When connecting audio cables between two different AC-powered devices (i.e., computer and VCR), one sometimes encounters a low-frequency hum caused by a so-called ground loop.
This product, a short stereo RCA patch cable with a transformer capsule in-line, electrically isolates the two connected audio devices, sending only the desired audio information by inducting it between two transformers.
Radio Shack Ground Loop Isolator Model: 270-054
I've had one of these for years, and just loaned it to a friend to address a hum problem he's having connecting his USB turntable's line-level outputs to his audio receiver. I've used it in the past to connect various audio devices to computer audio inputs - a frequent source of ground loop troubles. Audio quality is good, though I've not critically evaluated the difference between this isolator cable and a straight patch cable. In every case, it was a matter of either accepting whatever impact this transformer might have on the audio or having completely unusable audio with 60Hz hum.
If you have a ground loop problem, this is the way to address the problem.