Speck Electronics LiLo - Manual (Page 37)

If a patchbay is utilized in your mixing system, the rules for shielding change.
With a patchbay, normally all shields are connected at the patchbay jacks, and
not connected at the mixer or external audio equipment.
The occurrence of EMI (Electro Magnetic Interference) and RFI (Radio
Frequency Interference) in a contemporary studio system should be of great
concern and not overlooked when installing the LiLo. EMI is defined as any
unwanted signal which adversely affects the operation of the LiLO or your
audio system.
Stated simply, the undesirable effects of EMI may be perceived as a low
frequency smooth sounding 60Hz hum; a low frequency "edgy" sounding
120Hz buzz; or a higher frequency "whine" caused by the timing circuits in
microprocessor based devices.
Almost every electronic device generates some amount of EMI emissions.
These emissions can be transmitted as electromagnetic radiation or simply
conducted though audio cables and power cords. In the same respect, most
electronic devices are also very susceptible to the EMI emissions generated by
other electronic devices.
There are natural and man made sources of EMI that you can't do anything
about. These sources include radio, TV, and radar transmitters, as well as
motors, lights, and computers. Even the Sun and atmospheric conditions can
be contributors to noise that you experience in your audio system.
There are generally 3 elements that must be present for EMI to exist. These
include the source of the EMI (conducted or radiated), the propagation
medium by which EMI is transmitted (directly on the cables or through the
air), and the receptor that suffers the adverse affects of EMI. If any of these 3
elements are eliminated or reduced, the EMI interference will be eliminated or
reduced.
The more electronic equipment operating within a studio or equipment rack,
the higher the EMI emissions. The more audio cable and low level audio
equipment that exists within the same proximity, the greater possibility of
unwanted noise. The result of EMI in an audio system manifests itself as a
buzz, hum, whine, or all three.
The most common EMI occurrence in an audio system is radiated
emissions from microprocessors in computers, samplers, and magnetic field
sources from transformers and power supplies.
EMI and RFI
Sources of EMI
Reducing EMI
Chapter 4 Wiring and Other 33