There might not be much difference in terms of video bandwidth, but HDMI has a stack of features, like carrying audio, that give it the edge over DVI.
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Big and No Remote Support
For a while, along with PC users, people at the sharp end of home theaters were using DVI cables. When high definition video players and TVs began to gain popularity, the DVI connector was a proven solution for transmitting digital video signals (not the DV spec; I mean video signals which are digital, as opposed to video signals which are analog) in PCs. It was incorporated into high-end video equipment with some success, but there were problems.
While computer users are accustomed to dealing with connectors that have pins and screws, a DVI connector is large and unwieldy by home theater standards. It also has no provision to carry control commands (play, pause, volume, etc) from one device to another. This continues the tradition of having to use multiple remote controls, or programming codes into universal remote controls and switching functions, to control various home theater devices.
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How Many Cables?
Another problem is the number of cables required. A computer’s video and audio signals usually come from separate sources, and go to separate peripherals. One connection is (or several are) made between graphics card and monitor, another (or several others) between sound card and speakers. Similarly, a home theater receiver sends audio signals to an amplifier, and video signals to a screen. Again, one cable (or a set of cables) goes to one device and another cable (or set of cables) goes to the other.
A DVD player, though, is a single source for both audio and video, and connects to a single device, the receiver. The number of cables needed to connect one device to another (ignoring wireless connections) is, ideally: one. Connecting a mouse or keyboard to a PC doesn’t require hooking up several cables, after all. Connecting a DVD player with DVI, however, involves not only the DVI cable, but a separate cable (or, again, set of cables) to carry audio.
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HDMI Much Easier to Use
HDMI devices, like DVI devices, can, but don’t have to, support HDCP. Unlike DVI devices, HDMI devices almost universally include HDCP. But it doesn’t hurt to make sure.
HDMI connectors are smaller than DVI ones, and don’t use screws. They are backwards compatible with DVI connectors, requiring only a passive (meaning just wires, no processing) adapter to maintain all the functionality of a DVI connection.
Also, they can carry high quality digital audio at the same time as video. Thus, they can replace co-axial or optical digital audio connectors. This means you can connect a high-end DVD player to a receiver using a single cable, without loosing any audio or video quality - in theory.
In practice: if the Digital Analog Converter (DAC) in the source device is nicer than the DAC in the receiver; it is preferable to do the conversion within the player and send the analog signal to the receiver. That’s not really the HDMI cable’s fault, though.
In a system where the DAC in the receiver is better than the DAC in the player: HDMI delivers on the promise of using a single cable to deliver uncompromised audio and video signals, even to the most demanding devices. Some PC equipment is beginning to take advantage of this ability. We will deal with this in a coming article on PC HDMI Audio.
Finally, HDMI cables are also superior to DVI because they can carry control signals to connected devices. Consumer Electronic Control (CEC) has been included from the very beginning of HDMI in version 1.0, and improved and expanded in every version since. It’s still not perfect, but it helps. This means less frequent switching of remote controls, or fewer steps with a universal remote.
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Upgrading to HDMI
Like upgrading to DVI (described in the previous article) upgrading to HDMI is made easier with backwards compatibility. Most computer monitors and graphics cards that have an HDMI port also have a DVI port. But even if they didn’t, you could use HDMI and DVI equipment together, with the full functionality of a DVI connection, by simply using a DVI/HDMI cable or adapter.
One thing to keep in mind, however, is that HDMI is not backwards compatible with analog devices. VGA, or more accurately, D-sub (specifically DE15HD) ports can not be connected to HDMI ports with a cable or cheap adapter. Changing analog signals to digital or digital signals to analog requires a converter that needs its own separate connection to a power source. More importantly, plan on spending 200-400 USD. Finally, you won't be getting anywhere near the quality available from the HDMI monitor or source. You can probably find a mid-range digital product to replace the analog one for less than the price of the converter. And get better results doing it.
So, as we described for upgrading to DVI, you can do it one piece at a time. Unlike the difference between VGA and DVI (explained in the first article) however, HDMI isn’t an upgrade in terms of video quality; you’re just getting a smaller connector with better home theater integration potential. Also unlike DVI, HDMI hasn’t become ubiquitous yet. Insisting on HDMI equipped computer equipment will limit your selection somewhat, though it won’t necessarily increase the price.
There are relatively few graphics cards with an HDMI port, but they are spread up and down the performance and price spectrum, so you can probably find one that suits you. Monitors with HDMI are proportionally more common, but they seem to be concentrated in the mid-range, so you might have to forget about an HDMI screen if you want either the top or bottom of the market.
If you don’t see yourself using the equipment in a home theater context, don’t spend more on HDMI equipped gear. And don’t sacrifice other features you want to get it. Where all else is equal however, you may as well get HDMI’s extra functionality, just in case. If you are planning to integrate the PC and your home theater, though: definitely make an effort to find HDMI equipment.