On Monday, March 10, 2014 8:24:12 AM UTC-7, D. Peter Maus wrote:
On 3/9/14 23:49 , isw wrote:

In article ,

"Ralph D." wrote:

I need a cable (ideally about 20ft), stereo 3.5mm male/male, highly shielded
to connect my audio source to a transmitter across a room. This cable passes
many sources of interference, so the shielding is critical.

A more effective solution would be to convert the audio to a balanced
line at one end, and then back to unbalanced at the other. Better CMRR.
Shielded twisted pair, here, will get the job done.

Yep, this is the best solution: it takes transformers (or active-circuitry equivalents)
though, so it might be a tad hard to implement. The wiring for this kind of thing
is widely used for microphones (microphone cable and microphone connectors
solves the cable-purchase part of the problem).

I'm not sure where to buy, but searching on 'audio balun' seems appropriate.
The word 'balun' indicates a balanced-to-unbalanced transformer (and you'll need two).