hdmi 2.1 optical cable latency

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scrdcow
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hdmi 2.1 optical cable latency

Post by scrdcow »

EDIT: I did buy a cable in the end. Hope it's good. Will test in in the future once I have a Time Sleuth. Still interested to hear others views so I leave the post hanging. But if mods want to delete it, feel free.

I plan on getting a 7-8m hdmi 2.1 optical cable for future proofing my setup, instead of getting 2.0. I try to find any real test on latency, but it's hard to find.

I see Bob tested this BIFALE cable a year ago, but it's very expensive and their 2.1 cables are also extremely expensive compared to many others. He also mentioned some cables could add latency.
https://www.retrorgb.com/fiber-optic-hd ... ested.html

I don't have a Time Sleuth or any other good way to test cables and resend them.
The cable also needs to actually be able to perfom what it says, which I will be unable to test today. I guess a certification will make sure of that?

In the end it will be running from a HDMI switch (haven't decided which one yet) to my projector (Benq TH685) which is 2.0. I will not buy a new projector in many years, but hopefully I find a great 2.1 switch that seems trustworthy, so I can future proof that aswell.

Do you guys have any recommendations? Is it even worth future proofing the cable at this point? Am I missing some important aspect?
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NewSchoolBoxer
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Re: hdmi 2.1 optical cable latency

Post by NewSchoolBoxer »

tl;dr It doesn't matter what officially branded HDMI cable you use or what length it is unless we're talking over 25 feet, in which case you might need a Cat5E repeater. The length limit isn't due to latency but rather the voltage dropping enough that the high logic voltage level is interpreted as low logic voltage.
scrdcow wrote: I see Bob tested this BIFALE cable a year ago, but it's very expensive and their 2.1 cables are also extremely expensive compared to many others. He also mentioned some cables could add latency.
https://www.retrorgb.com/fiber-optic-hd ... ested.html
<mod edit - removed inflammatory suggestion>

Some cable makers will disclose the velocity factor, meaning what fraction of the speed of light the signal travels at. Every cable I've seen, this is 0.6 to 0.8. Speed of light is 300,000 meters / 100,000 feet in 1 millisecond. Traveling 60% of that rate, you're not going to have a cable run long enough to notice the latency. HDMI cables must meet official HDMI specs to be sold with HDMI branding. It doesn't matter which of those cables you use. No one tests because there is no need to. This hustle is like new generation of expensive Monster HDMI cables. I hate how I'm defending the HDMI cartel that charges $5000 a year licensing fee to use their plug shape but here we are.

I said no one but I remembered a video labeled "HDMI Input LAG - Fact or Fiction" and spoiler alert: it's fiction.
Watch the first 4 minutes of this video by Shmup Junkie - an actual video system professional not trying to sell you anything - and be amazed: https://www.youtube.com/watch?v=Jx1kiSEaMMM

Starting with 6 ft cable, adding on a Crestron 8x8 matrix and 25 foot cable gives the exact same latency measurement. He then measures the latency on:
100 foot HDMI cable -> 1st Crestron matrix -> 50 foot shielded Cat5E (aka Ethernet) cable -> 2nd Crestron matrix -> 25 foot HDMI cable -> Television

No added latency. He does plug RetroRGB in the video description for great technical overviews.

I could see a switcher or matrix adding on perceptible latency when you switch inputs. I was reviewing relay datasheets and the switching speed ranges from low nanoseconds to a few milliseconds. You might see a switcher or matrix datasheet disclose the propagation delay. That's what you care about. I spent a minute online searching for it and all figures were 2.5 nanoseconds or less.
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bobrocks95
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Re: hdmi 2.1 optical cable latency

Post by bobrocks95 »

Lag will not be a cable problem, though you could end up with a long enough run where you need an HDMI repeater to get a stable signal. But never lag.

For HDMI 2.1 though I paid a premium for an actual certified 48Gbps cable. I kept trying cables that absolutely couldn't do 4K @ 120Hz in HDR (32.27 Gbit/s according to Wikipedia) or even SDR (25.82 Gbit/s) like I needed it to. I ended up buying this cable, but options were limited for cords over 6ft when I bought it: https://www.amazon.com/dp/B08P5PPWRB. I see that Anker still tops out at 6ft for example.

Look for "Ultra High Speed" certified and the shield logo with a QR code in the corner of the packaging, you scan that with an app if you want to ensure your cable is legit. Maybe it's not worth worrying about if you're not using actual HDMI 2.1 level bandwidths, but if you weren't probably any cord would work fine and there's nothing you really need to worry about.

For that cable that retrorgb covers I REALLY don't like that a $180 cable doesn't have a real HDMI certification. Nowhere on that page will you find the words "Certified" or anything containing "Ultra". They carefully dodge those to save a couple dollars, plus I see reviews on there saying they couldn't get it to work with an RTX 3000 series GPU at anything above 4K/60...... If I were paying that much for a cable it'd better work with everything.
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scrdcow
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Re: hdmi 2.1 optical cable latency

Post by scrdcow »

NewSchoolBoxer wrote:tl;dr It doesn't matter what officially branded HDMI cable you use or what length it is unless we're talking over 25 feet, in which case you might need a Cat5E repeater. The length limit isn't due to latency but rather the voltage dropping enough that the high logic voltage level is interpreted as low logic voltage.
bobrocks95 wrote:For that cable that retrorgb covers I REALLY don't like that a $180 cable doesn't have a real HDMI certification. Nowhere on that page will you find the words "Certified" or anything containing "Ultra". They carefully dodge those to save a couple dollars, plus I see reviews on there saying they couldn't get it to work with an RTX 3000 series GPU at anything above 4K/60...... If I were paying that much for a cable it'd better work with everything.
Thanks for your detailed answers.
I could have been a little bit more specific thou.

What I was wondering is if the translation to optical and back will add any lag, and I had a hard time finding any certain answerns online. I knew that cable lenght doesn't matter. I also "needed" optical because it needs to be atleast 8m long running against a wall. So a repeater wouldn't be the prettiest option. I could have gone with cat5e somehow but then I wonder about added lag from the hardware that does the transation as well. I was also very sure to buy a certified cable so as to know it will work with everything in the hdmi 2.1 spec. Especially handle 4k 120hz for the soon to come future without needing to redo the setup.

So it's more these conversions and the hardware used for those that I wonder if any lag will be added. And in this case only for opitcal since I pretty much ruled out most other options (except looking into running cat5 with some smaller gadgets and not a huge matrix-switch or something of thath matter).

Sifting through amazon it seems that it was hard to find a certified cable that wasn't a bit on the expensive side, compared. But I rather get it right the first time and pay a bit more than all the hassle dealing with if it's wrong. So I ended up with this 10m cable -> https://www.amazon.com/dp/B096W788MW
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orange808
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Re: hdmi 2.1 optical cable latency

Post by orange808 »

While slightly more expensive, why not buy a cable at a trusted local shoppe with a good return policy?
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scrdcow
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Re: hdmi 2.1 optical cable latency

Post by scrdcow »

orange808 wrote:While slightly more expensive, why not buy a cable at a trusted local shoppe with a good return policy?
I live out in the woods, more or less. Without a car. We don't have any shops with optical long cables in any close city here :-) So I have to order online, and try to make sure I get it right the first time so I don't need to take any extra trips to town.
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orange808
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Re: hdmi 2.1 optical cable latency

Post by orange808 »

scrdcow wrote:
orange808 wrote:While slightly more expensive, why not buy a cable at a trusted local shoppe with a good return policy?
I live out in the woods, more or less. Without a car. We don't have any shops with optical long cables in any close city here :-) So I have to order online, and try to make sure I get it right the first time so I don't need to take any extra trips to town.
Fair enough, but you might still look elsewhere--away from Amazon. I simply don't trust Amazon for many things like: HDMI cables, shoes, sd cards, and SSDs. Too many dopplegangers and counterfeits. Good luck.
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Guspaz
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Re: hdmi 2.1 optical cable latency

Post by Guspaz »

NewSchoolBoxer wrote:tl;dr It doesn't matter what officially branded HDMI cable you use or what length it is unless we're talking over 25 feet, in which case you might need a Cat5E repeater. The length limit isn't due to latency but rather the voltage dropping enough that the high logic voltage level is interpreted as low logic voltage.
[...]
It's in his financial interest to plug expensive options versus perform due diligence and show a cheap yet effective solution. I don't mean to single him out, it's easy to point fingers at who's on top. It's a problem retro gaming-wide.
(NOTE: I'm going to use "HDMI 2.1" in this post, treat it as me saying "Ultra High Speed", meaning specifically 48 Gbps rated cables)

You can't use cat5e anything with HDMI 2.1, and there are no cheap yet effective solutions. The only way to do longer HDMI 2.1 runs is fiber optic, and those cables all cost a fortune.

I've been quite happy with Cable Matters' 15 meter (49.2 feet) HDMI 2.1 cable, which currently sells for $150 CAD.

HDMI 2.1 devices are very picky about cables, there are so many stories out there about people buying HDMI 2.1 cables and then not being able to do 4K120 over them because the cables aren't good enough. It's a major problem, especially for these fiber optic cables, and with HDMI 2.1, pretty much any cable longer than maybe 10-15 feet must be fiber optic to deliver the full 48 Gbps.

There are three things you should do when buying an HDMI 2.1 cable:

1) Only buy a cable that uses the specific wording "Ultra High Speed HDMI". Don't buy a cable that is labeled only as 4K or 8K or HDMI 2.1 or anything like that. If it doesn't specifically advertise "Ultra High Speed HDMI", ignore it.

2) Only buy certified Ultra High Speed cables. Make sure the cable is advertised as being certified. In the case of the Cable Matters ones, they both list "Certified" in the product entry, and advertise their certified status in the the marketing artwork on Amazon, and in the product description.

3) Once you get the cable, there will be an "Ultra High Speed" certification hologram and QR code on the box. Download the official "HDMI Cable Certification" app for your iPhone or Android phone and use it to validate the hologram. If the hologram is absent or does not pass verification, return the cable for a refund due to false advertising.

I think that if you follow these three steps, you can avoid the vast majority of issues with bad cables that fail to deliver actual 48 Gbps performance.
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scrdcow
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Re: hdmi 2.1 optical cable latency

Post by scrdcow »

Guspaz wrote: I think that if you follow these three steps, you can avoid the vast majority of issues with bad cables that fail to deliver actual 48 Gbps performance.
Yes, thtat's what I did. I still wonder about latency thou, not that I think there is much. But would still be nice to know if the conversion does much to it.
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Guspaz
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Re: hdmi 2.1 optical cable latency

Post by Guspaz »

I would not expect there to be any latency at all in a cable like this. They're not going to have a framebuffer, they're going to be converting the signal on the fly.
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scrdcow
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Re: hdmi 2.1 optical cable latency

Post by scrdcow »

Guspaz wrote:I would not expect there to be any latency at all in a cable like this. They're not going to have a framebuffer, they're going to be converting the signal on the fly.
True. Thanks for the help! <3
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Thomago
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Re: hdmi 2.1 optical cable latency

Post by Thomago »

:mrgreen:
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Guspaz
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Re: hdmi 2.1 optical cable latency

Post by Guspaz »

Are there even any cheaper options? I don't recall seeing any 48 Gbps HDMI repeaters, so AFAIK fiber is still the only way for long runs.
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ASDR
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Re: hdmi 2.1 optical cable latency

Post by ASDR »

I think all kinds of stuff like 48gbps / HDMI 2.1 repeaters or audio extractors / injectors don't exist, at least not as affordable consumer gear. It's all 2.0 / lower BW. Guess you could put an A/V receiver every 20m or so? :D
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system11
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Re: hdmi 2.1 optical cable latency

Post by system11 »

Removed drama posts.

It's not good form to suggest someone may have ulterior motives for suggesting a product unless you really have a lot of evidence to suggest it's the case.

I appreciate that most of the responses were positive.
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orange808
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Re: hdmi 2.1 optical cable latency

Post by orange808 »

I lost a fiber cable recently and I'm pretty sure it was because it was infrequently stepped on. Darn fragile for the price...
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Guspaz
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Re: hdmi 2.1 optical cable latency

Post by Guspaz »

That's probably where a lot of the difference between cables comes in... I'd imagine there are very few actual HDMI 2.1 copper-to-optical transceivers out there, so probably most of the cable vendors are using the same hardware, but there can still be significant differences in the quality of the cabling itself, particularly in terms of durability. The Cable Matters ones, for their part, have a fabric woven outer sheath and are quite thick/solid/stiff considering how tiny the fiber optic cabling inside of them must be. Like, they're way thicker and stiffer than my OM3 fiber cables. Of course I suspect they probably carry some signals over copper instead of fiber (maybe just using fiber for the TMDS/FRL links)? I'm just speculating baselessly though. I've not stepped on them since they're in a cable trough so I can't comment about how durable they are in rough environments, only that they seem like they would be reliable.
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