Hum

Hum is a steady state, low frequency anomaly usually audible in narrow bands of one or more frequencies. A common source of hum is interference from the electric power supply.

In North America, electricity results in a 60Hz hum, as well as hums from any number of 60Hz harmonics, (120Hz, 180Hz, 240Hz, etc.). In Europe, electric power is based on a 50Hz cycle and results in a 50Hz hum and the harmonics thereof, (100Hz, 150Hz, 200Hz, etc.).