Speck Electronics MicPre 5.0 - Manual (Page 35)

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
MP 5.0. EMI is defined as any unwanted signal which adversely
affects the operation of the MP 5.0 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 computeres, samplers, and
magnetic field sources from transformers and power supplies.
Sources of EMI
Reducing EMI
Chapter 4 Wiring and Other 29
EMI and RFI