optical cable length

[doug_hti]

hi, I want to extend some stuff optically. I notice there are some cables "hosa" up to 50ft. Is this a bad idea? Are there any problems with different cheaper brands and lengths of cables. I know not to create any sharp bends...and Im usually picky about my audio and AES/EBU cable, but I am just quite not up to speed on optical...

[BrianT]

Originally posted by doug_hti
hi, I want to extend some stuff optically. I notice there are some cables "hosa" up to 50ft. Is this a bad idea? Are there any problems with different cheaper brands and lengths of cables. I know not to create any sharp bends...and Im usually picky about my audio and AES/EBU cable, but I am just quite not up to speed on optical...

Yup, a 50' Hosa lightpipe is a very bad idea. It will hurt you. There are many differering opinions on this subject, as much as anything because of large variations in the quality of the optical transceivers inside the gear and the quality of the cables. People get into dogfights about lightpipe audio quality while they are using/comparing totally different hardware. Not smart.

So there's not "one" answer, as usual. But I think the following info about lightpipe is fairly universal.

1. Shorter is better, always. As in 1' is better than 3', 3' is better than 10'. So imagine 1' vs 50'.

2. Cable quality matters, obviously. But I know of no one who has actually documented differing cable quality by brand under anything approcahing scientific conditions. So we're all guessing, aren't we?

3. Using something besides the lightpipe itself for word clock is a very good idea, since much of the issue with lightpipe is the jitter induced during transmission. I'd expect using an AES line or WC coax for clock with lightpipe for data would have a big impact on many of the issues here. That is certainly the only way I use lightpipe these days.

But again, be wary of somebody who starts tossing out absolutes about "what's OK" on cable length with this many variables involved. You would have to quantify the specific gear and application first. Then actually test that in an A/B with the alternative. THAT would be a firm answer.


Regards,
Brian T