A common misconception is that HDMI cables are digital cables. Wrong, wrong, wrong! Although the signal being sent are representation of 0 and 1, the signal itself is still analog in square wave formation. The longer the cable and/or the worse the cable, the square wave will deform making the delta voltage between the peak and trough of the signal closer and closer together. When the delta are too small, error correction kicks in…and any type of error correction is merely a guessing game (regardless how intelligent the algorithm) thus degrading the picture quality.
an A/B comparison of a good signal pass-through vs bad signal pass-through (courtesy of HDMI.org)
So, are expensive cables are better than the more affordable ones? NO! However. a properly shielded cable with excellent termination and connector ends WILL yield a better result than a cheaply made ones (and I’ve seen cables costing hundreds of dollars for 6ft yet were manufactured in a cheap fashion – so price is NOT the indicator).
Are better manufactured cables will make the signal better? NO! Cables are passive products, they can only pass the signal. At best, they will pass the signal faithfully. Sadly, there are too many cables out there that even at 3ft, degrades the picture quality albeit the signal is (mistakenly considered as) digital.