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The Audio Frontier
HDMI has been all the rage for home theater users, and for good reason. Born in 2002, HDMI was designed to be a high-quality, backwards compatible (with DVI) digital connection for use between various devices. This doesn't sound particularly exciting, but it is important, because even the connection between two devices in your living room can suffer from bandwidth issues and from degradation of signal quality. HDMI was built with new technologies, such as high-resolution televisions, in mind, and as a result it is capable of carrying, in a single cable, everything needed for high-resolution video.
But more relevant to our discussion, HDMI is also capable of carrying up to 8 channels of digital audio. All versions of HDMI have a maximum audio bandwidth was 36.86 Mbps, which is a lot. As a result, HDMI is one of the highest quality audio connections available to consumers today. This is great news for HTPC users, because it means the days of having to using DVI/HDMI connections AND a plethora of audio connections are over.
Unfortunately, there is a catch. Not all methods of connecting a PC to a receiver or HDTV using HDMI will allow audio to be transferred as well. You'll need specific hardware in order to take advantage of this feature. There are also some compatibility issues that you may need to overcome.
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What You Need
The best way to transfer sound via HDMI is, surprisingly, using your video card. After all, one of the biggest advantages of HDMI is that you do not need to have numerous audio and video connections. Recent video cards, like ATI Radeon 3xxx and 4xxx series, as well as Nvidia's 9xxx and GTX series, include the ability to output sound. And they're not bad, either - compared with some of the finest sound cards available, there is no apparent difference in quality. In addition to these video cards, many motherboards using ATI or Nvidia integrated graphics have HDMI outputs which will put out both video and audio.
If you have one of the ATI video cards or a motherboard with HDMI, then you're done. These examples do not require any special connections. Simply place your video card in your computer, install the latest Radeon drivers, and you're set. All you need to do at that point is attach a DVI-to-HDMI adapter to the DVI port on your Radeon card, and then attach the HDMI capable that runs to your home theater system.
If, however, you have a Nvidia card, there is one extra step you need to take. Nvidia's cards can output sound, but they actually require a SDPIF connection from your motherboard to your video card in order to function. In other words, you have a SDPIF cable as a physical bridge between the connection on the video card and the connection on your sound card or motherboard. Once you've done that, however, you simply attach a DVI-to-HDMI adapter to use the audio.
Note that some video cards, particularly those aimed towards HTPC users , actually take out the need for an DVI-to-HDMI adapter by including a HDMI output standard.
Once the connection has been made and the video card drivers installed, your computer should be able to output audio via HDMI without issue. But the key word is "should."
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Dealing With Driver Conflicts
The primary obstacle which prevents HDMI audio from working correctly is driver conflicts. That which is being output to a display device via HDMI doesn't run into conflict, because it is being sent out by your primary display driver. There are no other drivers that could possibly be active at that time. However, the situation is more complex with audio. Although you've installed the drivers to use HDMI audio, you'll still have your previous audio drivers installed and possibly active. And for good reason. The computer speakers do not use any kind of HDMI connection.
In a perfect world, these two kinds of audio connection would play well together, allowing you to use them simultaneously. In the real world, however, the various audio drivers on your PC will come into conflict with each other. This can happen in both Vista and XP, and it can happen with both Nvidia and ATI video cards.
Fortunately, solving the problem usually isn't difficult, and is largely the same in both Vista and XP. You will simply need to open up the Sound properties in your Control Panel, which should in turn show you a list of sound drivers currently installed. Make sure that the HDMI Output is set to enabled, and that all other drivers are set to disabled. This should solve the problem. Note, however, that you will need to close out any program that was started while the non-HDMI drivers were enabled, and restart it. For some reason, Windows does not seem to switch the audio driver a program is using while the program is still running. If your HDMI audio still is not working, then try rebooting.
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Enjoying The HDMI Experience
Once you've started using PC audio via HDMI, you'll probably never look back. The quality is as good as you'll find anywhere, and the convenience of loading your video and audio onto one connection, as opposed to using separate connections for each kind of output, is outstanding. It allows nearly any computer to be a home theater PC, at least for a few hours. In fact, the feature is so convenient that discrete sound cards seem suddenly pointless for home theater PCs. Obviously, you'll still need a sound card or motherboard sound connections if you want your computer to be able to use standard PC speakers. However, if you're building a HTPC, there are numerous home theater video cards available which integrate video and audio over HDMI, nudging the sound card out of your HTPC's limited space.