Maximum unbalanced cable lengths

[bh00]

Hi,

 

I'm trying to run S-Video and composite video around a set for a production and would like to know how far standard shielded cable would carry it before it degrades the signal. I'm also going to have to run audio leads between a computer FOH and one backstage. Standard line out to line in 3.5mm extension leads. Would these reach 15-20m without degradation?

 

Thanks

[marky]

The video should be fine over that distance...

[JPSTechie]

We have run video feeds for about 30-40 meters and have had no quality problems.

[bruce]

As said above, the video should be fine - with decent cable, we've run composite over hundreds of metres, or occasionally a couple of kilometers. Needed an adjustablen launch amp and a bit of tweaking, but was perfectly useable.

 

With regard to the audio leads - theory says it's not adviseable to run unbalanced cables this sort of distance, especially the thin lo-grade stuff you usually find used with 3.5mm jacks. But try it and see - you might get lucky. I know of several installations where there are 40m unbalanced line-level connections which work fine. I also know of some where even very short unbalanced cables are problematic.

[bh00]

Ok, I'll get some long video cables. Audio wise, the first soundcard has an S/PDIF output in the form of an optical connection - is there any converter to turn this into the 3.5mm stereo jacks or have 3 of them for 5.1 output? The Creative DDTS-100 looks like it'd do the job but seems expensive and hard to found, if a little over the top as well.

 

Thanks

[Just Some Bloke]

You could just use a short unbalanced cable from the analogue outs into a DI box (or 2 for stereo) and then run mic cables for the long distnace. You should have no problem at all over that distance and a stereo DI box costs a lot less than a DAC.

[bh00]

Thing is I'd need soem sort of unbalancer at the other end to convert it back to unbalanced audio for the input to the other computer as I'm not connecting the computer to the mixing desk, but it's got to go into the other computer's line in.

[paulears]

computer to computer? Depending on if you have proper sound cards boths ends, you might get away with it, but 3.5mm plugs rather than proper connections suggests it may not be as simple as that. Assuming you are going stereo then you'll probably get a little crosstalk down the cable, but it's unlikely to be much. Try it and see!

 

What exactly are you doing? Sound a little 'unusual'.

[p.k.roberts]

A couple of issues with the audio that might cause problems; unbalanced cables are more prone to interference from other devices and you might also get hum from earth loops. Performance spaces are usually filled with bits of gear which can cause problems; from dimmers to beer coolers! Even if a system appears OK when tested, if conditions change later, 'nasties' can appear.

As a cheapish solution, our friends at Behringer make a little box containing two transformers and TRS jacks in and out (the HD400). It's only fifteen quid and one either end, with the appropriate adaptor cables might save you a lot of grief later on.

[Peter Chivers]

I'll second the last reply (as I write!) suggesting using two DI boxes, one at each end with appropriate adaptors. Please remember to make sure that these are passive DI boxes - in a situation linking two computers there is unlikely to be 48 volt phantom power available, and even if the DI box could be run off batteries, would you want to rely on batteries...

[slim_mcslim]

the DI box could be run off batteries, would you want to rely on batteries...

 

only to run every radio microphone in every show ever done!!!

 

and the battery in a DI box should last weeks turned on....

[Cougar]

Yes but a number of DI boxes (Behringer is the first to spring to mind but I am sure not the only ones) are designed so as you can use a battery but are nearly impossible to remove them again. So check that you can get the batteries out before you rely on possibly haveing to change them quicky if something does go wrong.

[paulears]

Two DIs back to back leads to an awful loss of signal, requiring lots of desk gain - line level down to mic level and then back. The improtant bit is to see how much loss the box actually has - some, even on the 0db setting have a fairly low mic level output from a hot line level input. If you do need to use one 'the wrong way' I've had more success with the cheaper ones.

[gnomatron]

You can get a cheap behringer mixer for the same price as a couple of cheap di boxes; it would probably be enough to sort out the other end of the run before it gets into the computer. Won't be a very good mixer for the price, obviously, but it would basically work.

[p.k.roberts]

Just for clarity, the gizmo I suggested is NOT a pair of DI boxes, it's a couple of transformers in a box (so not designed to do level/impedence matching), so should do the job.