The universal interface of the HDTV era: the HDMI cable.

The consumer-electronics sector has been forced to switch to HDMI as a result of the movie studios' insistence on copy protection - there are simply no alternatives. On the other hand, however, HDMI is also the best connection type for all high-definition formats. By keeping the signal digital throughout, even just the absence of digital-analog and analog-digital conversion results in a significant increase in quality - noise and loss of contrast are things of the past. The signal retains its original pixel raster, and therefore also its original sharpness. The highest resolution, 1080p, is only possible via HDMI, and only HDMI allows judder-free 24p playback.

But are all HDMI cables equal? No! We differentiate between two classes, which are also known as "Category 1" and "Category 2", or "Standard" and "High Speed". In most cases, Category 1 is sufficient for 1080i signals even over medium distances - and therefore also for 1080p/24, since this actually has a slightly lower, not higher, bandwidth. Nevertheless, it is recommended that you use a Category 2 cable for distances of over five meters. In general, these will easily work at lengths of up to 10 meters; at 15 meters, on the other hand, problems can begin to occur if the transmission is purely passive. At such distances, it's a good idea to use active transmission (with amplifiers/repeaters).

But it would be short-sighted to concentrate solely on the cable for HDMI transmissions; the transmitting and receiving devices also play a part in error-free connections. On the one hand, the output power isn't always identical; on the other hand, many receiving devices have special chips for restoring disrupted signals. If HDMI transmission works without errors, then the transmission is almost guaranteed to be of decent quality. The picture quality will only suffer if the signal is made to cover too-large distances, and the transmission therefore starts to reach its limits - then, for example, you might see occasional drop-outs, spots, or lines. At this point, you know it's time to consider using shorter transmission distances or better cables.

Of course, it's not only the picture that's evolving in leaps and bounds - new audio systems have also been created. With HDTV, these are Dolby Digital Plus and HE-AAC, both of which are designed for lower bit rates than those of normal Dolby sound from a DVD. This causes no problems whatsoever in terms of connections, since the receiver converts the signals to 5.1-channel sound (generally Dolby Digital) - in comparison to classical digital transmission, therefore, nothing has changed.

The situation is different with Blu-ray discs, since these use two new standards - Dolby TrueHD and DTS-HD. Both allow very high bandwidths and therefore require new types of connections. Here, two types of cable come into question: firstly, of course, HDMI; secondly, the analog variety, with six or eight cinch connections from the Blu-ray player to a 5.1- or 7.1-channel input on the receiver.

It doesn't matter whether the HD audio track arrives at the receiver as a bitstream or a PCM signal; although bitstream transmission was first introduced in HDMI version 1.3, it doesn't need a cable that matches that specification. This is because every HDMI connection provides space for audio signals - if and how this space is used is irrelevant to the cable. Even the oldest HDMI cables transmit audio bitstream data according to version 1.3 - after all, PCM audio holds more data than bitstream does.

How much should cables cost?

Cables can cost a lot of cash - in fact, you should spend about 10 percent of your total budget on them.

Maybe you've already heard this rule of thumb: Invest around 10 percent of the price of the system in cables. This rule still applies, even if some people will shudder at the thought of it. Ten percent?! That could turn into a lot of cash! But while the hardware - the TV or player, that is - is getting cheaper all the time, the prices for high-quality cables have stayed largely constant.

Furthermore, HDMI represents a new category of cable on the market, and can be massively expensive. It sounds odd to spend a couple of hundred on a Blu-ray player and then another 70 on an HDMI cable - is the relationship still correct here? Well, not exactly, but this kind of expenditure can still fall within the ten-percent rule, and it's all basically a question of length. The total budget for cables - both analog and digital - should be distributed in a way that avoids cutting corners on the most-decisive cables in terms of quality.

If, for example, you've got a high-end projector hanging on the ceiling, you'll need a long cable - maybe even 10 or 15 meters - from the player to the projector. It'll pay to spend a lot on it, since this cable is carrying a crucial signal, and the longer the HDMI cable, the more likely it is to reach the critical distance. If there's an AV receiver connected in-between the devices, consider both stretches of cable carefully (from player to receiver and from receiver to projector). Although it's possible to spend a lot less and get the same results, a total price of 100 GBP is probably realistic, whereby the short cable from the player to the receiver can - and, indeed, should be - significantly cheaper than the long cable connecting the projector.

You'll need to spend more per meter on the long cable to guarantee the same transmission quality. And this is exactly the point: Both cables - long and short - should produce the same ultimate quality. Our example is for a top projector, perhaps costing a few thousand pounds. For a flat-panel TV standing a few meters away from the AV receiver, you'll be able to get away with spending much less - just keep the ten-percent rule in the back of your mind.

Of course, you'll also need to figure in a budget for speaker cables, since these often cover large distances - and the sound also relies on the cables maintaining the signal-quality. But the ten-percent rule isn't always valid: If you have a higher-quality AV receiver that can convert all signals to HDMI, you won't need to buy additional YUV and S-Video cables for connecting to the screen.

Transmitting HD audio separately

Some Blu-ray players, such as the Denon DVD-A1UD, can relay uncompressed HD audio via analog 7.1-channel outputs.

HDMI transmits audio and video in one cable, but other HD connections require a separate audio connection. If you want to use the HD audio tracks on a Blu-ray disc, the player's analog 5.1 or 7.1 outputs are the only alternatives to HDMI.

If the HDMI connection only doesn't work because of the TV, it's possible to transmit the HDMI audio signal to the AV receiver via HDMI, while the picture comes via YUV (more about YUV a little later). But this approach often fails because most players cannot produce two full-resolution video signals at once; and, since HDMI requires the digital audio to be accompanied by a video signal, you cannot use this connection purely for audio signals.