[sdiy] Cable preferences for rig wiring looms ?

[rsdio at audiobanshee.com]

On Mar 28, 2015, at 7:41 AM, Hugh Blemings <hugh at blemings.org> wrote:
> I'm interested in conventional wisdom around good cable choices for making up custom MIDI and (line level) balanced audio leads.  Said leads will then be bundled/sleeved to make a wiring loom for my live rig to aid quick setup/tear down.
> 
> Belden 1804a seems a common choice, but it's unclear if the star-quad configuration really accomplishes much at line level ? I assume for MIDI it's of no benefit.
> 
> Keeping the outside diameter of the cable to 5mm or less is desirable to reduce bulk and weight when sleeving I think.
> 
> Would be interested in folks experience :)

Hi Hugh,

The requirements for MIDI and audio will be entirely different.

Star-quad is probably still a good choice for any balanced signal, whether microphone or line level, because power lines and other electromagnetic interference sources will affect both the positive and negative signals more equally, and thus will be canceled out more completely at the input. Star-quad keeps the geometric center of both signals in effectively the same place, and since EMI varies with distance, you want your balanced signal halves to be the same. Besides avoiding grounding issues, the whole point of balanced is noise immunity; I wouldn't diminish that to save some money just because you're running line level. Besides, if you buy star-quad in bulk, you'll always have use for it.

As for MIDI, I've used the cheapest, thinnest 2-conductor plus shield (or drain) that I can find and it still worked fine with long runs. MIDI is a current loop, so it's basically not going to pick up any noise. You just need to make sure the cable resistance isn't too high. Shielding is not terribly important to protect MIDI from noise, but it might help prevent the MIDI signals from radiating into other cables and components.

I'd recommend sourcing two kinds of cables; one for balanced audio (star-quad) and one for MIDI (cheap as hell, but covering the basics). It's your choice whether to get shielded for the MIDI or not, but if someone else has specific experience with MIDI shielding then I'd be interested to hear about that as well.

It's been a while since I ordered cable, so I don't have Belden numbers off hand.

Brian Willoughby