The mains man

Hi-fi buffs often claim to improve sound quality with bizarre electronic
“tweaks”—but the results are often highly subjective and hard to prove.
Jean-Claude Froidevaux is filing patents around Europe (EP 859 483) on a device
which he claims improves fidelity by applying a signal to the mains supply
powering the hi-fi. Half the mains feeds the hi-fi, and the rest is used to
generate a frequency twice that of the mains. This signal is used to induce a
matching frequency in the supply. This, claims the inventor, makes the mains
supply “cleaner” and gives “improved quality” sound.