May 2005

Digital Video Connections

Having recently received for review a DVD player with a digital video output, I thought it would be a good opportunity to discuss digital video connections. High-definition-ready televisions constitute one of the fastest-selling product categories in consumer electronics. But looking at the multiple audio/video connections on the rear panel of one of these units can be confusing.

While most people will be content to hook up their DVD players with the familiar analog composite, component, or S-video connections, there are now new types of digital video connections that can provide you with an even better picture. These digital video outputs can be found on some DVD players, digital cable and satellite TV boxes, computer videocards, and other high-quality digital video sources.

The new standard: HDMI

Although the specifications for the High-Definition Multimedia Interface, or HDMI, are still evolving, since about 2004 it has become the standard digital-video transmission interface for consumer-electronics products. As the "Multimedia" in its name suggests, HDMI allows the high-speed transmission of uncompressed digital video and audio signals through a single cable, and looks as if it will become the standard method of connecting digital audio/video sources with receivers, processors, and video monitors. Although most current HDMI-capable products can transmit only two channels of PCM audio, future implementations of HDMI should allow transmission of multichannel audio, including high-resolution MLP (DVD-Audio) digital bitstreams.

DVI: precursor to HDMI

Up until a few years ago, the most common way to transmit digital video signals between consumer-electronics products was via Digital Video Interface (DVI) connections. Like HDMI, DVI is an uncompressed digital video interface; unlike HDMI, it doesn’t transmit audio signals. A few years ago, it was common for HD-ready televisions and some high-end DVD players to have DVI inputs and outputs. Although a few current products still support DVI, more and more new products use HDMI exclusively.

HDMI/DVI compatibility

What if you have an HD-ready TV with a DVI input and a new DVD player with an HDMI output? The good news is that HDMI is back-compatible with DVI: You can connect an HDMI-equipped device to a DVI-capable device, and vice versa. However, because one of the devices supports only DVI, audio signals will not be transmitted. This will require an adapter to convert an HDMI connector to a DVI connector, or a cable with an HDMI connector on one end and a DVI connector on the other. These adapters and cables are a little harder to find than regular HDMI or DVI cables, but they’re available from a number of high-quality cable manufacturers.

HDCP encryption

A major part of the specifications for the latest digital formats -- DVD-Video, DVD-Audio, SACD, Blu-ray, and HD DVD -- has been encryption of the digital signals so that they cannot easily be copied. The content-protection scheme used with HDMI and, optionally, with DVI is called High-bandwidth Digital Content Protection, or HDCP. If you’ve purchased a DVD player or other device that outputs DVI or HDMI, it probably came with a warning that its digital video output would be compatible only with a display device that supports HDCP. This is probably not a major problem; all HDMI devices support HDCP, and most DVI-equipped consumer TV sets also support it.

IEEE 1394 (FireWire): compressed video and audio

Another digital video and audio interface is IEEE 1394, aka FireWire or iLink. Although it’s been around for several years, IEEE 1394 didn’t catch on in the audio/video industry, presumably because it compresses the digital signals, which could theoretically lead to a loss of picture and sound quality. It also requires additional processing to decompress the signals once they’re received. One of the advantages of IEEE 1394 is that it’s designed as a two-way protocol -- through it, different components can "talk" to each other. This means that a component’s operation could conceivably be controlled through its IEEE 1394 connection.

IEEE 1394 is somewhat more common in the computer industry, although far less so than the ubiquitous USB interface. One place you can probably expect to continue to see IEEE 1394 is in high-end processors, receivers, and universal A/V and SACD players. This is because it is one of the few interfaces that allows the transmission of high-resolution digital audio from SACD.

To further complicate matters, there are two types of IEEE 1394 connectors: six-pin and four-pin. Fortunately, the two types are compatible with each other -- you just have to make sure you have the right one on either end of your cable. The four-pin connector, more common on A/V gear, is often called iLink; the terms FireWire and IEEE 1394 can be used interchangeably.

Do I need a digital video interface?

If you’re purchasing a video device with a digital video and/or audio interface, and unless you have a need for one of the other interfaces to connect to another piece of equipment you already own, make sure the new component has HDMI capability, as this seems to be the current standard.

If you own video devices with digital video interfaces, you should consider investing in one of these new digital cables. They can be relatively expensive, but you should be able to buy less expensive, generic IEEE 1394 cables and even DVI cables from a computer supply store. Just make sure you get a DVI-D cable, the type used by nearly all consumer televisions, and not a DVI-I or DVI-A cable. And remember to get IEEE 1394 cables that have connectors with the correct pin configuration for your components.

HDMI cables are typically available only from specialty cable manufacturers. If you don’t have a local dealer, a good place to start would be www.hdmiplanet.com. Run by the same people who manufacture BetterCables, HDMI Planet sells high-quality HDMI and DVI cables at factory-direct prices. Another good place is www.audioadvisor.com, which carries many digital video cables from manufacturers such as Analysis Plus, AudioQuest, and Kimber Kable.

...Roger Kanno
roger@hometheatersound.com

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