Even if you buy into this theory, how is this cheaper or better than using batteries to power your gear?
I also remember hearing back in the day of some audiophiles powering their systems with regenerating UPS from APC (like the kind you'd see in a data center), though PS Audio has been making such units marketed for audiophiles for a while now too.
If only there was a genre of music called “deep cycle” we’d be on the gravy train for life. (Ref: HHGG)
Visible stepping on a "pure sine wave" inverter: ¹ https://m.youtube.com/watch?v=7-Issb89NhQ&t=7m20s
Some datacenters have these attached to their generators to avoid the need for huge battery banks. They can actually support several megawatts. They spin constantly at the motor's rpm with a clutch that engaged when the input power is lost. This instantly jump starts the generator, at the grid's phase, and prevents
A cocktail of capacitors could do the trick.
Ironically, the word "battery" was originally used by Benjamin Franklin to refer to a bank capacitors, not to chemical cells.
The voltage of the grid will fall MUCH less when you pull current.
The AC voltage is rectified and smoothed with a relatively big capacitor. There is a ripple in the DC voltage because the AC can only charge the capacitor in the part of the AC cycle when the varying voltage is higher than the voltage level on the capacitor. If you charge an equal size capacitor from a big battery there will be ripple due to the inner resistance of the battery, but much less ripple because the battery voltage is always higher than the capacitor voltage. Other things equal the battery will give a smoother DC to the amplifier.
Anyway ripple is not the problem in question here. The problem is various noise from the grid finding its way through the transformer and further into the amplifier. There is very little noise from a battery compared to the grid.