VR PSA – Check Your Cable Setup When Using Extensions

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    Date Posted:
    Jun. 03, 2020
    Last Updated:
    Jun. 03, 2020
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Disclaimer: This post contains several Amazon affiliate links.

I’m writing this post because I really wish someone had warned me about this when I first bought my VR headset (a WMR Samsung Odyssey+), and if they had, it would have saved me a lot grief. For a while now, I’ve been struggling to overcome certain issues with the headset, such as unreliable tracking and random glitches.

Windows Mixed Reality (WMR) - Lost Boundary Error Message

I think I finally just found the culprit, an underpowered cable setup, and this post was written as a guide to explain the issue, as well as solutions for properly extending VR cables without introducing issues.

Discovering the Issue:

These random glitches and tracking issues had been getting worse and worse recently, and at a certain point the headset felt unusable.

At that point, while troubleshooting everything I could possibly think of, I tried plugging the headset directly into the computer (no extension cables), and BAM – it started working a million times better. No tracking issues, no lost boundaries, and no glitches.

The Issue:

Like many other VR headsets, the Samsung Odyssey’s cable is really too short (4 meters / 13.1 feet) for comfortable room-scale play, so shortly after I bought it, I also bought and started using a 10 foot USB 3.0 extension cable. At the time, I didn’t think much about adding it to my setup – I knew at least that it was important to use 3.0 (or, more likely, a 3.1 variant) instead of 2.0, since VR needs the higher data speed and throughput, and this cable satisfied that need, so I thought I was good to go. Heck, the cable even advertises itself as being “for … VR Headset(s)”.

However, it’s not that simple. See, like many people, I was unaware that the recommended maximum length for a run of USB 3.0/3.1 cable is only about 3 meters (9.8 feet)(!), depending on cable thickness. The cable from the VR headset already exceeds that length, so adding an extension cable puts it way over the recommended limit, and explains why removing the extension cable suddenly fixed all my issues.

The Fix – Ways to Properly Extend VR USB Cables

Playing with the headset directly plugged into the computer without extension cables obviously works the best, but it is not practical for room-scale games, or even most standing games for that matter. So how can we extend the cable without exceeding the limits? It depends.

  • Best overall solution: HTV Vive Link Box (Amazon product page, Official Product Page)
    • Pros:
      • Multi-purpose: repeats both USB and HDMI signals, as well as converts DisplayPort to HDMI
      • High quality: You can check out the internals in this teardown. For example, the USB hub chip is a Microchip USB5744, which supports full USB 3.1 Gen 1 speeds.
      • Great for mounting on ceiling, as single repeater for both HDMI and USB cable
      • Built-in Bluetooth, in case your computer doesn’t already have it
    • Cons:
      • Pricey
      • Requires a separate power adapter (see below)
      • Requires a separate male-to-male USB cable
  • Powered USB 3.0 Hub (Amazon search results)
    • Pros:
      • Relatively inexpensive, ~$10-20 for most
      • You might already have one laying around
    • Cons:
      • Won’t repeat / extend HDMI connection
      • Requires an electrical outlet
  • “Active Extension Cable” (Amazon search results)
    • Pros:
      • Some are self-powered (over the same USB connection it is extending)
      • Less clutter (single cable, instead of a connecting box)
    • Cons:
      • Tends to have way more issues than alternatives that are externally powered, especially with VR headsets – see my explanation as to why, below
        • Externally-powered ones, like this one, tend to work better, but require an extra power cable, so you might as well just get a powered hub
      • Self-powered models only boosts signal, not voltage
      • Can have limited or no support for backwards compatibility (USB 2.0) or variation in spec
      • Often limited in disclosing the full specifications of their product

As great as the Vive Link Box is, a major drawback is that it does not come with a power adapter, and finding a suitable one to use with it actually took me a while.

To save you the same hassle, I’ll warn you that you will likely not be able to find an original AC adapter for sale (at least not “new”), and the requirements are as follows:

  • 12V (DC)
  • 1.5A (minimum)
  • Center Positive Polarity
  • Barrel Jack Size: 3.5mm x 1.35mm

With these requirements in mind, I ended up getting this adapter, and so far it has been working great. The most unique thing about the adapter is the barrel jack size; it is much easier to find 5.5 x 2.1mm 12V adapters, and then purchase a size adapter, like this 2 pack.

Thank you to these Reddit threads for providing details: this one, and especially this one (power adapter answers)

Issue With Self-Powered “Active Extenders”

There are a bunch of cables on Amazon that don’t require external power adapter, unlike USB hubs or the Vive Link Box, but still call themselves things like “Signal Booster”, “Active Extender Cable”, and “Active Repeater Cable”. Although these aren’t “snake oil” products, the way they work can have some negative consequences for VR applications.

Most of these cables include some sort of repeater IC (Integrated Circuit) chip, built into the cable itself. Usually this is noticeable, because one end of the cable will be very bulky to accommodate the IC circuit. To power these circuits, the cable basically siphons current from it’s own wiring – the connection it is extending.

This is often referred to as being “bus powered”, since the power is drawn from the computer’s USB bus, rather than an external power source.

For many devices, these cables work fine. However, VR devices tend to have very tight requirements and tolerances, since their main concern is latency; delivering an image with an added 10ms of delay (that’s just 0.01 of a second) can be the difference between a great VR experience, and one that makes you feel like you are going to throw up from motion sickness.

To get back to the issue, there are two major problems with these types of cables:

  1. Those repeater chips (often called “redrivers”) often only need a small amount of power to be siphoned off. For example, the NXP PTN36241B, which is used in the CableCreation 16.4 Foot Active Extender, only requires about 100ma of current while active, although the circuit integrating the chip probably draws a little over that. 100ma is not much, but the VR headset itself also draws a significant amount of power, to run the displays and assorted circuits, and it can be the case that there simply is not 100ma to spare, especially if you have an older computer with a low maximum supply current for USB.
    • This is an issue for the Samsung Oyssey+ in particular, because of how much current the device draws. The Odyssey and Odyssey+ draw about 900ma, which is right at the border of what the USB spec says a port is required to provide.
  2. The “bus powered” repeater chips boost the data signal strength, but do not usually boost the voltage, since realistically this would require an external power supply (to handle the current required by the boost circuit itself). This can be a big problem, because voltage will naturally drop as a cable extends in length, and many VR headsets are not tolerant of lower voltage supplies.
    • For example, in a 16 foot run of USB cable, without a voltage boost, the voltage drop could easily exceed 0.5v, which could be outside the USB specifications, and likely to to cause issues with a VR headset
    • Normally, your motherboard and USB port can adjust to compensate for a voltage drop, but combined with the issue above, it might not be able to with the load of both the repeater and headset running

These two limitations of self-powered repeaters, especially when combined, are often deal-breakers for VR headsets. To this point, note the small FAQ section the product page linked above for the CableCreation active extender:

Q: Does this extension work Samsung Odyssey VR?

A: Yes, but because of the extended length […] you need to connect a powered USB hub or adapter for external power supply.

So, if you buy a self-powered repeater cable, you might also have to buy a powered USB hub to plug it into, which kind of defeats the purpose…

Sensors VS Headsets

You might be wondering why on a lot of Amazon reviews for various extenders / repeaters / cables, you see a common pattern where there are positive reviews saying “this worked great for ____ VR sensor!”, but also negative reviews of “this didn’t work at all with ___ VR headset”.

The reasons for this are pretty simple:

  • Sensors usually require a lot less total throughput, compared with a headset (which also often has built-in sensors itself)
  • Sensors require much less power than headsets, since they aren’t driving bright displays combined with audio, processors, and more.
  • Sensors often have greater tolerances for different types of hosts (for example, the Rift Sensor can work over USB 2.0 in addition to 3.0, whereas most headsets require 3.0)

In general, a standalone sensor just requires a lot less “stuff” to function, in comparison to a headset, which is built with a bunch of sensors, plus dozens (if not hundreds) of other components.

Samsung Odyssey and Odyssey+ Peculiarities

I’ve touched on this above, in various sections, but I think part of why the Samsung Odyssey+ in particular seems to have so many users complaining about issues with extending USB length is because the device was built to basically be right at the edge of all “maximums”, out of the box. For example:

  • Various manuals and webpages make it sound like the device absolutely needs a full 900ma to function. That is literally the maximum required by the USB 3.0 spec.
    • USB ports are free to supply more than that amount, but are not required to, and it is up to the PC manufacturer.
  • Various sources also make it sound like the Odyssey is not tolerant of voltage drops; e.g. it needs the USB supply voltage to be as close to 5V as possible
    • This is especially problematic since the Odyssey+ comes with a 4 meter (13.1 feet) USB cable, which is already long enough to be in the danger zone (or right at the edge) for causing voltage drops. It helps that the USB cable is thicker than most.

Disclaimer: I’m not an Electrical Engineer, so most of this is based on quick research, not prior knowledge.

These Reddit threads (1, 2, 3, 4) are good examples of what I mean by this being a common issue for Odyssey users (who could probably benefit from my advice on this page).

Why Is HDMI Less of An Issue?

You might be wondering why, so far, I have written pretty much exclusively around how extending USB is an issue, and doing it incorrectly leads to issues with VR headsets. Why not HDMI as well?

I’m not on expert on these things, but I think I can simplify without being incorrect, in saying that extending the HDMI cable with VR headsets is generally not as much of an issue as USB because of the following two factors:

  1. HDMI has a longer maximum length than USB to start with
    • There is not a specific maximum length put forward in a standardized HDMI spec, but generally, 25-50 feet is considered the maximum, without a repeater.
    • In comparison, a standard thickness (24-28 awg) USB 3.0 cable should not exceed somewhere around 10 feet.
  2. HDMI is being used for less things than USB, on a VR HMD
    • With a standard VR headset, HDMI carries the video feed, and maybe the audio feed. This data (mostly) only has to flow in one direction, and there is some tolerance built-in
    • USB, on the other hand, is carrying the power supply, sync data, microphone feeds, and sensor data. Sensor data could be multiple bi-directional feeds, encompassing live cameras, accelerometers, gyroscopes, compasses, and more. Many of these pieces of data have to be delivered with minimum latency, as any delay will increase the risk of motion sickness.

Having said all that, extending the HDMI cable could still be an issue for you, either over longer lengths or with thinner cables, which is why I still recommend the Vive Link Box as the best extender solution, since it extends both the USB and HDMI connection in one device.

TLDR

Here is the TLDR of this post; if your VR headset frequently has tracking issues, loses boundaries, or other random glitches, take the time to check your cable setup and make sure you are providing enough power for the length of cable used.

List of symptoms that could appear with cable length issues:

  • Frequent “lost boundary” error message and/or room starts spinning
  • Controllers lose tracking and start floating randomly
    • Tends to happen with fast games, like Beat Saber
  • “phantom” controller input; random key presses and trigger pulls
    • This one also seems to be caused by sunlight and/or reflective surfaces around the play area
  • Entire headset randomly restarts
    • Especially when cable is moved
  • Headset takes a long time to recognize environment and/or sync with controllers
  • Random audio “hiss” or “static” noise

Best ways to extend cable length without issues:

  • Use a powered repeater box (powered USB 3.0 hub, or “Vive Link Box”)
  • Use cables marked as “Active Extension” and/or “Active Repeater”, especially those that require external power sources

Extra Troubleshooting

  • Make sure your USB cable is plugged into a 3.0/3.1 port. Usually, these are marked with a “SS” logo, for SuperSpeed.
    • If your PC has any USB ports labeled “high power” or something like that, switch your VR headset over to that port
  • Make sure you are using an HDMI connection to match the requirements of your HMD, usually 2.0
  • Check that controllers are charged up
  • Check for firmware updates
  • Try re-pairing controllers
  • Make sure your play area is well-lit, but not with sunlight, and is free of reflective surfaces

Extra Reading

If you are nerdy like I am (🤓), you might share my interest in these resources that I came across while writing this:

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