pfarrell;309965 Wrote: > Anne wrote: > > What makes a cable "digital" ? > > Marketing. > All cable sends a voltage down the wire. >
Ummmm...... There's a little more to it than this, as I suspect you know. Your argument that all cables are analog is true, and I don't think anybody would be surprised to hear that the marketing types don't really understand the engineering issues, but we can at least enlighten folks on those issues! All cables have an electrical characteristic, which can be measured, called their characteristic impedance. Without getting too technical, it has to do with the size of the wires, the dielectric constant of the insulators, and the spacing of the wires, and any ground shield. At high frequencies, these factors determine the losses in the cable, and the efficiency of power transfer. Maintaining a constant impedance is also important, because where ever the impedance changes, you get reflections of the signal occurring, which causes distortion of the wave forms, and potentially, dare I say the horrid word, jitter! The transmission standard for SPDIF, over coax, was set at a characteristic impedance of 75 ohms, so a cable to be used for SPDIF should maintain this spec. Some marketing types have come to call any cable with a characteristic impedance of 75 ohms a "digital" cable. It's not strictly accurate, but when have marketing types ever really worried about the truth? In fact, a lot of the SPDIF cables out there aren't really built to a 75 ohm impedance. The RCA connector, for example, isn't really designed with this in mind. That's the chief technical argument for the BNC connector. Cheers, Dave -- DCtoDaylight Audiophile wish list: Zero Distortion, Infinite Signal to Noise Ratio, and a Bandwidth from DC to Daylight ------------------------------------------------------------------------ DCtoDaylight's Profile: http://forums.slimdevices.com/member.php?userid=7284 View this thread: http://forums.slimdevices.com/showthread.php?t=48461 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
