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.
Sources of EMI
Reducing EMI
Chapter 4
Wiring and Other
22
