By the side of my earphones, there's a switch that flips between two initials, IP and NK.

[This Quora question](https://www.quora.com/What-are-IP-and-NK-transformations-in-earphones) suggests that this is the IP / NK transformation, which somehow makes the earphone universal.

What exactly is this and what is it for?

NB: I bought the earphones from China, and the manual is of very little use.