Original Link: http://www.anandtech.com/show/1589




Talk about HDMI

So, more specifically, what is HDMI? HDMI - High Definition Multimedia Interface - is actually just a logical progression on top of DVI. The video segment of the HDMI signal is actually compatible pin for pin with DVI, but in a much different package. HDMI improves on DVI by transmitting digital audio on the same interface, adding support for HDCP and also better DDC options for manufacturers.

HDMI provides 5Gbps over copper interconnects up to 15 feet - that's enough headroom for a 1080p signal and 8 channel audio. For those who like to do the math, a 1080p raw video signal and eight 192kHz audio channels require less than 4Gbps. So, there is a significant portion of unused overhead built into the HDMI specification. We've seen demonstrations of hooking your DVD player, receiver, and PVR each with a single cable at shows like CES and the word is that adoption of HDMI is going even faster than originally planned.

Below, you can see a cross-section of what the 19-pin HDMI cable looks like. The smaller, sturdier cable was designed with laptops and slimmer devices in mind. The DVI cable on the right shows the large difference in size.


Click to enlarge.

Right now, HDMI cables, like the original DVI cables, are very expensive. High quality cables easily retail for more than $100 each, although middle of the pack HDMI cables in the one and two meter range can be had for less than $20.

Remember the interoperability and quality issues with older DVI connectors on video cards? Since DVI is a relatively loose protocol, manufacturers are not strictly enforced to adhere to design principles. Signal quality on DVI connectors hit a low point in 2001/2002, but fortunately, it seems that awareness of the problem has started to rectify these issues. Since Silicon Image had a significant influence on the original DVI and HDMI specifications, they have taken it upon themselves to set up their own quality control laboratories, PanelLink Cinema (PLC). New devices will go through a very stringent verification process to assure that the next generation interfaces don't have the same problems which plagued DVI. The lab also works directly with Intel's HDCP spinoff licensor, Digital Content Protection, to assure that HDMI-ready devices adhere to the HDCP guidelines. Copy protection is a large facet in the HDMI specification, so it only makes sense that Intel and Silicon Image have so much invested in building trust with the content providers.

Today, the largest factor that plagues HDMI in the living room is whether or not devices are actually taking advantage of 8 channel audio. Many of the first generation HDMI ready devices only utilized two channels with the thought that TVs in particular would not need anymore than 2 channels. As a result, many new devices still ship with separate stereo inputs just as they do with DVI, but obviously, the push will be for new devices to drop these inputs in favor of digitally-protected high fidelity capabilities built in the cable specification. Stereo would just be a fall back.




Significance on Desktop

The first question that should pop into your head right now is why we would need HDMI on the PC when it physically does the job of DVI – particularly considering how few people actually use DVI instead of analog connections! The answer is, again, copy protection. If we take a step back and look at the larger plans for PCs and media devices in general, the obvious trend becomes the PC’s integral role as an entire entertainment system with considerable weight on Media Center, DVDs, etc. For large content providers like Viacom, Starz! and Discovery Channel to get on board with Microsoft’s dream of IP TV, media center “servers” and set top boxes running stripped-down PC hardware, the obvious scrutiny on security comes to mind as well. No major content providers would consider the Media Center vision if they didn’t feel that their content would be secure from piracy on MCE PCs.

The weakest link narrows down to the user’s ability to transcode on demand media on the PC into something more portable, or the user’s ability to digitally rip the signal off the DVI interface! With Intel’s HDCP tied into the HDMI specification so tightly, manufacturers and content providers would be insane not to push HDMI out the door to replace DVI. The additional perks for HDMI are still there: it’s a smaller cable, can run longer distances without issues, and obviously, the integrated ability to transfer audio too. However, when a tier 1 OEM decides to build their next HTPC, they will certainly come under considerable scrutiny to provide a secure platform if they expect backing from the content providers. The fact that HDMI protects video and audio signaling is enough for content providers to lean on PC manufacturers to adopt the standard over DVI.

Audio poses a fairly large problem for PC manufacturers. While it’s easy for an IGP motherboard to include audio and video on the same interface, graphics cards are only designed for video. At first, graphics cards and motherboards that adopt HDMI will probably opt out of utilizing audio over HDMI as most HDMI-ready devices allow analog stereo input (just as DVI does). However, if we think more long term, fusing audio and video on the same output puts ATI and NVIDIA at particular odds with discreet and integrated audio partners. After all, Intel just released their 8 channel digital audio solution, and companies like Creative and VIA have a significant portion of their business riding on the fact that separate inputs are needed for audio and video. Will we see a synergy from graphics and audio manufacturers to consolidate audio and video back down onto the graphics card? Unfortunately, the PC industry doesn’t have an answer for that question just yet.

Where does this leave DVI? For the PC industry, DVI is just getting its feet off the ground in terms of replacing the ancient 15-pin D-sub analog cables that we have all been using on CRT monitors. There isn’t an advantage for the everyday home user to need an HDCP compliant HDMI LCD panel connected to their computer, although with the backing of a player like Microsoft, it won’t be very long before HDMI starts showing up anyway. For the home theater industry, HDMI is already here and quickly gaining a lot of momentum. DVI won’t disappear overnight in the living room, but you can surely bet that the content providers would love to remove its weakest link in digital copy protection in the near future. Not surprisingly, FCC just mandated that all digital cable ready TVs sold after July 2005 must have DVI-HDCP or HDMI-HDCP capability.

All in all, be aware of the new standard, but don’t be too surprised if HDMI starts showing up on next generation IGP motherboards and then, finally, video cards with audio capabilities. HDMI-to-DVI converters will continue to support older TVs and monitors that don’t have HDMI capability if that monitor is HDCP compatible. The smaller form factor is a welcomed addition for laptops and set top HTPCs, and if audio integration takes off, it will be a welcome fix to the clutter behind the computer. If the PC market shows the same momentum for HDMI that the home theater market has, it certainly won’t be too long until we get these questions answered first hand!


Log in

Don't have an account? Sign up now