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Schmanthony 14th August 2002 05:54 PM

TOSLink Cables All the same? Any degradation over Length?

I'm more than willing to abmit I don't know what I'm talking about... but that's the reason for my questions:

Why would I spend more $$$ for a "premium" TOSLink cable over a budget cable? Is there really going to be a difference? I mean, this is *digital* information over *fiber optic* cable... is there really going to be any signal loss whatsoever over this medium?

Why are TOSLink cables advertized as "shielded?" Shielded from what? Some even say they are RF shielded.... what? How could radio signals interfere with *light*?

Someone please set me straight, because if my understanding is correct there are a lot of marketing gimmicks and shams going on with these cables and I'm inclined to buy the cheapest cable I can find. Seems the manufacturers are exploiting consumer's expectations that these cables will suffer from the same problems affecting traditional copper wire cables that carry analog electrical signals.

This is a Home Theater/Audio issue that has always bugged me, and I've come here for an explanation.

Oh - on a related note... would the signal be adversely affected when it's running over, say 50' of TOSlink instead of 3'? I mean, wouldn't the same lossless signal make it that far undegraded? (Or am I incorrect to assume that digital TOSlink information is lossless?)


sam9 14th August 2002 08:34 PM

The only plausible thing I've read that could make a difference with toslink is that bad ones might exacerbate jitter. Jitter appearently can be measured. The only question is is it audible. I'll leave that for others.

RF shielding is IMHO like de-magnitizing CDs, manifestly silly.

Baring jitter, unless an optic cable is inducing more errors than the error corecting algoritms can deal with, they ought to all sound alike. Bits is bits.

What may be a more realistic concern is fragility. You can break the suckers. At least if this happens the effects won't me debatable you just won't get sound. Nice thing about didital it work or it doesn't (baring jitter).

BTW I bar jitter because I'm not teky enough to talk intelligently about it. I'll grant that it's been measured but it's an open issue with me still if it is audible. I doubt it, but I'm willing to consider the possability.

peranders 14th August 2002 09:13 PM

Sheilding = B***********(X) as long as it is not optical!

Every digital circuit creates noise = jitter.

How much BETTER is one particular transmission technique? I don't know.

I use TOSLINK with a very cheap nylon fiber (3 mm) and I sounds splendid together with my DAC.

BTW: TOSLINK works at least 25 meters with normal operating currents and a simple nylon fiber. The light is noticable weaker than with a short fiber.

Don't forget that many DAC's "eats" jitter, like mine. (CS8402, CS4328).

(X) I try to write "tjurskit" without the "ullshi" but even that is filtered out! OK, my mouth is filthy. I change to dumheter instead. Since we discussed language elsewere everyone understand when I write in swedish ;) .

Schmanthony 14th August 2002 09:15 PM

Hmmmm.... jitter,

All I know about that (very little) has to do with ripping audio CDs. When your CD-ROM is reading bit by bit data that is supposed to be streamed (I think...) sometimes a dirty, scratched, or warped disc is likely to cause significant distortions in the transfer process. Much more than what you would hear if the data were actually streamed (since the laser in the CD-player would just skim through it), instead your cd-rom drive in read mode is trying to read those "dirty" bits one-by-one and loses track or something.

I'd be willing to bet that jitter in CD's is usually inaudible... and the same thing would probably go for DVD audio as well. If you ever hear anything wrong at all, then it's probably *really* bad and no cable will save you from that.

It seems like the first thing to "go" on a less-than-perfect DVD is usually the picture. I've never heard the audio start crumbling before the picture does.

So you might have a point about better TOSlink cables inducing less errors, which could be additive with respect to errors coming from the reader like there might be from jitter. I kind of doubt it, though. I also have a feeling it wouldn't be economical for manufacturers to engineer different "grades" of fiber for consumer home audio. However, engineering marketing gimicks has the potential be highly economical! I think they'd just make one product that works. (Like you said, either it works or it doesn't). I'll bet that any dressing up the premium product gets is probably for sheer profit margin and nothing else.

I really want someone to tear me apart and tell me why I'm wrong. Until then I'll be buying the dirt-cheapest TOSLink cable I can, and be happy knowing I'm doing no worse than the guy who paid 3-4 times as much for that monster-gold-super-shielded-premium-deluxe malarky.


Schmanthony 14th August 2002 09:19 PM


Yeah, now that I think about it the light would get weaker further away and there would be more error in the signal.

But you think up to 25m would be OK? If so that's good for me because I only need about half that for my current project.


peranders 14th August 2002 09:26 PM

Re: 25m

Originally posted by Schmanthony

Yeah, now that I think about it the light would get weaker further away and there would be more error in the signal.

But you think up to 25m would be OK? If so that's good for me because I only need about half that for my current project.


You don't get more errors but if you attenuate the light even more it simple stops working. It's very clear when the signal is too weak. Very audioable and very easy to see on an oscillscope. You don't ones and zeros at the maner as from a bad CD. The transmission link is very "digital", it work perfect or not at all.

10 meters is the garanteed length with TOSLINK. I think the limit is around 25-35 meters with nylon. Glass fiber is better but I don't how much.

Cobra2 14th August 2002 09:56 PM

Toslink ...
I have seen "Repeaters" for extended lenghts of TosLink.
As for (glass)fibre, I work w. tools on end of kilometres of fibre... : ROV.

Arne K

Jocko Homo 15th August 2002 12:22 AM

How to make a bad idea......... this case SPDIF.........worse is to use TOSLINK. They all have poor jitter performance. ST is only marginally better because 99.9999% of them are poor implementations.

In the case of ST, a longer cable would almost certainly be an improvement.


tiroth 15th August 2002 03:43 AM

Why is longer better?

hifiZen 15th August 2002 06:30 AM

Think reflections, propogation time, and jitter.

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