What’s inside that coax cable, and what do I need to know about it? Is it an SDI signal, with ones and zeros heading down the cable? Is it an analog signal, with smooth waveforms traveling back and forth? There are certain key differences, one of which is the “cliff.” With analog, if you lengthen the cable, adding more resistance, the signal level gets progressively worse and worse — but it’s still visible. Now, take the same length of coax, plug it into the output of a digital media server and connect a digital monitor at the other end. Here, as you lengthen the cable, the signal remains pristine — after all, weak ones and zeros are still ones and zeros. However, at a certain point, lovingly called the “cliff,” the SDI signal vanishes. In fact, your image will start to sparkle the last foot or so, and about a millimeter beyond that, it’s toast.
—Paul Berliner, from Video World, PLSN, April 2009
