Jimster480
Headphoneus Supremus
Here is a quote from blue jeans cables on the subject in response to a question asked on their amazon listing for a 3ft coax cable:
"We have heard the notion of 1.5m being the optimal length for SPDIF, but cannot make heads or tails of the claim -- it simply doesn't make any sense at all from a technical perspective.
When it comes to how long a cable should be, we always think of the story of Abraham Lincoln being asked by two men -- one rather long-legged and the other rather short-legged -- what the best length for a man's legs was. Lincoln replied, "long enough to reach the ground." In the same way, we think the optimal length for a cable, barring some technical constraint (e.g., maximum working length), is "long enough to reach from the one device to the other." Of course, it's never a bad thing to have an extra couple of feet so that the cable isn't under any physical strain when in place, and so that equipment can be moved without damage to cables."
Well it really does depend on the quality of the cable and the amplification at the source as any signal dissipates over distance and that distance is based on resistance.
Now if it were optical it shouldn't matter the length as its fiber and doesn't really lose light across the distance of the cable.