> Has anybody had any experience with using audio over cat5 baluns for
nature recording?
Paul,
CAT5 cable is optimised for high frequency digital signals. Audio
cable is optimised for analogue Audio with a high resistance to
external HF and RF interference. Both will work, but screened CAT5
cable is very expensive and generally not as flexible as mic cable.
In the past there was an email from a recordist who plugged two short
mic cables into a long quad 4 balanced line and picked up a local
AM radio station. The short cables formed a dipole antenna. This was
admittedly unlucky, but it was using a cable out of its spec. The
extra two conductors are meant to be grounded. Quad 4 is designed to
be insensitive to magnetic fields as found in studios, that's sll.
I've looked at the CAT5 adaptors and my guess is that they use
transformers. (Are they adequately mumetal screened?) I don't see any
spec for external interference or for crosstalk across the phantom
circuits. Crosstalk on CAT5 is low for digital signals because of
"random" twist pitches, but for audio you would want these twists in
whole numbers down the cable to cancel out.
I would want something like 60dB separation between mic circuits.
If you use it for talkback, add many more dBs separation. Using two
sets for phantom-on-phantom circuts is pushing the spec very hard for
high quality audio.
Another snag is if one connection breaks, you lose the lot. With
multiple cables, you will only lose one circuit and you will know
which one.
I had mains interference problems with my long screened cables coming
from corona discharges from the 11,000 volt supply line. I cured this
by insulating the outer plugs and mics and using transformers on
unbalanced mics to give a floating input with only one ground point to
avoid earth loops. With a single balanced floating line, you can
reportedly get away with using croc clips on a barbed wire fence
according to BBC mythology. :-)
Mic cable is usually made with a soft neoprene outer sheath to make it
easy to wrap, but is much more expensive than simple PVC screend twin
audio cable which is every bit as good. Some cable with conductive
rubber screening can be microphonic, producing noise when rattled
about or trodden on.
My 100 and 150 metre cables are made from a type which is meant for
permanent wiring. It cost me 50 pence (70 cents?) a metre, but needs
to be handled carefully. The best cost-effective option is PVC
sheathed braided screened twin conductor audio cable on a drum as it
tangles when cold. My drums are garden hose reels with clips screwed
on to take the XLR's.
Making up your own cables is by far the cheapest option, even if you
have to pay somoene to do the soldering.
I've got three long cable pairs which I can deploy in my own woodland,
and they feed into my bedroom. I can lie in bed listening and press
the red button if something nice comes along. :-)
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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