David Edis-Bates (October 2007) How to choose the right cables for hdtv – advice for distributors and re-sellers!




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Unravel the differences between Cables for HDTV

David Edis-Bates (October 2007)

How to choose the right cables for HDTV – advice for distributors and re-sellers!

Just because they have a high-definition cable or satellite box, or a Blu-ray Disc player, does not mean that customers can watch TV in beautiful, vivid 1080p resolution. The full signal from a satellite box or from Blu-ray Discs, does not necessarily get transferred to the television. HDTV cables are needed. Why? older cables were quite ample for transferring video at the old standard of 480i. Higher resolutions need more bandwidth, and that is where HDTV cables come in.

There are several options to choose from. DVI, HDMI and component video cables, although the latter is slowly being phased out in favor of HDMI. They can all transmit 1080p content, but the way they do it is slightly different. HDMI cables transmit the data all in one stream, while component video cables split the picture into three streams: red, green, and blue pictures which help split the bandwidth requirements up. Together, those three RGB pictures are pieced back together by the television to form the picture you actually see.



Component Video

DVI

DVI is an acronym for Digital Visual Interface and carries uncompressed digital video date to a display. When these cables first came on the market in 1999, they were primarily used for connecting the computer monitor to the PC, but today, these cables are now used for television set connection especially flat screen TVs. DVI connector

There are three different connection types with DVI cables. DVI-D refers to digital cable, DVI-A is for analog television and DVI-I is the one you need if you have both digital and analog.

HDMI

HDMI is an acronym for high definition multimedia interface. This is a newer form of cable introduced in 2002 to coincide with the introduction of high definition television.



HDMI connector

The HDMI cable is an all-digital video interface cable that can transmit uncompressed streams of data. This cable carries both audio and video signals.

It's a medium-sized 19-pin connection that's becoming standard on a range of audio-visual products. For TV, DVD and game playing it takes over the function of the Europe-wide SCART socket by carrying sound and pictures simultaneously. Unlike the SCART, HDMI uses digital signals throughout. It can also replace separate digital audio connections, such as optical or coaxial leads. In theory this makes an Audio Visual system simpler to link together.

Like its name suggests, HDMI can deliver high definition pictures and multi-channel digital soundtracks. It can also carry some standard definition formats, which is useful in the case of HDTV receivers, because not all programmes are shown in HD or with 5.1 surround sound.

HDMI is also used by 'up-scaling' DVD players, which take standard DVDs and use digital processing to produce an HDTV-like output. These players can cost as little as US$120, so even if users don't get HDTV broadcasts or own an HD DVD or Blu-ray disc player, they can still benefit from HDMI.

The TV will also need an HDMI input - preferably more than one to allow for additional items at a later date. If there are not enough HDMI inputs, switch-boxes are available for connecting more than one HDMI product and swapping between them. One, two or more HDMI inputs are now standard on most new flat-panel LCD and plasma TVs as well as rear-projection TVs and standalone video projectors.

HDMI Input

Does HDMI always mean better quality?

Having HDMI does not guarantee that the product can show genuine HDTV (at least 720 progressively scanned lines or 1080 interlaced lines) because some displays convert to a lower native resolution. The 'HD Ready' logo confirms HDTV compatibility.

Similarly, using HDMI does not guarantee a better performance. In the majority of situations HDMI provides a superior result when compared to analogue connections such as S-Video, RGB and component video, but some standard definition digital TV channels or DVDs can look worse when “spewed” digitally onto a big “high-res” screen, especially if heavy compression is used (it would be wise to switch temporarily to analogue component video). However, with more HD broadcasts and discs becoming available, poor quality older pictures should become a thing of the past.

Are there different versions of HDMI?

Yes, like the humble USB ports on a PC, there are different standards of HDMI. As with USB, products using newer standards of HDMI can be plugged together and are 'backwards compatible' with earlier versions of HDMI, so users shouldn't be left facing a blank screen and silent speakers.

The HDMI specification is currently (early 2008) at version 1.3. This offers a few optional enhancements over older versions, notably more accurate colour reproduction, faster frame rates and lip-sync correction to prevent that 'loose lipped' problem that happens when the sound runs out of step with the image.

To take advantage of the new features source machines and TV or projector must all be fully compatible with the latest HDMI version. This also includes any surround sound amp or receiver that might be connected via HDMI in the system. Products with HDMI v1.3 are becoming more widely available during 2008, such as Sony's PlayStation 3 and Toshiba's HD-XE1 HD DVD player.

Only a few current HD-ready TVs will accept the new features that come with HDMI v1.3 and, to date, just a small number of amps and receivers are fully compatible but that will change in the coming months. Good quality cabling is also important to take full advantage of the increased bandwidth of v1.3.

HDMI will continue to develop, including a possible 29-pin variation of the socket.



Are HDMI cables all the same?

It's well established that better quality cabling can minimise signal loss and distortion in the analogue domain, both in sound and picture. Although digital systems are generally more robust due to technologies such as error correction, signals can still be influenced by variations in the quality of the cable or affected by interference.



Higher grade HDMI cables are especially important for carrying the highest resolution video, which uses 1080 progressively scanned lines, also known as 1080p, but in the future products could increase this to 1440p. To connect across a long distance - to a ceiling-mounted projector for example - then a high-performance cable is essential.



About the Author
David Edis-Bates, a chartered communications engineer has spent more than 30 years in export related activities around the world, lived in Taiwan for 4 years in the 70’s and in China for the past 4 years. Currently CEO Edis Trading (HK) Limited http://www.edistrading.hk

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