I am impressed by the ability of the HumBug to remove mains noise, but how does it work? A noisy waveform is the summation of two separate components. One component is the biological signal of interest and the other is noise of various forms. These forms of noise include random fluctuations generated by the sensor, amplifier and background biological noise in the vicinity of an experimental setup. The HumBug is designed to cancel electrical interference. It constructs a replica of noise embedded within the input signal and subtracts this replica from the noisy signal as it passes through the device. The end result is an output which contains only the signal of interest – mains noise removal without filtering.