S/PDIF line lengths and patch bays. Unlike the AES format, S/PDIF is a signal protocol that was never intended to be run through audio cables or audio patch bays. It’s a pure 75-ohm format and requires 75-ohm coaxial cable in order to work optimally. In many cases it is possible to use standard audio cable for S/PDIF, but it is not recommended and results can vary (sometimes subtly). Two questions (for the price of one) we get a lot are:
How long can a S/PDIF run be?
The S/PDIF specification calls for 25 feet max. No one wants to warrant longer lines for all applications. If you use good 75-ohm cable with good 75-ohm connectors you may be able to go further in some situations. Longer lines are a function of the quality of the transmitter, receiver and the impedance match for the entire line, including the connectors.
Can I run S/PDIF through my audio patch bay?
In the borrowed words of our immortal Mark Phillips, “You can fool some of the people all of the time and all of the people….” You get the idea. Again, quality of the connectors, cables, transmitting device output and receiving device input, patch bay, shielding/grounding method all play a part. It is possible for it to work. Shorter overall wire lengths equal higher probability of success. A good RF patch bay, like they use in video houses, would be better.