MP3 works not by reducing dynamic range or frequency response, but by discarding data that's less likely to be heard.
< caps from the internet quote.
If one wants to hear the difference between a -let's say- a 256k MP3 and FLAC, do *not* expect to identify it by expecting to not hear the higher frequency ranges. You'll fail. If anything, the MP3 will harshen them some and make them thinner-sounding. Which is why often people think the MP3 sounds actually "better", since the detail has been flattened with the psychoacoustic model used in MP3. *Not* by reducing the frequency range.