Latency vs Longer cables

[przecinek]

Ok this is just a quick thing I wanted to ask.

Unfortunately I don't have a latency tester but do you reckon longer VGA cable could contribute to an increased latency?

What I want to do is run an extension trough my ceiling lamp, so that I can turn and move around more easily.

Other than that I already switched from duplicate to extended mode -> it can make a difference (combined with motion blur) and switched both screens to 1280 x 800 to avoid scaling. It seems I am prone to latency related VR sickness.

Anyway, I am just imagining that a 5 meter cable can contribute to increased latency?

[colocolo]

Ok this is just a quick thing I wanted to ask.

Unfortunately I don't have a latency tester but do you reckon longer VGA cable could contribute to an increased latency?

What I want to do is run an extension trough my ceiling lamp, so that I can turn and move around more easily.

Other than that I already switched from duplicate to extended mode -> it can make a difference (combined with motion blur) and switched both screens to 1280 x 800 to avoid scaling. It seems I am prone to latency related VR sickness.

Anyway, I am just imagining that a 5 meter cable can contribute to increased latency?

well, i dont know much about electronics, but shouldnt the signals travel with 1/3 c through the cables? it shouldn't have an impact then.

[Ziggurat]

Ok this is just a quick thing I wanted to ask.

Unfortunately I don't have a latency tester but do you reckon longer VGA cable could contribute to an increased latency?

What I want to do is run an extension trough my ceiling lamp, so that I can turn and move around more easily.

Other than that I already switched from duplicate to extended mode -> it can make a difference (combined with motion blur) and switched both screens to 1280 x 800 to avoid scaling. It seems I am prone to latency related VR sickness.

Anyway, I am just imagining that a 5 meter cable can contribute to increased latency?

well, i dont know much about electronics, but shouldnt the signals travel with 1/3 c through the cables? it shouldn't have an impact then.

You are correct, but that does not take into account magnetic interference. So in theory if the wires are well shielded you should be fine. Repeaters can add latency though.

[geekmaster]

Ok this is just a quick thing I wanted to ask.

Unfortunately I don't have a latency tester but do you reckon longer VGA cable could contribute to an increased latency?

What I want to do is run an extension trough my ceiling lamp, so that I can turn and move around more easily.

Other than that I already switched from duplicate to extended mode -> it can make a difference (combined with motion blur) and switched both screens to 1280 x 800 to avoid scaling. It seems I am prone to latency related VR sickness.

Anyway, I am just imagining that a 5 meter cable can contribute to increased latency?

The Rift does not support VGA. It supports DVI and HDMI. For resolutions of 1280x1024 and below (as used by the Rift), Single-Link DVI cables may be up to 50-feet long.

Electric signals travel at the speed of light in a vacuum, and slightly slower in electrical signalling cables (due to cable velocity factor).

The speed at which energy or signals travel down a cable is actually the speed of the electromagnetic wave, not the movement of electrons. Electromagnetic wave propagation is fast and depends on the dielectric constant of the material. In a vacuum the wave travels at the speed of light and almost that fast in air. Propagation speed is affected by insulation, so that in an unshielded copper conductor ranges 95 to 97% that of the speed of light, while in a typical coaxial cable it is about 66% of the speed of light. ... the velocity of propagation is very high — about 300,000 kilometers per second ...

So, assuming that twisted-pair cables behave similar to coaxial cable, a 50-foot cable would cause a signal delay of less than 60 nanoseconds. A good rule of thumb I learned as a child was that electricity travels about 9-inches per nanosecond in copper wires, which confirms this estimate.

Comparing to recommended latency for VR, the video cable could be more than a million times longer than those shipped with the Rift, before latency would become an issue. However, the DVI specification limits the length to 50-feet before DVI repeaters are required to extend the signal.

Latency can be caused by other factors, such as the video signalling protocol implementation itself, but not by cable length.

EDIT: I see that TWO people pressed their Submit button while I was editing my post.

well, i dont know much about electronics, but shouldnt the signals travel with 1/3 c through the cables? it shouldn't have an impact then.

You are correct, but that does not take into account magnetic interference. So in theory if the wires are well shielded you should be fine. Repeaters can add latency though.

@colocolo: Your speed estimate was close, but a bit off. According to WikiPedia, electricity travels at about 2/3 c (or faster, up to 97% c) in a cable.

@Ziggurat: Although magnetic interference may corrupt a signal from induced electric current in the cable conductors (perhaps reducing the maximum useful cable length in a magnetically harsh environment), it should not affect the speed of electric wave propagation in the cable. Also, DVI repeaters are typically just line distribution amplifiers (with analog equalization) that support full specified DVI frequency, so they do not add any measurable latency of their own.

EDIT2: One reported source of latency can be caused by routing both video and audio over an HDMI cable, and some HDMI switches are also known to cause latency issues from storing and forwarding video data packets. These issues do not generally affect DVI devices.

[Direlight]

Are there really video cards out there that only have VGA? And you're trying to run Rift games on such a low end card? Am I missing something?


If it's on an old laptop, lag is a minor issue compared to your fps in anything other then maybe the quake ports.

[geekmaster]

Although you can buy VGA-to-DVI adapters, they contain three high-speed analog to digital converters and are quite expensive (typically about $130 or so). Also, the digitizer function can add latency. Better to spend that money on a computer upgrade.

[Direlight]

gtx670 (or AMD equivalent) is needed or higher for Star Citizen according to Chris Roberts. Why is that relevant? Everyone knows if your computer runs latest cryengine it will run literally every other game, except maybe NASA supercomputer sims. lol

[przecinek]

Thanks for the reply guys. I'm a bit of a cheapskate really. HL2 will run on almost anything really and I don't really play games that much anyway.

Anyway forget the VGA part as this wasn't really my point ... Just wanted to make sure that signal strength doesn't influence latency in any way

The setup that I have created is a bit problematic ... You can't extend the cord that goes from OC into the control box ... so even with a 5m video cable the control box is still hanging in the air along with USB and power cables. I'm a bit dissapointed that you can't detach HMD from the control box without taking the rift apart.

Edit: Here's what it looks like Allows you to have a 360 degree freedom without fear of getting entangled but with everything hanging in the air it's far from perfect.

[Fredz]

Although you can buy VGA-to-DVI adapters, they contain three high-speed analog to digital converters and are quite expensive (typically about $130 or so).

You may have forgotten about this one ($31) : http://www.mtbs3d.com/phpBB/viewtopic.php?f=140&t=17975

[geekmaster]

Although you can buy VGA-to-DVI adapters, they contain three high-speed analog to digital converters and are quite expensive (typically about $130 or so).

You may have forgotten about this one ($31) : http://www.mtbs3d.com/phpBB/viewtopic.php?f=140&t=17975

Actually, I did forget that one, which is odd because I ordered one and mine has been shipped (but not yet received). That $31 converter is an excellent price, if it works as well as I hope it does (no "show-stopper" latency).