Speck Electronics ASC - Manual (Page 27)

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 computeres, samplers, and magnetic
field sources from transformers and power supplies.
23
Reducing EMI
Sources of EMI
Chapter 4 Wiring and Other