9 ft. Optical Patch Cable Length for Pioneer DVD?

Posted by SMR [WizOp] on October 01, 1998 at 20:03:27:

In Reply to: 9 ft. Optical Patch Cable Length for Pioneer DVD? posted by Nicholas Rexing on September 17, 1998 at 20:50:58:

Nicholas,

: As an example, we know that light travels various paths through a fiber depending on the characteristics of the media, cladding, etc. and the quality if the laser. Now I'm way out of my league here, but I'm lead to believe that (depending on these characteristics) it may take several feet before there is the equivalent of an electrical leading edge that accurately represents the timing of the light pulse. If this is true and the link is short then the receiving optical-to-electrical device may have a difficult time resolving when to switch between a logic low and logic high. This would have the effect of changing the electrical pulse widths or the timing between pulses. I speculate that a long link cable has a filtering effect on the light and allows the light to, if you will, converge into a coincident wave to assure accurate conversion at the other end.

What you're theorising here is that the length of the optical cable, if it is short, does not allow the binary state to be defined clearly enough to accurately resolve the signal without jitter (differences in the timing between receiver and signal). Well, as we're discussing light pulses here, there never is going to be "the equivalent of an electrical leading edge", instead just replications of the binary notation.

What's the absolute worst thing that can happen assuming your assumption is correct? It must be the introduction of jitter, a phenomenon which is contentious to say the least. One thing we do know about jitter is that there has to be a lot of it before it becomes noticeable, and I'm willing to bet that those extra eight feet of cable will have absolutely no impact whatsoever on it's audibility.

It's also worth noting that even if all the above were true (which I still very much doubt), only PCM will be effected. Dolby Digital and DTS are transmitted as data blocks. Either enough data survives for the format to work perfectly, or enough is lost to cause a drop-out (silence). There is nothing in-between.

Interesting all the same… I think it's a typo - either that or Pioneer have a warehouse full of nine-foot long Tos-Link cables. ;-)

Stuart.

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