Audio Cable Tips - Alesis ADAT Reference Manual

One path goes from device A to ground via the ground terminal of the three-
conductor AC power cord, but A also sees a path to ground through the shielded
cable and AC ground of device B. Because ground wires have a small amount of
resistance, small amounts of current can flow through ground and generate a voltage
along the cable shield. This signal may end up getting induced into the hot conductor.
The loop can also act like an antenna into which hum is induced, or can even pick up
radio frequencies. Furthermore, many components in a circuit connect to ground. If
that ground is "dirty" and contains noise, it might get picked up by the circuit. Ground
loops cause the most problems with high-gain circuits, since massive amplification of
even a couple millivolts of noise can give an audible signal.
Most ground loop problems can be solved by plugging all equipment into the same
grounded AC source. However, it is important to make sure that the AC source is not
overloaded and is properly rated to handle the gear plugged into it.
For really tough cases, you may need to break the connection that causes the loop
condition. One way to do this is to simply break the shield of the shielded audio
cable at some point, usually by disconnecting it from ground at one jack. (The other
end should remain connected so that the shielding properties are retained, even if
there is no direct path for ground.)
Please note that not all hums and buzzes are caused by ground loops; your cables
must be of very high quality, particularly with -10 dBV setups. Refer to section 2.1 for
more information.
2.1

AUDIO CABLE TIPS

The connections between ADAT and your studio are your music's lifeline, so use
only high quality cables. These should be low-capacitance shielded cables with a
stranded (not solid) internal conductor and low-resistance shield. Although quality
cables cost more, they do make a difference. Route cables to ADAT correctly by
observing the following precautions.
Do not bundle audio cables with AC power cords.
Avoid running audio cables near sources of electromagnetic interference.
Do not place cables where they can be stepped on. Although stepping on a cable
may not cause immediate damage, it can compress the insulation between the
center conductor and shield (thus degrading performance) or reduce the cable's
reliability.
Avoid twisting the cable or having it make sharp turns.