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Join Date: Sep 2000
Location: Los Angeles, CA
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The most important characteristic of a (long) SPDIF cable is that it is 75ohms impedance. SPDIF running at 48K is essentially NTSC video bandwidth. 3.072 mbs, which requires at least a 6mhz -3db point. At these frequencies any cable becomes a transmission line that must be impedance matched. Otherwise reflections result and with a digital signal, once they reach the 50% signal voltage, you will induce errors.
Now all that said for a simple 6 foot connection between a DVD player and a receiver, any old analog audio cable will probably work just fine. The effects of impedance mismatch and capacitance as outlined earlier are cumulative with cable length. At short enough distances that can be ignored. Now how about an old analog cable for 6 feet at 192khz? That might be a problem!
While it's a good idea to use a 75ohm cable for SPDIF, don't get caught up in the 75ohm connector BS you read about in audiophile magazines! Connector impedance is not relevant at any standard digital audio sampling rate. The physical length of the connector is too short to have any detrimental effect. Note that in the days of analog NTSC video, BNC connectors and patch bays were 50ohms using 75ohm cable. It simply didn't matter at 6 to10mhz and the RF industry did require 50ohm connectors so that's what was widely stocked.
Now when digital video came about in the 1990s at 143 and 270mbs, the connector length now became a factor and 75ohm BNC connectors were highly recommended. When HDSDI came about at 1.5gbs and now higher, precision 75ohm connectors are a requirement.
But again for digital audio, there is no need for precision 75ohm connectors, RCA or BNC.
P.S. 75ohm RCA connectors are an oxymoron! Yes Canare makes them but IMO, anybody worried about connector impedance should not be using an RCA connector in the first place!
Last edited by Glimmie; 08-15-2017 at 11:04 PM.