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 Lag and long HDMI cables 
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Two Eyed Hopeful

Joined: Fri Feb 11, 2011 5:49 am
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I've recently changed my computer setup at home and I'm likely to put a Long HDMI cable through from the office to the living room, so I can game there when needed.

However before I run any cables through the wall I just wanted to check if this would add any lag to the setup? (anyone know any specifics ie ms/feet?)

As I'm likely to do the majority of my gaming as VR based by the end of this year it's becoming an even more important question for me than it might have been before.

So in theory the signal should travel by the speed of light so any additional lag would be effectively nil. However is that actually true in practice with a real cable, are we talking of the order of picoseconds additional lag for a 40ft run?


Wed Jan 22, 2014 3:46 pm
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Petrif-Eyed
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yunti wrote:
I've recently changed my computer setup at home and I'm likely to put a Long HDMI cable through from the office to the living room, so I can game there when needed.

However before I run any cables through the wall I just wanted to check if this would add any lag to the setup? (anyone know any specifics ie ms/feet?)

As I'm likely to do the majority of my gaming as VR based by the end of this year it's becoming an even more important question for me than it might have been before.

So in theory the signal should travel by the speed of light so any additional lag would be effectively nil. However is that actually true in practice with a real cable, are we talking of the order of picoseconds additional lag for a 40ft run?
Cable length does not affect lag in any perceptable way. The signal travels through the HDMI cable at about two-thirds of the velocity of light, and HDMI cables can be up to 50 feet long before they need a repeater to extend the length.

So, to answer your "specific" question regarding ms/feet, that calculates out to 0.00000167 ms/ft (i.e. picoseconds, just as you mentioned.

EDIT: According to this, HDMI velocity factor is about 0.73, so the actual lag is even smaller than I mentioned above:
http://sommercable.com/2__produkte/2__0 ... _0241.html

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Wed Jan 22, 2014 4:41 pm
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Binocular Vision CONFIRMED!
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I run a 50' HDMI cable from the basement to my 2nd story bedroom. No perceptable lag.


Thu Jan 23, 2014 10:29 am
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Two Eyed Hopeful

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geekmaster wrote:
Cable length does not affect lag in any perceptable way. The signal travels through the HDMI cable at about two-thirds of the velocity of light, and HDMI cables can be up to 50 feet long before they need a repeater to extend the length.

So, to answer your "specific" question regarding ms/feet, that calculates out to 0.00000167 ms/ft (i.e. picoseconds, just as you mentioned.

EDIT: According to this, HDMI velocity factor is about 0.73, so the actual lag is even smaller than I mentioned above:
http://sommercable.com/2__produkte/2__0 ... _0241.html


Geekmaster that's just the answer I was hoping for thanks. I was keen to know if the real world test wasn't too different to the theoretical speed of light, but thanks for that link to confirm.

Definitely nothing to worry about if it's only a fractional impact on c.

Thanks.


Thu Jan 23, 2014 4:07 pm
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Golden Eyed Wiseman! (or woman!)

Joined: Fri Jul 08, 2011 11:47 pm
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I've had issues with long HDMI cables. Ran one at my parents for their computer to their TV, kept dropping out (black screen for a split second) every minute or two.
I bought another cable, it works fine, very occasionally the sound will skip a little though.

My conclusion was that if you want a long HDMI cable, don't buy the cheapest cables out there (like I did). I suspect that there is a quality difference that might only matter when you are using longer runs.


Fri Jan 24, 2014 1:38 am
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Petrif-Eyed
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WiredEarp wrote:
I've had issues with long HDMI cables. Ran one at my parents for their computer to their TV, kept dropping out (black screen for a split second) every minute or two.
I bought another cable, it works fine, very occasionally the sound will skip a little though.

My conclusion was that if you want a long HDMI cable, don't buy the cheapest cables out there (like I did). I suspect that there is a quality difference that might only matter when you are using longer runs.
Cheap cables can have significant signal loss (too low a voltage) if they are too long for cable quality. For long length, a good quality cable is important.

However, low signal strength causes dropouts (corrupted packets), not latency. For very long lengths, you can use a repeater that amplifies the signal (increasing its voltage and or adding digital threshold), which can add negligible latency if it provides analog amplification, but can add significant latency if it is a repeater that resends the packet after it is fully received.

Cheap cables may be fine for a short length (a couple meters or less), but for 50 feet, I recommend a high quality (i.e. not cheap) cable. Also, you must avoid kinks and crushes (such as from bending a cable too sharply, or stepping on it), as that can damage the cable to cause signal reflections and attenuation that degrade the signal, perhaps causing signal dropouts. Also, running the cable too close to power lines, fluorescent lights, or other sources of electrical interference, can degrade the signal (i.e. do not run them side-by-side, or in the same conduit, with power line cables).

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Fri Jan 24, 2014 2:50 pm
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Two Eyed Hopeful
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Ok so for example this extender : http://www.amazon.com/Generic-HDMI-Repe ... B00JZL1RVG

Will add some latency as it "regenerates the incoming HDMI signal by decoding and re-encoding it"?


Tue Jan 06, 2015 8:41 am
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http://www.reddit.com/r/oculus/comments ... to_oculus/

It did cost a premium price but it works like it should! So for anyone that is in the same situation that I was in, I would totally reccomend the ATEN HDMI Extender VE800, just remember to try out the different EQ settings till it works. Direct mode and Extended mode works just as it should and I am so excited to be back!

Lots of good info in that thread, and seems even using oculus cable was causing some guy an issue:

[–]BOLL7708 3 points 2 days ago
Very interesting indeed :P Are you still using the stock HDMI cable at the end, or have you routed a custom HDMI all the way to the HMD? Only adding extensions to the default cable has given me issues similar to yours, but I'm running with a 1m extension now to get the cable box on my desk and that works just fine.
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[–]Webdriver[S] 2 points 2 days ago
I am indeed using the original cable! Because of the way the original cable is built (Very thin and fragile), the signal didnt quite reach the headset itself since the cable was so thin. But even though that I replaced the cable, it would still be unplayable.
My current setup is kinda messy right now, I tried to make it clean and hide the stuff, but atleast it works with everything original. (All those 3 cables that are together are the original DK2 cables with USB, HDMI and Sync.
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[–]BOLL7708 1 point 2 days ago
Wuh... there are actually three cables in the combined cord? O.o I thought the sync was somehow baked into the USB as well, only USB and HDMI enter the headset! Does two of the cables terminate in a single USB plug? I realize I have not seen the thing picked apart :P just figured it was the two...
Edit: Oh, right, those cables come out of the cable box... doh! It's late here, I'm tired xD
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[–]Frammish 4 points 2 days ago
ThinkLogical has fiber optic HDMI/DVI extenders that are expensive but work great. For commercial/professional use, they would also be a good choice.

The stories I could tell back in the day at IBM of cable runs on token ring networks! LOL! I vividly recall pat everhart calling us in for a meeting because so many clients were complaining that ethernet solutions with just a few computers were faster than the token ring solutions - our internal tests verified with just a few computers the collissions were not great enough to be better than ethernet, token ring only really helped with many computers. http://www.networkworld.com/article/228 ... -ring.html We spent MORE DILBERT BOSS MEETINGS going through how we could not talk about this, and deny this to our clients, yada yada yada, what a waste of time, I spent 80% of my time in meetings at IBM that achieved NOTHING! Wanted to get back to my terminal and play minesweeper! LOL!

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Tue Jan 06, 2015 4:47 pm
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Binocular Vision CONFIRMED!
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I am some guy, and funny enough I was subscribed to this thread!

My issues seems to have been caused by using a DVI to HDMI cable and then the included cable in a series, that would generate strange color artifacts etc. Using the included cable directly worked just fine though.

Now my new(ish) GTX970 actually has a full size HDMI port so I'm running a short extension and the included cable after that with no issues.


Tue Jan 06, 2015 5:37 pm
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Boll welcome back! The internet is a fascinating place, so much information everywhere, but to get to it, get the answers, such a treasure hunt! The oculus cable is a special Dr. Dre Beats Palmer Luckey gold series endorsed cable! LOL! http://i.imgur.com/5PwRMhN.png spectra7 vr7100 processor in it! Oh the tangled web we weev! ;) Now if we can just get KBK and geekmaster talking about cables again and waves going through inflection points! BWAHAHAH! Or something like that, hell i forget!

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Tue Jan 06, 2015 7:38 pm
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Cross Eyed!
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What about this:

http://lifehacker.com/5918457/hdmi-over ... aves-money

I think it is working, long enough and cheap. Do you have some experience with it?


Wed Jan 07, 2015 4:26 am
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