could I use this digital cable for audio ??

[DeadPoet]

Hi y'all,

A friend of me had a batch of about 30 metres digital cable (ISDN) lying around, and gave it to me if I could use it.
It's described here, but I'm not that a technical guy.

AFAIK it's 8 x [ 2 wires with 1 ground but wrapped in aluminium] + 1 big braided shield thing.

Would this be usable for making a 8x snake with a shared ground ? I know this wouldn't be ideal, but it couldn't hurt ???

Thanks again.


Herwig

[DaveM]

I think a digital cable needs to be able to carry 75 Ohm. I didn't see this in the specs. Others may know better than I.

Of course, if it's free, then what the heck. Give it a try.

[knightfly]

First, digital cable for audio is either 75 ohm (SP/DIF) or 110 ohm balanced (AES-EBU), so this cable wouldn't be advisable for digital signals in a studio.

The crosstalk figure of 80 dB reflects the lack of individual shielding per pair. Unless you have a Behringer mixer, I wouldn't recommend it for analog either.

Also, the bend radius of 10x the diameter, means it won't go where you want it to in a cramped rack, and probably won't lay right on the floor either.

Maybe you could use it for trading stock, or beating elephants to death... Steve

[DeadPoet]

Thx for the info, will rethink the elephant-beating part (maybe if I attach my behringer mixer to one end i could use it to demolish small houses )


Herwig

[sjjohnston]

On the crosstalk: one thing that's missing is over what length that amount of crosstalk is presented. So far as I know, the standard length for such measurements in the world of interconnecting digital equipment (what this cable is built for) is 100 meters. 80 dB of crosstalk over 100m actually seems pretty darn good. If I'm interpreting the picture and description that goes with it, the pairs are separately shielded, which would explain the good crosstalk performance.

Physically, it looks like it's intended for permanent installation. As noted, it's not very "bendy" ... also the foil shields may not be a good idea for something that gets handled alot. That seems like the main limitation in using it to carry audio in a studio. If you do use it, use each pair for the two legs of a balanced line or, with an unbalanced line, use one or both wires in a pair (i.e. don't mix two unrelated signals in the same pair).

[knightfly]

SJ, your interpretation of the picture makes more sense to me now - I guess the T in PET refers to the foil shield? At first glance, I didn't think the pairs were individually shielded. If they are, and that xtalk WAS for that long a run, the stuff should be fine for non-impedance sensitive stuff like analog. (Provided it's for non-moving applications, as you noted)

Now, about those elephants... Steve

[sjjohnston]

PET is some kind of polyethelyne, I think. Aluminum can be laminated together with it to make a nice, relatively bendy foil. I think. This rapidly gets beyond what I know, or even think I know. That spec sheet at the link wasn't the clearest thing in the world, but it might show a per-pair foil and drain-wire.

[littledog]

I would think using digital cable for audio wouldn't pose nearly as severe problems as using audio cable for digital. But i admit, I haven't tried it.

[knightfly]

Hey LD, you're right - my only concern, other than the stiffness, was that the individual pairs had no shield. I'm thinking now that I mis-understood the drawing/specs, since they aren't really clear on that point.

I have gotten some of the cleanest sound thru wires EVER, by using digital cable for audio. I scored some 27 pair Belden DATA cable a few years ago for $10 per 500 feet, simply because it was worthless as salvage (too much crap, too little copper) - after checking the capacitance (11 pF per foot) I made a 120 foot snake out of part of it - The first gig I tried it on, I had to change my normalizing teqhnique of setting all High EQ's at +3, to all highs at -3. Stuff was so bright it almost took our heads off.

The rest of that spool is waiting for the new studio rewire. Any single or double runs will be 110 ohm AES cable, for the same reasons.

After measuring the cap per foot on normal audio cable, including some high rollers like mogami, I would never go the other way - some of that stuff has 30-45 picofarads/foot, not to mention the wrong characteristic impedance for digital. I'd hate to see the shape of pulse edges after going thru that stuff... Steve

[littledog]

Originally posted by knightfly

After measuring the cap per foot on normal audio cable, including some high rollers like mogami, I would never go the other way - some of that stuff has 30-45 picofarads/foot, not to mention the wrong characteristic impedance for digital. I'd hate to see the shape of pulse edges after going thru that stuff... Steve

Not only that, but when you use audio cable for digital, you actually get reflections of the signal bouncing back and forth from one end to the other. Don't ask me how or why, that's just what the heavy tech guys told me.

[sjjohnston]

Originally posted by littledog


Not only that, but when you use audio cable for digital, you actually get reflections of the signal bouncing back and forth from one end to the other. Don't ask me how or why, that's just what the heavy tech guys told me.

Yes. That's what the whole 75-ohm (or 110-ohm) spec is all about. It doesn't ordinarily matter for audio, because the wavelength is much, much longer than the cable you're running it through.

[DeadPoet]

Thanks for all the info!!

I'd like to use the cable for permanent installation until I have the dough to buy some mogami or canare snake. If I'm interpreting your answers right, it would be ok to use the 8 pairs for + and - of my balanced signal and have a common ground ??? I'm a bit worried for the ground... separate is better, but as a temp cable couldn't hurt? A P.A. guy told me it would be ok to do as long as I'd only use it for audio only (not mixing it with eg. DMX light signals)

Thanks a million

Herwig

[knightfly]

Herwig, since you have the ACTUAL cable in front of you, can you clarify whether or not there are INDIVIDUAL shields (foil, or braid) on the pairs, or just ONE overall shield? The spec sheet isn't clear on that at all.

That, for me at least, would decide whether I would even take the time to try it... Steve

[DeadPoet]

no individuals, only one.
Actually I have 8x (3 leads + 2 plastic filler threads [3a in the spec], but wrapped in aluminium foil). 2 of the 3 leads are shielded in plastic [1&2 in the spec] , the 3rd [3b]is explosed to the aluminium foil [4] , and the total of 8 pairs is in a braided shield [6].

Clear ?


Herwig

[knightfly]

At this point, I would say that if you have more time than money it would be worth trying this cable for audio. The advice against other types of signals was a good call. Whether you will have more crosstalk than you want for audio will almost have to be decided by experiment.

Other than sex, pizza, beer and playing musical instruments, there are few things I enjoy doing over and over, so I would find a way to trade for what I need, or wait. Your mileage may vary - you might get away with it depending on what that plastic is like around the individual pairs. If it's some type of conductive plastic, there could be some shielding effect.

What it comes down to is try it and see - I'm not convinced, based on what you've told us about the cable, that it's a good idea. However, everybody knows that advice is much better to GIVE than to TAKE... Steve