Speck Electronics X.Sum - Manual (Page 24)

Clock noise is one of the greatest enemies of the audio racks AC system. If a
computer or any microprocessor based device (most samplers and effects are)
emits or somehow couples its clock signal with the neutral or earth of its own
power cable, it will contaminate your AC system and carry the clock noise
into other equipment; almost always with undesirable results.
The AC earth connection exists to protect you, your equipment and possibly
your building from an electrical disaster. In a properly wired system, if a 120
volt AC wire were to break within your equipment's chassis, it should make
contact with the Safety Earth Wire that is connected to the chassis, and blow
the fuse or trip the circuit breaker until the problem has been corrected.
Given the same circumstances, if the AC safety ground has been defeated with
a ground lift or the AC service is incorrectly wired, the equipment's chassis
and quite possibly everything attached in that rack would be "live" with 120
volts.
In an electronics context, an earth provides a path for unwanted EMI noise to
be carried away from your audio equipment. If you disable your earth with a
ground lift or do not have a reliable earth connection, the unwanted noise
(EMI or RFI), will find an electrical path of least resistance. That will most
likely be your audio equipment and would result in unwanted buzzes or hums.
In order for any audio signal to get from “Point A” to “Point B” requires a
cable with a minimum of 2 conductors. One conductor is the hot, or high, or
whatever you are familiar with; the other conductor is the ground or common.
Additionally, all audio wires must be protected from environmental
occurrences such as EMI (Electro Magnetic Interference) and RFI (Radio
Frequency Interference) with an outer shield. An outer shield protects the 2
inner conductors from outside interference, and prevents that cable from
inducing its signal onto adjacent audio cables.
One common misconception is that the shield of a cable should act as the
common. This may be acceptable for guitar cords or semi-professional
applications, but not for professional applications. The audio signals must be
carried only by the 2 inner conductors and the shield must act only to cover
these 2 conductors without transmitting the signal from one location to
another. It is recommended that the shield be attached to the common
(ground) at one connector's end, and the shield not be connected at the other
connector's end. It is recommended that all shields be connected at the mixer
end, and the shields not be connected at the other ends (synths, effects, power
amps, etc.).
Clock noise and AC
Safety earth connection
Proper Grounding
and Shielding
Audio earth
Chapter 4 Wiring and Other 20