Expressed in ohms, impedance contains both resistance and reactance. Microphone cables are common line level signal carriers. Electrostatic sparks or spiking from motors, neon, fluorescent lighting and other sources can become coupled onto the cables causing noise. Electrostatic charges are most disturbing on microphone or line signals because they are often amplified. Shielded cables or protective conduit provide an acceptable solution to electrostatic noise in many instances.
Capacitance changes between inner conductors or conductors and the shield can cause interference.
This internally produced noise is best corrected by using a cable with a stable dielectric insulating material. A tightly braided shield is also recommended to keep outside interference from entering the cable. Standard shielded cables do not offer enough protection. Using twisted conductors on a balanced line, several different types of conduit or armor raceways can effectively eliminate this type of noise. Depending on the level of interference, shielded cables or conduit offer excellent protection against this common noise interference.