A bit more detail here \ Cable "quality" hard to test with digital.
A "typical" audio cable may have a shield constructed of several bare wires wound in a spiral fashion the entire length of the cable, over an insulated center wire.
At audio frequencies, this will not matter much and will not disturb the signal greatly (better quality audio cables aren't built this way)
Digital\video\S\PDIF signals are a different thing, they cover a wide spectrum of frequencies and an audio cable with a spiral wound shield may look like a "coil" of wire instead of a direct connection, coils tend to pass low frequencies and tend to block higher ones (general assumption here).
That would mess up a signal that has a wide range of frequencies (way above audio), the longer the cable the more "scrambled" the signal might become.
Many digital systems use some type of error correction and are "happy-est" with a low rate of errors.
If a "marginal" quality cable is used, there may be digital errors introduced with-out the user knowing about it (the errors are automatically being delt with)
OK, so any cable should work right?.... MAYBE!
As the system corrects for the "cable" errors, it has less ability to correct for any additional errors (dirty disk, external noise, etc.) and the result is less "headroom" (correction ability) available.
The "good quality" cables are done with another type of shield construction, it is a "braided or woven" construction, the strands go in two directions, being interlocked as they go, leaving a flexible but more solid even construction that A)Allows the signal to flow with minimum disruption, B) Provides a solid barrier to outside noise\interference.
The result is that the "bandwidth" (low and high frequencies) is mostly flat and even with as little dips\peaks as possible, that a cheap audio cable might cause.
I used to work at a company that produced digital switching equipment, and we could "see" (using digital analyzers) the effect of a poor transmission line\cable, often if just a foot of extra cable was added, the error rate would skyrocket.
Rather than use "any chunk of cheap wire" to connect your digital devices, do this-
Use a good quality 75 Ohm cable when required by the type of signal you are carrying, this way you keep the error rates down, maintaining a good "headroom" to deal with possible "source related" errors and their correction, and keep the "digital stream" as pure and error free as possible.
Unlike analog, when you run out of correction "headroom", digital really crashes badly! (digital TV never fades to "snow", it gets "block-ey" and quits!).
Mark T.
