Why HDMI? What you need to know before going digital

updated High Definition Multimedia Interface, or HDMI, is hailed as the next generation of audiovisual cabling. Simply put, HDMI is an all-digital connector that can carry high definition video and several digital audio channels all on the one cable. HDMI was first officially unveiled in 2003, but it's only now that we're starting to see widespread support for the standard. Is it something you should be seeking out?

2. How is it different from my current analog cables?

Analog video cables, such as component, composite or S-Video, are currently the main methods used to transfer picture signals in an average home system. Component is the highest quality analog cable as it breaks down the picture signal into three different cables — one each for red, blue and green. When you've got analog cabling connecting digital sources (such as an LCD or plasma screen with a DVD), the digital video or sound signals have to be converted into analog to travel through the cable, before being re-converted back into digital at the receiving end. This could lead to some signal degradation and a resulting loss in output quality.

3. What are the advantages of going digital with HDMI?

HDMI can deliver high quality sound or vision without the risk of quality loss due to the conversion or compression of a video or audio signal. HDMI pictures should be smoother and sharper, with a distinct reduction in video noise. Sound should be crisp and taut, without any distortion. And of course, using the single cable HDMI can get rid of a lot of messy cables snaking around your home theatre kit.

Because of its digital nature, HDMI also works well with fixed-pixel displays such as LCD, plasma or DLP screens and projectors. A HDMI cable allows you to exactly match pixel-by pixel the native resolution of the screen with whatever source device you've got connected. HDMI systems will also automatically convert a picture into its most appropriate format, such as 16:9 or 4:3.

HDMI has some built-in smarts that allow you to control any device connected via HDMI through the one remote. Since the HDMI connection allows two-way communication between devices, it gives you basic universal remote-like functions which, for example, can tell the components in an HDMI-linked system to turn on when you want to watch a DVD, just with the press of a button.

4. How does DVI fit into the equation? Is it better than HDMI?

You may have heard of digital video interface (DVI), which is another all-digital connector for video. DVI has been around for longer, and can be found in many more televisions and other devices than HDMI. DVI was initially developed as a connector between PCs and monitors, but eventually found its way into the home entertainment world.

The HDMI standard is actually based on DVI, so picture quality should be identical. Where HDMI has it over DVI is its audio capabilities — DVI can only carry video signals. HDMI cables can also be made longer than DVI — HDMI can go up to 15m in length. And from an aesthetic viewpoint, HDMI connectors are less bulky than DVI ones. HDMI connects like a USB device for PCs, while DVI still has screw pins on its connector. However, this means that HDMI connections are more prone to damage from accidental knocks so more care needs to be taken with them.

5. I've got some gear with DVI connectors. Will they work with HDMI?

As HDMI is fully backwards compatible with DVI, so you won't be making your DVI products obsolete if you buy something with an HDMI connector. For example, HDMI televisions will display video received from existing DVI-equipped products, while a HDMI DVD player will play on a DVI-equipped television. All you'll need is a HDMI/DVI adaptor. Just be aware that doing this will lose you the added functionality of HDMI, such as automatic screen format conversion and universal remote control.

6. What products support HDMI?

HDMI has been on the market for a while now, and most new DVD players, set-top boxes and TVs feature at least one HDMI port.

div>

On the display side of the equation, most new screens, projectors and DVD players support the standard. If you're looking to buy a device like a TV or AV receiver look for the most HDMI ports yu can afford. Three is the minimum you should expect from today's devices, while DVD players and the like only usually require one output. Also, be aware that an HDMI port currently only sends information in one direction -- though there are moves to change this in the future. As a result, it's not possible to use a HDMI output port on a PC, for example, to display a PS3 signal.

7. Where can I get HDMI cables?

If you own a component with HDMI but don't have a cable for it, then there are several cable manufacturers who sell HDMI gear. Belkin, for example, sell HDMI cables and HDMI to DVI cables under their Pure AV range of interconnects. Monster Cable also has a comprehensive selection of HDMI products. HDMI cables and adapters by Monster Cable have been developed in a joint partnership with HDMI's founder, Silicon Image. Don't expect these cables to be too cheap, though: you'll need to spend at least $70 to get a cable of sufficient quality.

8. What do the different versions mean?

While the latest version of HDMI is up to 1.3c, but there are four main versions that most equipment will correspond to — 1.0, 1.1, 1.2 and 1.3. Notice that the versions signify changes to the types of audio they can transmit, as all versions should be able to transmit HD video up to 1080p.

1.0 This is the first version of HDMI and it was ratified in late 2002. It will decode most versions of audio contained in DVD and digital TV signals, including Dolby Digital and DTS.

1.1 This version added DVD-Audio support, which means users with compatible disks and players can listen to 5.1 channel audio streams without the need for six separate audio RCA cables.

1.2/1.2a The main improvement on 1.1 is the addition of Super Audio CD (SACD) support, which means users no longer need to rely on iLink or analog cables to listen to SACDs. The standard also adds support for an as-yet unused Type A PC connector.

1.3/1.3a/1.3b Version 1.3 adds support for Dolby TrueHD and DTS-HD Master Audio which are used in Blu-ray players. Increasingly, AV receivers are including decoding for these standards on board, while devices the PlayStation 3 will output a decoded signals. The 1.3 standard also increases the available bandwidth by a factor of two to 10Gbps. Though 1.3b and 1.3c exist they don't add any further functionality over 1.3a, and so are interchangeable.

9.What's this I hear about Wireless HDMI?

Eventually, every technology goes wireless, and with Wi-Fi and Wireless USB now in play it makes sense that manufacturers have turned their eyes to making HDMI clutter-free too. Only thing is, it doesn't work yet. Belkin showed off their FlyWire technology behind closed doors at CES 2008, and it hasn't been heard of since. There is, as yet, no standard for Wireless HDMI, and so it's not really worth holding out for. Also, Wireless HDMI is not to be confused with WirelessHD — this is a separate technology used by manufacturers such as Sony to send signals from a media box to slim, wall-mounted TVs.