivy: DVI-D both end
 
New Setup:
GPU: EVGA RTX 2080
Monitor: Asus VG248QE
Connectivy: DVI-D using included DVI-D to HDMI adapter. DVI-D at monitor end. DVI-D to HDMI adapter then to HDMI port since 2080 doesn't have any DVI port.

Will upgrading to DP-DP cable solve the issue or is there anything i can do to fix it. TIA for responding.

Link to post
Share on other sites
Posted · Original PosterOP
3 hours ago, rvxspeed said:

Hello,
I am facing some issue regarding my recent upgrade. Can somebody help me.
Previous Setup:
GPU: EVGA 980ti
Monitor: Asus VG248QE
Connectivy: DVI-D both end
 
New Setup:
GPU: EVGA RTX 2080
Monitor: Asus VG248QE
Connectivy: DVI-D using included DVI-D to HDMI adapter. DVI-D at monitor end. DVI-D to HDMI adapter then to HDMI port since 2080 doesn't have any DVI port.

Will upgrading to DP-DP cable solve the issue or is there anything i can do to fix it. TIA for responding.

Yes, use a DP cable.

Link to post
Share on other sites

Thunderbolt 2 supports dual DisplayPort 1.2, so shouldn't the max bandwidth be 20 Gbps instead of 17.28 Gbps, like you did for Titan Ridge with dual DisplayPort 1.4? You already have a DisplayPort 1.2 option so there isn't much reason to keep Thunderbolt 2 the same (unless the extra 2.72 Gbps cannot be used).

 

With Titan Ridge, the extra 5.44 Gbps allows the Apple Pro Display XDR to run at 6K 60Hz 10bpc RGB using a dual link SST DisplayPort 1.4 HBR3 connections without DSC. Computers that support DSC (macOS/Windows: 5300M, 5500M, W5700X, maybe 5700XT?; Windows: RTX) use a single link SST DisplayPort 1.4 HBR2 connection with DSC at up to 12 bpc (though the display is 10 bpc).

 

I admit that with Thunderbolt 2, there's not much you can do with an extra 2.72 Gbps. A 5K dual link SST display could increase refresh from 46Hz to 53Hz (CVT-RB 8bpc RGB). But first you would need to find a display that can support such a timing (I think the LG UltraFine 5K and Dell UP2715K only support 60Hz?) and an OS that will allow that timing twice on a single Thunderbolt 2 connection.

 

In macOS, if you connect a 4K display then there is no bandwidth remaining for another display. To connect two 4K60 displays to Thunderbolt 2, you first have to connect a low bandwidth display (such as a 1440p display or a DisplayPort to VGA adapter or HDMI 1.4 adapter). With the 1440p display, some bandwidth remains to connect a second display. Connect the first 4K display. Then disconnect the 1440p display. The bandwidth reserved for the 1440p display is freed so it can be used by another display (it is not reassigned to the already connected 4K display). Finally, connect the second 4K display.

 

I can only get the two 4K displays to work at 1440p73 over Thunderbolt 2. This is not sufficient to prove that more than 17.28 Gbps can be used. Maybe it's a limitation of the macOS driver. Lowering the refresh of one display does not allow the refresh of the second display to be increased because the bandwidth is assigned when the displays are connected.

 

Maybe behavior in Windows is different for Thunderbolt 2 connected displays.

 

Link to post
Share on other sites
Posted · Original PosterOP
1 minute ago, joevt said:

Thunderbolt 2 supports dual DisplayPort 1.2, so shouldn't the max bandwidth be 20 Gbps instead of 17.28 Gbps, like you did for Titan Ridge with dual DisplayPort 1.4? You already have a DisplayPort 1.2 option so there isn't much reason to keep Thunderbolt 2 the same (unless the extra 2.72 Gbps cannot be used).

The extra can't be used. The same applies to the Titan Ridge actually, which is a mistake I need to fix. Titan ridge allows either four or eight lanes of HBR2 (17.28 Gbit/s or 34.56 Gbit/s) or four lanes of HBR3 (25.92 Gbit/s), it can't operate in an eight-lane HBR3 mode with a 40 Gbit/s cap.

Link to post
Share on other sites
On 1/12/2020 at 1:56 AM, Glenwing said:

The extra can't be used. The same applies to the Titan Ridge actually, which is a mistake I need to fix. Titan ridge allows either four or eight lanes of HBR2 (17.28 Gbit/s or 34.56 Gbit/s) or four lanes of HBR3 (25.92 Gbit/s), it can't operate in an eight-lane HBR3 mode with a 40 Gbit/s cap.

I don't think there's anything to fix with Titan Ridge. Somehow Apple makes it work to support 6K with GPU's that don't support DSC (read my post linked below). The capability required a firmware update for the Blackmagic eGPU's Thunderbolt controller (but I need an AGDCDiagnose output to verify that dual HBR3 is working from the BlackMagic eGPU and Macs - I only have info for dual HBR2 and HBR2 DSC modes).

 

My test with two HBR3 displays with a GC-TITAN RIDGE shows one display can connect at HBR3 speed and the other can connect at HBR speed, which is the same bandwidth as dual HBR2 (34.56 Gbit/s).

 

With Thunderbolt 2, I explained how to connect two HBR2 connections. Thunderbolt does not transmit DisplayPort stuffing symbols which reduces the actual amount of DisplayPort data transmitted. This allows the remaining bandwidth to be used by PCIe packets. Stuffing symbols are recreated when a Thunderbolt controller converts the Thunderbolt DisplayPort packets back to DisplayPort.

 

I think with USB4 you're going to see more complicated chains (and trees!) with more than two DisplayPort endpoints where this bandwidth issue will need to be addressed or it will just get worse. This wasn't a problem with MST, because the OS (not macOS) knows the MST topology and can know exactly how much bandwidth is available taking into consideration the bandwidth currently being used by connected displays based on their timing and pixel format. Maybe the OS needs to treat Thunderbolt more like MST if that's possible. Otherwise, the only way to fix this is for the OS to allow the user to select how much to reserve for the next connected display (if the OS is able to convey this info to the Thunderbolt controller with the free DisplayPort input).

 

 

Link to post
Share on other sites
Posted · Original PosterOP
2 hours ago, joevt said:

I don't think there's anything to fix with Titan Ridge. Somehow Apple makes it work to support 6K with GPU's that don't support DSC (read my post linked below). The capability required a firmware update for the Blackmagic eGPU's Thunderbolt controller (but I need an AGDCDiagnose output to verify that dual HBR3 is working from the BlackMagic eGPU and Macs - I only have info for dual HBR2 and HBR2 DSC modes).

 

My test with two HBR3 displays with a GC-TITAN RIDGE shows one display can connect at HBR3 speed and the other can connect at HBR speed, which is the same bandwidth as dual HBR2 (34.56 Gbit/s).

 

With Thunderbolt 2, I explained how to connect two HBR2 connections. Thunderbolt does not transmit DisplayPort stuffing symbols which reduces the actual amount of DisplayPort data transmitted. This allows the remaining bandwidth to be used by PCIe packets. Stuffing symbols are recreated when a Thunderbolt controller converts the Thunderbolt DisplayPort packets back to DisplayPort.

 

I think with USB4 you're going to see more complicated chains (and trees!) with more than two DisplayPort endpoints where this bandwidth issue will need to be addressed or it will just get worse. This wasn't a problem with MST, because the OS (not macOS) knows the MST topology and can know exactly how much bandwidth is available taking into consideration the bandwidth currently being used by connected displays based on their timing and pixel format. Maybe the OS needs to treat Thunderbolt more like MST if that's possible. Otherwise, the only way to fix this is for the OS to allow the user to select how much to reserve for the next connected display (if the OS is able to convey this info to the Thunderbolt controller with the free DisplayPort input).

 

 

Thank you. My information comes from here:

https://thunderbolttechnology.net/sites/default/files/18-241_Thunder7000Controller_Brief_FIN_HI.pdf

 

I will have to look into this further.

Link to post
Share on other sites
10 hours ago, Glenwing said:

My information comes from here:

https://thunderbolttechnology.net/sites/default/files/18-241_Thunder7000Controller_Brief_FIN_HI.pdf

 

I will have to look into this further.

Us mere mortals don't get access to the real Thunderbolt documentation. The USB4 spec is publicly available and may describe most of how Thunderbolt works. Section 10 is all about DisplayPort tunnelling. Section 10.4.2.1 is about Path Configuration: Setup. The next page (pg 362) describes how the Connection Manager calculates bandwidth available to limit the maximal link rate and lane count of the DP IN adapter's DP_REMOTE_CAP register. I guess Apple changed this calculation to allow two HBR3 four lane connections. I need an AGDCDiagnose output to prove that (but I believe there's no other way to get 6K without DSC). I wonder if two HBR3 connections is allowed only for the XDR display, or if it will also work with my two displays (It's actually one Acer XV273K with two DisplayPort 1.4 inputs). If it does work with the Acer to allow two HBR3 connections, I wonder what happens if I increase the refresh rates so that the bandwidth exceeds the 40 Gbps limit (does it gracefully disconnect, stop, or show garbage). I don't have a Titan Ridge Mac with AMD dGPU to test.

 

A correction to what I said previously about connecting two 4K displays to Thunderbolt 2 (method: connect HBR display first, then first 4K, then replace HBR display with second 4K). The AGDCDiagnose outputs show that they both connect with DisplayPort 1.1 HBR four lanes. To get one to be connected with DisplayPort 1.2 HBR2 four lanes, they both need to be disconnected first. This behavior matches what is described by the USB4 spec (I'm not sure why the DisplayPort version needs to change - just the link width and lane count should be sufficient).

 

The limit calculation described by USB4 has a problem. If I have 4 lanes of HBR available, will it allow 2 lanes of HBR2? I did this test with a two lane DisplayPort 1.2 adapter after setting up a single HBR x4 connection to Thunderbolt 2. The answer is that it connects with 2 lanes of HBR instead of HBR2. This is not optimal. Apple is right to allow max link rate and lanes (exceeding 40 Gbps) instead of that silly calculation.

 

The problem (that Apple bypasses for the XDR?) is that a limit is placed on both lanes and link rate, but bandwidth is the product of both, where HBR x4 is the same as HBR2 x2. Another but: for Thunderbolt, bandwidth is about pixels per second and not related to DisplayPort lanes and link rate (stuffing symbols are removed - see Figure 10-22 in the USB4 spec). 6K doesn't require full dual HBR3 but does require more than dual HBR2 so Thunderbolt 3 Titan Ridge should be able to handle 6K as Apple has made it do. Ideally, a user should be able to lower the bandwidth used by a display (decrease refresh rate or resolution or pixel depth) to increase the bandwidth allowed for another display connected to the same Thunderbolt 3 port without disconnecting/reconnecting the displays.

 

Another situation where the limit calculation has a problem: If I have a Thunderbolt 3 dock with an internal DisplayPort 1.4 MST hub (like the HP Thunderbolt Dock G2) connected to a Thunderbolt 2 port, then any display (even if it is HBR only) connected to the hub will use the full DisplayPort 1.2 HBR2 four lane connection of the hub so a second display cannot be connected to the Thunderbolt port of the HP Thunderbolt Dock G2. Of course, an MST hub allows multiple displays to be connected, but that doesn't work in macOS which doesn't support MST for multiple displays (but does support MST for old 4K displays that use a separate stream for each side of the display).

 

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


×