The phase switch is the equivalent of swapping the red and black speaker terminals on both speakers at the same time.
It's use is controversial, as recordings, preamps, amps and DACs may or may not output in correct phase, and some listeners appear to be much more sensitive to this than others.
It's use is controversial, as recordings, preamps, amps and DACs may or may not output in correct phase, and some listeners appear to be much more sensitive to this than others.