Balanced Wiring
Balanced Wiring is a cabling method used to protect audio signals from noise and electromagnetic interference.
Think of two messengers carrying the same information, but in opposite directions (inverted polarity), through a noisy crowd.
Differential Signal: In a balanced cable, the audio signal is duplicated. One copy is normally sent through one conductor (hot wire), and a copy with inverted polarity ("upside down") is sent through another conductor (cold wire). These two wires are the "messengers".
Shield): The two wires are wrapped in a metallic mesh that acts as a shield, connected to ground. It captures most of the external interference, such as radio interference (RFI) or electrical hum.
Common Mode Rejection: Any noise that manages to pass through the mesh reaches the two inner wires in the same way and with the same polarity; the noise is heard equally by both wires.
Inversion on Arrival: At the destination equipment, a differential receiver subtracts one signal from the other by inverting the polarity of one of the wires. Since the noise is the same on both wires, it is canceled. Since the original audio signal has reversed polarity on one of the wires, the subtraction restores it to twice its original strength (Signal - (-Signal) = 2x Signal).
This process, called common mode rejection, makes balanced connections extremely effective at carrying low-level signals over long distances without picking up noise. It is the professional standard for connecting microphones and other equipment, using connectors such as XLR and 1/4" TRS.