Articles and whitepapers

A Whitepaper - When it comes to HDMI/DVI connectivity, you have two choices: Copper or Fibre Optics. Which is right for you? (4/9/2006)

By Minsoo Park, Dtrovision

As digital displays become more popular, and as more people understand that a DVI or HDMI 'pure digital' connection delivers the best picture quality available today, the decision of which type of cable to use is challenging and requires thoughtful consideration.

Today's video installations grow ever more complex, with source components positioned a good distance away from the display. The distance is the biggest factor in determining which technology to use.

There are two choices when it comes to choosing the technology for your connection cable. Copper or fibre optic. This subject has been debated since the introduction of optical and coax digital audio connections and it is believed that both are comparable, that choosing one over the other does not affect the audio quality. This is true for low-bandwidth audio, especially when the distance is short. However, a full-motion uncompressed digital video signal is a different story. Due to the nature of digital signals and impedance of copper, fibre optic conversion technology is the best connection medium for DVI and HDMI signal extension.

Eye Pattern Test showing the difference on a scope between copper and fibre on HD 1080p content at 33ft. If there is no eye, there is no picture.

Fortunately, with digital video, both technologies use the same connector type. The DVI/HDMI digital signals are both high-speed and high-bandwidth. Typically, a 1080p signal would mean 1920x1080 pixels refreshing over 40 times per second. At this high rate of speed and large bandwidth of data, impedance caused by copper begins to cause signal loss - which results in digital artefacts, pixilation and/or no picture (blue screen) - if the distance is longer than 15ft. 720p and 1080i are better off with fibre optic connections if the distance is longer than 25ft.

As for fibre optic conversion technology, there is theoretically zero impedance and thus zero loss since the digital electrical signal is converted into lightwaves at the video source and the signal travels in light form until it reaches the display and is reconverted into digital electrical signals. Be sure to note the difference between 'boosters' and true optical conversion technology if you want to make sure all the pixels reach your display. Boosters used over copper wire merely amplify the electrical signal to make it 'stronger' to minimize signal loss. However, the biggest problem with this technique is that when the signal is amplified, bad data also gets amplified at the same time which results in amplified digital noise and/or pixel loss.

Another problem is that even with the boosters, the DVI and HDMI signals can only travel up to about 60ft before the signal needs to be re-boosted. This is not only inefficient;, it can be very costly.

Fibre optic conversion technology actually converts the electrical signal into lightwaves and thus maintains the integrity of the signal data up to 495ft. This is the very reason why IT infrastructures and cable TV companies are upgrading their networks to fibre optic. Considering the fact that the bandwidth of IT communication (generally less than 0.6Gb/s) is much lower than uncompressed video data (1.65Gb/s), it is easy to understand why fibre optic is better when it comes to high-bandwidth digital signals.

In addition to the copper versus fibre optic decision, here are a few more issues you should always consider when choosing the connectivity solution that's right for you:

1. Distance
If you must use copper cable, stay within 25ft. If you need to go over 25ft, go with fibre optic cable.

2. Future-proof
Connectivity products such as cables are one investment you will need to live with for at least 10 years. Consider it an investment as cable quality does make a difference and it will stay with your system for a very long time. Your current AV system may only do 720p or 1080i and a copper cable may work. However, as digital video technology is changing rapidly, you may be upgrading your DVD player or TV in the near future and you want to make sure your cables will work with your new system (especially, if you are burying the cables in the wall). Buy a cable that is guaranteed to work at 1080p.

3. Test
It is always important to test your cable before your installation. Make sure to check the return policy with the merchant before making a purchase. You don't want to run the cable under the floor or inside the wall and find out the cable is not working out for your system. Test your new cable for at least a few hours.

4. Cost
Moving HDMI/DVI broadcasts in pure digital form throughout the home is not cheap, even over copper cables. Once you go over 30ft, if using copper, you need a booster amplifier approximately every 30ft to maintain the signal. At 60ft from source to display, it can easily cost US$500 to US$800 to be done right using copper, and even then, there are some who question whether all the data and pixels will arrive properly at the display.

Optical conversion is required if using fibre optic cables. The transmitter/receiver modules go at each end of the video chain, increasing the cost more than a booster would. At 60ft, in fibre optics, it can cost US$900 for DVI and US$1600 for HDMI, roughly double the cost of using copper. However, the quality of the transmission is clearly superior to copper and represents the state-of-the-art at this time.

Minsoo Park is the President and Founder of Dtrovision LLC, manufacturer of the PureLink brand HDMI and DVI digital connectivity products.

www.purelinkav.com