Many shield-wiring practices exist in the audio
industry today. The majority of available literature on
the subject prescribes clear solutions to any wiring
problem, yet problems are rampant due to inconsistent
variations on the well-documented ideal. Two clear
groups have developed on either side of a hard-to-straddle
fence — the balanced world and the unbalanced
world.
Over the years, the declining cost of professional
audio equipment has facilitated its use in more and
more home studio environments. As home studios
incorporate professional, balanced equipment into
their systems, the unbalanced and balanced worlds
collide. Home studios adding balanced equipment to
their traditionally unbalanced gear also add connectivity
problems. Professional users never consider unbalanced
gear, yet still have connectivity problems.
http://www.rane.com/pdf/ranenotes/Grounding%20and%20Shielding%20Audio%20Devices.pdf