Garbage in, garbage out is certainly a thing to contemplate but if the MP3 is not the 90kbps line in got it off napster/limewire/shareaza/allofmp3 demo track (delete as appropriate) and instead something vaguely sensible (128 works for some things but we can go with 190 for this) is it really that noticeable, especially on standard human ear possibly addled by years of concerts, power tools and engines*? Furthermore does that much really matter -- jazz appreciation hour where we spend it contemplating choice of blue notes or classical where I just absolutely have to hear the pin drop during the drop (a sparrow farting outside the venue ruining the experience) not really describing the majority of musical enjoyment, even among those that would sit down and listen to music as a thing rather than allowing ninjas to sneak up while jogging or as background noise to prevent them from thinking (or thinking too much). This also says nothing of the loudness wars and effects there (from where I sit the only non mastering related benefit of the 24 bit sample depth for human audio).
*I tested mine somewhat recently. I top out around 13KHz** and it is a struggle/better if on-off testing rather than continuous climb for a long while before then (and that is with decent headphones and superb speakers in a quiet room, did it in a workshop on crap speakers and oh dear where the youths there did fine I guess), or more generally I probably have the hearing of a 90 year old. Mine started bad and only went downhill from there though (also not taking care of it in the slightest -- tools, engines, concerts all day long with no sign of PPE save where health and safety might actually cause me trouble, which is nowhere I have done anything/am self employed) so maybe understanding the plight of the golden ears is beyond me.
**
https://fretsuccess.com/wp-content/uploads/2019/03/2-all-instruments-freq-range.jpg
https://fretsuccess.com/what-are-the-guitar-string-frequencies/
*I tested mine somewhat recently. I top out around 13KHz** and it is a struggle/better if on-off testing rather than continuous climb for a long while before then (and that is with decent headphones and superb speakers in a quiet room, did it in a workshop on crap speakers and oh dear where the youths there did fine I guess), or more generally I probably have the hearing of a 90 year old. Mine started bad and only went downhill from there though (also not taking care of it in the slightest -- tools, engines, concerts all day long with no sign of PPE save where health and safety might actually cause me trouble, which is nowhere I have done anything/am self employed) so maybe understanding the plight of the golden ears is beyond me.
**
https://fretsuccess.com/wp-content/uploads/2019/03/2-all-instruments-freq-range.jpg
https://fretsuccess.com/what-are-the-guitar-string-frequencies/
Or others 
