Usually one of the signal input terminals of an amplifier is connected to the chassis of the amplifier, i.e., it is grounded. The amplifier is then sensitive to the voltage difference between the input terminal and ground. However, in a differential amplifier, neither input terminal is grounded. Instead, the amplifier is sensitive to the voltage difference between the two inputs. Used in professional microphone preamplifier where a low-level signal has to go some distance, a differential amplifier cancels the hum induced by the proximity of the two input wires to a source of interference. In the UK, a differential amplifier is called an inverting amplifier.