Every encoder has a lowpass filter, not just Xing.

Duh.

I am well aware that all encoders have a lowpass due to high frequencies being more expensive per bit to reproduce. What I said was that Xing's is particularly famous for being set too low, so that the lowpass effect was very audible, and it wasn't configurable. You don't have to be a dog to be able to hear a 16 Khz signal. As I said, Xing may have taken corrective measures, but that was always a common complaint of Xing users.