HDBaseT doubles down with V3.0
You’re probably well familiar with HDBaseT, and if you’re an AV integrator you’re likely using it fairly regularly. In fact, it’s been part of the common vernacular in our industry for a decade. But HDBaseT is undergoing its biggest upgrade since the introduction of the technology in 2010: the rolling out of HDBaseT version 3.0.
So, just what is it, and importantly, what does it mean for integrators? For those (like me) curious about the inner workings of technology, it might also raise other questions like how does it work, how much bandwidth is really needed, and what are the alternatives? I’ve been doing some research to answer these questions and several more, so here goes…
What is HDBaseT 3.0?
There’s a bunch of new capabilities with version 3.0, but the headline act is undoubtedly the doubling of uncompressed bandwidth to 16Gbps. That’s equivalent to 18Gbps in HDMI, meaning it can transport a full HDMI 2.0 AV signal (e.g., 4K/60 HDR or 4:4:4) without the need to decode or compress it.
Upstream traffic gets a massive boost too, up from 300Mbps to 2Gbps, mainly to enable full-duplex gigabit Ethernet (from 100MbE). The surplus is used for other things including USB 2.0, but I’d personally be really excited if manufacturers choose to also implement HDMI eARC as a native feature, but I guess we’ll have to wait and see.
Another difference that triggers my inner geek is the move from having separate transmitter and receiver chips to instead making it a transceiver. That is, the same chip can be configured for send or receive, the benefit of which really comes to the fore when you consider it being used in a switch — imagine instead of having a fixed dimension 4×4 matrix you could instead have an 8-port switch with all ports configurable for in OR out. Nice! But again, all in good time.
How does HDBaseT 3.0 work?
Part of the secret sauce of HDBaseT is the way it uses PAM16 — Pulse Amplitude Modulation, an advanced form of modulation similar to that used in 10G Ethernet — to squeeze a whole lot more bits over a limited bandwidth cable. When I first heard that HDBaseT bandwidth was doubling, I immediately wondered if they were going for an even higher PAM rate. Alas no, still PAM16, but doubling the sampling rate. Importantly, that also means doubling the bandwidth of the signal in the cable!
What cable is needed?
You’ll really need to use Cat 6A U/FTP to get the most out of the new spec, but I’ll add the caveat that you should always take the advice of your supplier/manufacturer for what’s most recommended for a given product.
So, why Cat 6A U/FTP specifically? Well, Cat 6A because its 500MHz bandwidth matches the operating frequency of the HDBaseT 3.0 signal. And U/FTP (as opposed to F/UTP as I’ve long advocated) because having each pair individually shielded means the cable can be made skewless. After all, unshielded cables use different twist rates on each of the four pairs to mitigate crosstalk, but when each is shielded, they can instead all use the same twist rate. This in turn results in tighter operating margins, and every bit helps.
Back up a moment… what happened to HDBaseT 2.0?
Did you happen to miss that there was even an HDBaseT version 2.0? Hey, I did that with at least three of the ‘Fast and Furious’ movies.
If you’ve undertaken the HDBaseT Installer Expert program or the new online HDBaseT Master program, then you’ll be aware of the differences. However, if your knowledge is based solely on practical experience then you might be less familiar, particularly if you work mostly in residential.
HDBaseT 2.0 has been out for several years, but to this day it’s still up to manufacturers whether they use version 1.0 or 2.0 in their products. Residential installs are still dominated by the original version 1.0, especially the more economical, shorter distance (70m at 1080p / 35m at 4K) solutions. Spec 2.0 is more popular in commercial settings, mostly due to it adding USB throughput, handy for things like keyboard and mouse extension. For the record, it’s also higher performing with more powerful processing and retransmit capabilities.
How much bandwidth do you need?
That’s a debatable question, particularly given that compression is getting so good. However, the main benefit with uncompressed is that of interoperability; devices have a far better chance of working together properly when there’s less complexity in the connection between them. Plus, decoding an HDMI signal in order to manipulate/compress it risks losing some embedded features like HDR metadata, among other things.
With HDMI we pretty much expect 18Gbps these days, although much of the time we don’t even need that. TV, streaming, and discs are most commonly 30fps or less, and all are 4:2:0. That means even at 4K UHD, HDR10 media will still fit through a 9Gbps HDMI signal (8.91Gbps, to be precise), but Dolby Vision typically needs more. It also changes as soon as the frame rate jumps to 60fps along with HDR, or if the source is a gaming console or GPU, wherein the step up to 18Gbps HDMI signal is essential.
HDBaseT can be considered at three bandwidth levels:
- 9Gbps HDMI signal uncompressed through HDBaseT 1.0/2.0 link,
- 18Gbps HDMI signal compressed to fit through HDBaseT 1.0/2.0 link,
- 18Gbps HDMI signal uncompressed through HDBaseT 3.0.
Manufacturers can implement option 2 above in a number of ways, all of which require signal manipulation. The HDBaseT approved method is to use VESA Display Stream Compression (DSC), being the same compression scheme that can be optionally used in HDMI 2.1 and DisplayPort 1.4 and 2.0. It’s true visually lossless (an abused term, but in this case they really mean it), and it’s real-time.
However, manufacturers can go it alone with their own method of light compression or alternative approach such as “colour space conversion” if they so choose, and many do. That’s fine in-principle, providing it’s understood and outcomes are predictable. For instance, being a closed system without cross-brand interoperability.
But as mentioned before, uncompressed gives the best possible chance for interop and retention of embedded features in the media, and that’s what HDBaseT 3.0 brings.
What about HDMI 2.1 through HDBaseT?
It’s still early days. Although the HDMI 2.1 specification has been out for four years, it’s taking some time for applications requiring its capabilities to roll out. I think the main reason is that most media is still happy at 18Gbps or less. There’s a few video features that will push it higher, including frame rates higher than 60Hz, or variable refresh rate (VRR) — think PS5 or Xbox Series X — or of course 8K. Theoretically, it’s logical to conceive using DSC as described above in conjunction with HDBaseT 3.0. For example, applying a 3:1 compression ratio to a 48Gbps signal would result in 16Gbps (there’s more to it than that, but let’s just talk simple maths). But again, I’m only theorising.
What are the alternatives?
The main alternative for long length uncompressed 18Gbps HDMI is optical fibre. This can take the form of industry standard, site terminable fibre with sophisticated electronics modules plugged in on each end, or the simpler, more pragmatic pre-terminated HDMI active optical cable (AOC). In both cases, performance and interoperability is determined by the electronics at each end, including bandwidth as determined by laser speeds. The best examples can support the full 48Gbps data rate of HDMI 2.1.
However, a big consideration with HDMI AOCs is the handling of the HDMI Display Data Channel (DDC). Okay, maybe your eyes start to glaze over as you try to stifle a yawn, but please bear with me… it’s important! DDC always has and is still the most important channel in HDMI. DDC is where the HDMI handshake occurs — it’s the channel by which the source reads the display’s EDID, it’s where HDCP exchange happens, and it’s where devices can agree on HDMI version capabilities and link speed. Little has changed electrically with DDC since the inception of HDMI, and it remains the number one source of errors and troubleshooting.
When using HDMI AOC, ask how the DDC is handled. Many cables use fibres for the high-speed lanes but still use copper for DDC and other auxiliaries. If the length is more than about 10m you’d ideally want some form of active augmentation for the DDC to ensure the many signals can go the distance. This is the main reason I advise integrators to bench-test such cables with the equipment they intend to use it with to ensure interoperability.
By comparison, HDBaseT serves as a bit-exact transport for DDC over 100m, effectively remaining transparent to the devices at each end.
Bottom line — what does HDBaseT 3.0 mean for integrators?
It means more options, which is good news. HDBaseT 3.0 can deliver double the bandwidth of earlier versions, which is indisputably better for AV performance and system interoperability. But it requires some know-how and attention to detail in ensuring the installation particulars are optimized for it, such as using Cat 6A U/FTP, and terminating it well!
As always, my advice is to stay educated about the AV parameters and features in order to define expectations for the transport system. Then work with your supplier partners in understanding what equipment and supporting infrastructure is needed for installation success.