I have a degree in Computer Engineering. I've designed digital logic for years.
In the old days, Analog mattered. It was a signal, that would have to be strong and clear for a good picture. That being said, going a short distance, the quality of the cable is not such a big deal. It might be if you are going to connect a projector 20` away.
Now, when you get in the digital domain, you end of quantizing or sampling an analog signal (Assuming you are going Analog to Digital). Once you go digital, its all data (1's and 0's). There are no 1.5's or 0.2's.
If you are going pure digital, like HDMI, there are only two ranges for the signal. High and Low (corresponding to 1 and 0). Therefore, as long as the device receiving the signal can sense the High and Low, you are good to go.
Don't get fooled into spending $100.00 for a 6` cable. As long as the signal gets though, it doesn't matter. You will NOT get a better picture.
I buy the least expensive cable I can find.
As others said, monoprice.com is great. I've purchased 20` HDMI cables from them and they work without a hitch.
Hope this helps,
btanoue
Hope this helps.