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Tell HN: Most DisplayPort cables aren't sold with correct information
159 points by bloopernova on Aug 28, 2022 | hide | past | favorite | 52 comments
In every DisplayPort (DP) cable I've seen on Amazon and many other retailers, the main difference between cables is shown as the version of the DP specification that they support.

Unfortunately, that's not what makes a DP cable different from its peers. Every DP cable supports every version of the spec! 1.1 to 1.4, they all support the same DP spec. The difference is in the bandwidth they support: RBR, HBR, HBR2, HBR3, and UHBR 10 (and above). This then translates to the resolution and refresh rate that the cable can support.

The differences are listed here: https://en.wikipedia.org/wiki/DisplayPort#Cable_bandwidth_an...

    RBR (Reduced Bit Rate)            6.48 Gbit/s
    HBR (High Bit Rate)               10.80 Gbit/s
    HBR2 (High Bit Rate 2)            21.60 Gbit/s
    HBR3 (High Bit Rate 3)            32.40 Gbit/s
    UHBR 10 (Ultra High Bit Rate 10)  40.00 Gbit/s
The Wikipedia page also has tables that show what those bandwidths are capable of with regards to resolution+refresh rate: https://en.wikipedia.org/wiki/DisplayPort#Refresh_frequency_...

If you want 4K @ 60Hz you need a HBR2 cable. For 4K @ 144Hz you need UHBR 10.

Some retailers are better at telling you what bandwidth their cables support, such as Startech which does list the BR: https://www.startech.com/en-us/search?search_term=HBR3

Monoprice doesn't show any search results for HBR3: https://www.monoprice.com/search/index?keyword=HBR3&didyoume...

Cable Matters does have some results, but doesn't show the bitrate in the product title: https://www.cablematters.com/search.aspx?PageSize=20&PageNum...

Amazon shows results for HBR3 but so many customer reviews tell of counterfeit cables and straight up lying in descriptions.

If you know of any better retailers that sell UHBR 10 or above cables, please let me know in the comments! I hope this information is useful to someone and saves you some time and pain trying different cables.




LTT got a TotalPhase cable tester and ran tests on a whole bunch of video cables. Lots of cables from major suppliers like Monoprice failed their tests. Here’s the video for DisplayPort:

https://www.youtube.com/watch?v=Vn2vdQZhs0w


Thanks for this link. The results spreadsheet has “UHBR10 passed” in the Notes column for those that did:

https://docs.google.com/spreadsheets/d/e/2PACX-1vQ1maB_K91Aw...


This is why I’m curious to see how LTT will be able to properly monetize their new review unit, for most ppl it’s not interesting to see HOW the widgets were reviewed, they just want to see the results. If the results exist in any form other than the video most people who don’t have time for a video will just skip to going to the webpage that contains the results. And in the case of a gdocs page there’s no ad revenue to monetize those people… so this kinda creates a situation that calls for either gatekeeping like consumer reports or forcing everyone to watch a video and not creating these nice lists which is semi anti-consumer.


They've already stated it's going to have a pretty robust website with good search engine to filter through their test results and blog posts. Then they'll take certain tests and make videos on top of that for the main channel, otherwise they'll be pretty independent business units.


Got it, so it’ll be very different. Monetization will likely be affiliate links and ads, though I wonder if they’ll give float plane subscribers an ad free experience.

Also curious if they’ll be able to keep the firewall between marketing and review that it appears wirecutter has failed to do.


That's been his stance, a lot of the information and planning for the "Lab" have been exposed via their live Friday shows (WAN Show). They just got their power supply testing stuff, too. Linus seems to be really hedging on doing this right, and I'm cautiously optimistic.


Regardless, bless that man.


He gets some flack because his style looks like common, over the top, yt clickbait. But despite the occasional antics there’s a lot of substance behind his content. Other yt celebs are buying Lamborghinis and paying for stupid stunts. Linus just bought a $100k PSU tester.


No way he’d be as successful and be able to do things like this without it sadly. He definitely plays into it as well which I find funny. The community at first was a hit harsh on him for it but they know that’s how they’re able to afford everything.

Those thumbnails and clickbait titles definitely work.


I’m just worried “doing this right” for us means a poor return on investment for him which means it won’t survive very long.


We'll see, he's got his money invested in a lot of different areas, so I'm sure he'll be fine if this venture doesn't work for him. One thing I've noticed is that what he does largely is just based on what _he_ wants. The backpack he had built because he _wanted_ it, the screwdriver was designed because he _wanted_ it. The Lab is being built up because he wants an obscene amount of random testing just done for everything. It certainly seems to drive him, and it's a better motivator than doing something just because "he needs to for more money", ya know?


Surprised that all the Amazon top 10 cables passed UHBR10.


I think amazon does a lot of steering/ranking in their product search results based on things like return rates and reviews, so it's not too surprising that products that work well become popular.


This is simultaneously surprising and not surprising.


Apologies for the links not working in the post. Here's every link:

https://en.wikipedia.org/wiki/DisplayPort#Cable_bandwidth_an...

https://en.wikipedia.org/wiki/DisplayPort#Refresh_frequency_...

https://www.startech.com/en-us/search?search_term=HBR3

https://www.monoprice.com/search/index?keyword=HBR3&didyoume...

https://www.cablematters.com/search.aspx?PageSize=20&PageNum...


A few tech youtubers have noted the problem before with cables and a lack of specifications and many cables not meeting the specs they do list. Amazon is flooded with knock offs with brands that last a month at this point, you will get your money back if it doesn't work as specified but its frustrating that it continues.

I think the problem is even wider than displayport/HDMI cables. It extends to hubs and everything USB as well, the bulk of stuff is sold with very little information compared to the actual specs, most hubs are USB 3.0, a type C connector wont say what parts of the standards it accepts etc etc. Its become an increasing problem on laptops as well, you have USB C ports that may or may not pass displayport and its really unclear at what speed they can do that with the manufacturers refusing to list the specs or even answer the questions.

The specifications have never been more complex and convoluted and it really makes it look like the standards process has been corrupted to be able to sell substandard equipment. This only hurts their brand and customers however who find it hard to get what they want. I would say it starts in the specifications but honestly while convoluted with too many optional parts its the sales end that refuses to accurately portray what their products can do. Its a giant mess at the moment and I don't see any signs its going to get anything but worse.


Yeah agreed on the USB spec. I have a CaberQU USB-C cable tester via Kickstarter, which I can use to see what pins are connected and from there at least guess what they support.

Unfortunately the CaberQU site is down right now, but the Kickstart page is still up: https://www.kickstarter.com/projects/electr/c2c-caberqu-usb-...

I'd love to see something similar for DisplayPort, HDMI and more.


Yeah these cables are definitely a minefield…

The solution is to look for an officially certified cable, they will work as advertised. Displayport.org has a database of certified products.

I already ran into this in 2016 when I got my 4K display. I looked up a certified cable and bought it off Amazon. Worked perfectly as expected.

Same applies to HDMI at more demanding bandwidths.


I got two certified HDMI cables at Walmart (and cross referenced the certification online). One of them worked fine, while the other one worked in a basic sense but failed to negotiate and wouldn't give me all the fancy sound and video options going from my Shield to my LG TV. The other cable, nominally identical, worked fine swapping between them so the other one must have been bad and I ended up returning it for another one that worked.

So even the certified cables can be defective it seems, and more confusing is that they still mostly work. The defective cable would still negotiate 4K and show a nice image, but wouldn't work with stuff like Dolby Vision (and a couple other more advanced modes but that is the one I remember). I probably would have just assumed something else was wrong with my setup and written it off if I hadn't bought an identical cable to swap. I bet a lot of people wouldn't even notice the missing functionality, which is likely how this has become so widespread.


> Monoprice doesn't show any search results for HBR3:

You can (at least partially) chalk this up to a bad search engine. Individual listings (e.g. https://www.monoprice.com/product?p_id=37920) appear to specify supported transmission rates. Here's an excerpt from that page:

  • Supports High Bit Rate 3 (HBR3)
  • Delivers up to 32.4 Gbps data bandwidth
  • Supports Display Stream Compression 1.2 (DSC) visually lossless compression


Same problem with USB-C cables. It’s really hard to find out if it can only charge your phone, or if you can also connect a screen with it (DP).


The easiest way to guarantee these things is to get thunderbolt 3 or 4 cables if you want to have anything beyond basic USB 2 or 3 features. They generally have a lightning bolt on the plug casing.


I know. But they are very short. I think an usb 3 cable can be up to 2 meters. Thunderbolt just 0.8 or something.


if you only need 20gbps (so basically, you're not trying to run a bunch of 4k monitors over one cable) you can get passive 2m tb3 cables that, if certified, are probably higher quality than rando usbc cables, and I don't think that those would be likely to be more capable. Eg: https://www.amazon.com/Certified-Plugable-Thunderbolt-20Gbps...

If you want higher bandwidth and longer you can get active cables or optical ones, but those are obviously more expensive (it's better to think of them as their own electronic device than a cable).


But that implies overpaying for a cable.


If you're literally only using it to carry DP? I suppose. If you're actually using it as a docking cable and you're expecting it to carry usb, video, and power then I think you might have really unreasonable expectations of what it takes to carry all that in one cable and how cheap that's ever likely to be.


I never said it has to be cheap. I said you are over paying because you might be paying for features that you don't use.


I don't think that's really accurate. A passive low bandwidth tb3 cable is basically just a usb3 cable with a defined set of capabilities and a certification. OP wanted power and video, that's what a tb3 cable provides.


My wife tried to charge our Switch Pro Controller with a random usb-c cable only to find out the next day it hadn't charged at all. So frustrating.


Cable Matters, to its credit, does have some discussion of the higher bitrate cables and their availability towards the end of this year: https://www.cablematters.com/Blog/DisplayPort/displayport-2-...


When it comes to buying commodity type electronics, cable matters and anker are just about the only two brands I'll trust/buy unless it's something extremely generic like RCA cables or a 3.5mm headphone adapter


Coolblue has a result https://www.coolblue.nl/en/share-product/834931?utm_medium=i...

Megekko instead has a lot of results https://www.megekko.nl/?r=cdromland

But is a shop focused on pc components so it’s less generic


What happens if a cables doesn't have enough bandwidth for a resolution/refresh rate combo?


The source and the sink negotiate a link rate that allows error free communication, based on the number of errors seen on a known pattern over a certain amount of time during the link training phase.

When the established link rate is too low for a requested video timing, the source requests a less demanding video rate.

It’s why the control panel of a GPU might now show the video timing that your monitor officially supports.

In modern GPUs and monitors, an alternative is that DSC (display stream compression) is used, and that the compression ratio is cranked up to still fit the requested timing in a reduced availabile bandwidth. The image quality impact is usually unnoticeable.


Normal DP cables in particular are entirely passive, there is no chip or coding in them that would tell source/sink what kind of cable it is. IME the most likely result of a marginal cable will be that the screen sometimes goes black for 1-2 seconds or shows an artifact here or there. With DVI, which just directly blasted red/green/blue bits on separate wires at the pixel clock (bad for EMI) it was pretty easy to end up with a cable that had issues just on the twisted pair for a particular color.


Yes, I know they are entirely passive.

That’s why the source and sink need to determine the maximum rate literally based on trial and error.

The source tries a link speed (and other parameters such as drive strength and pre-emphasis), the sink reports back home many symbol errors it detected. Rinse repeat until a stable configuration is found.

For marginal connections that’s often not sufficient. After the introduction of DSC, DP has mandatory support for Reed-Solomon forward error correction, which is a great help in fixing occasional error burst. It can be enabled when DSC is off, but I don’t know that happens in practice.


Wasn't trying to correct you, just adding

Just remembered where I saw your name before - I've been using your timings calculator for years!


Usually the reported maximum res/rate is lower.


I've had good experience with Accell cables so far, they're usually well rated and have proper certification. They do sell HBR3 cables, but nothing more than an announcement for UHBR cables.

EDIT: Club3D is also one of the rare brands selling VESA-certified cables


Personally with DP cables, especially if you're looking for a longer length cable or wanting to push a higher bit rate through it, then you're better off just spending a bit extra and getting a proper VESA certified cable.


Along with that, I've found that fiber based cables tend to be more reliable than the copper ones. I suspect this is because the media conversion causes there to be a cleaner signal at the output since it has to completely recreate it rather than just amplifying it. Leading to better clocking and less rounding of the edges from capacitance of the cable.


Does this apply to DisplayPort KVM switches too? I would think so? I have a DP KVM switch that won't let me run my monitors at their highest resolution, this probably explains it.


Most of the cables I've purchased always list the max resolution, so if a cable says 4k@60hz I would assume it's HBR2


VESA has a list of certified and tested cables (limited #) but if you can go for those ones, it's worth it!


Suggestions on a good USB C to DP for 4k+ @ 144hz?

I have a 49" ultrawide and super hard to get MacBook to work properly.


Sorry, I only just saw this! Cable Matters:

https://www.cablematters.com/pc-1278-154-vesa-certified-disp...

plus this adapter:

https://www.cablematters.com/pc-1038-122-usb-c-to-displaypor...

I'm using these 2 items to get 4K @ 120Hz on my Acer screen, from my intel macbook.


Thank you! No need to apologize, you don't have any obligations lol


I have several DP cables, using it with no problems on 2560x1080. How to figure up which standard they are?


2560x1080 has very low bandwidth requirements. At 60Hz even RBR works! Your cable would have to be almost completely broken for it not to work.

My video timings calculator shows exactly what kind of minimum protocol you need for a given video timing.

https://tomverbeure.github.io/video_timings_calculator


Oh wow, that's really useful, thank you!


Look at this table: https://en.wikipedia.org/wiki/DisplayPort#Refresh_frequency_...

Depending on the refresh rate, your cables are probably HBR.


Pretty much any cable will work at that resolution.

Problems usually happen at 4K resolutions, UWD resolutions (e.g. 3440x1440 and over) and especially at refresh rates over 60Hz.




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