Originally Posted by Targus
This is a common myth. Twisted pairs do not eliminate any noise. Differential transmitters and receivers do.
QFT. Listen to this person.
Using "balanced" cable with unbalanced source/destination equipment does not magically turn them into balanced.
The advantages of true balanced circuit is their ability to reject common mode noise. Twisted cable (such as cat5) help by ensuring any noise picked up by the cable is picked up EQUALLY by both conductors so the differential receivers can reject them better. Unbalanced receivers will just happily amplify the noise that is picked up by the balanced cable, and you will have MORE interferance that if you used the proper shielded, unbalanced signalling cable.
Now, for a practical example, I tried the Leviton S-Video over cat5. I had a problem in that every time I turned on/off my ceiling fan in the room, I had a quick "interferance" show up on the TV.
So I replaced the cat5/cat5 punchdown S-video insert, and purchased a real S-video feedthru and real twin coax S-video cable. While I noticed no picture quality change (the impednace difference between the S-video cable at 75 ohm vs. the 100 ohm impedance of the cat 5 didn't seem to affect the picture quality enough to notice), the interferance was TOTALLY eliminated.
My run was/is 35 feet total.