Should I take this "S/PDIF" cable back?

[bobmirror]

I just purchased a "S/PDIF" cable for $35 (20') and have A/B'd it with a decent quality instrument cable with 1/4" to RCA adapters on either end and there is no difference in sound quality. I feel like a fool for paying so much when I could spend half as much for a decent quality RCA cable and get the same results. What causes "jitter"? Any help is greatly appreciated.

-Bob

[Joe Hannigan]

Jitter can arise from a number of problems, usually lack of a master clock, or using cheap onboard clock sources with each individual digital device, instead of one master clock for every digital device in the chain. Another problem is cheap cables. How much or how little this effects the sound is arguable, but I'm one of those that feels it's best to get EVERYTHING right in the chain, so that it's a non-issue at the end.

SP/DIF info is much higher frequency-wise than analog audio signals; it's digital, and beyond the 20-20k needed for analog audio. Yes, you COULD use a generic cable in a pinch, perhaps with no audible trouble at all, but I wouldn't risk it. Jitter is one possibility, loss of actual data is another. (Clipped sounds, breakup, harsh artifacts, etc.)

Remember too, that musical instrument cables are "unbalanced" and there is measurable changes in resistance and capacitance over the length of the wire due to the way it's made (1 center conductor, 1 shield outside of the center insulator). As the length of the wire changes, so does the frequency response, and the first thing to go is the high end. (esp the VERY high end...where your digital data will be.) (Balenced cable - two conductor w/shiled can also be used for AES/EBU digital, but that's another story, another time...)

A long time ago, I once ran a 25' stereo audio cable for a SP/DIF device (DAT to Sound card I/O) and spent over two hours trouble-shooting the damn thing, wondering what was wrong with the software. Pretty funny (NOT!) when I swapped out the cables for a shorter, "video" cable and the damn thing worked fine.

Good cabling never hurts either but $35 sounds a tad steep if it's just a cable with good connectors on it. (gold plated, perhaps?) You didn't mention what type the SP/DIF cable was - a fibre optic, or a wire. (I'm assuming it's a coax cable). Twenty feet sounds a bit long, too, unless you have a real need for that length. (Are you just connecting two racked devices to each other?)

I'd be wary of 20' lengths more than the cable itself. For a 3-6' cable to interconnect with components, you're probably fine with something a little less exotic, perhaps just a good coax video cable with the right connectors. For SP/DIF, I personally WOULD get something dedicated (skip the adapters, too, if you can) instead of a generic "Musical instrument" cable.

If you can live without the $35 you spent, then keep it, coil up what you don't need, and learn from it. But definitely DON'T go "cheap" and use a musical instrument cable. In this case, what you don't know (or hear) WILL hurt you.

[tmix]

I agree 100% with Joe.
Digital cabling is an area you dont want to skimp on. You may not want to pay $100 for a cable that you can get the equivelant for $30 but down the road a bit the $30 will be a non-issue where as the audio cable could become a complete nightmare.

It is worth the price of a dinner out, to not have IT eat your lunch!

tom

[bobmirror]

Thanks for all the information Joe. I guess I'll keep the cable so that jitter stays a "non-issue" (as Tom suggests) in the future. Yeah the cable is decent Canare components with durable gold plated RCA heads. The 20' is to connect one piece of equipment on one side of the room (using a different wall socket) to my computer's soundcard on the other side of the room. I was looking for a 15' cable but couldn' t find one.

Just curious but if jitter or errors ever do occur are they always very audible/apparent?

Thanks again,

-Bob

[bombastique]

I'm not sure where you're reading these studies, but the SPDIF spec definitely states 75 ohm cables.

More here:

http://www.epanorama.net/documents/audio/spdif.html

I would be curious to read these studies you're referring to - got any links?