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Many audiophiles invest in some expensive audiograde mains cables like the Russ Andrews variety in the hope that it will improve the sound of their audio system by removing noise. These are usually simple twisted pairs which have some RFI attenuation but not much, or a screened cable which shields the mains conductors from RFI. In fact the use of screened mains leads is common practice in many computer office environments and industry running machinery. It is not something magic for the audio community only. These are a good investment but are useless on their own without some real filtering before them. The reason why is that your house or building is full of twin and earth gray mains cable. This is a standard, not 'high audio grade' cable which is buried beneath the plaster in the walls and under floor boards and pretty much covers your entire house like a giant aerial. Now a few inches of plaster and wood are not going to stop noise getting onto this from various sources. Noise generated inside the building directly onto the conductors or RFI noise again from inside and outside. This is not even taking into the consideration the many miles of cable in your area and other buildings near by on the same phase before your sub-station. So a 0.5m or 1m audio grade mains lead IS NOT going to remove any significant amount of noise at the audio end that has accumulated in the miles of cable before it reaches your system or have some magic property that compensates for the miles of standard cable laid out before it. Noise must be removed just before these types of cable are used by a proper in-line filter circuit. The filter acts like the barrier between the circuit of your house and that of your hifi.