Hi cut around 16k on master

Thank you! I guess that explains it.

The only thing remaining is why a cut at 15k would produce a more radio ready mix. I’m not even sure I even know what radio ready means.

They may have been considering radio transmission when cutting above 15K. Was it an old school mixer who mixed a bunch of radio hits?

FM radio cut off above 15k so it’s a cultural reference at very least. Cutting all that makes for massive phase distortion, FWIW.

Yeah, mp3 will often have this “feature”, I think it was even on mp3 bounces from pro tools i had (might have been another software conversion too) just a while ago was cut at 16k. Then it showed a low peak at around 20k. Very strange but i think this is common on mp3

Some of the mp3 quality levels have a thing built in where there's a hard cut at a given frequency but there's leeway to momentarily extend it for certain peaks. V-0 cuts off at 20K but can extend up to 22k if I recall correctly. I think 320 is the only one from the original spec that went all the way up to 22k.

(I also remember that V-0 was encoded in joint stereo vs 320 retaining the true stereo channels. All these things were a big deal way back when.)

Never on a master(i'm not a mastering guy) I use maxed out linear phase hp/lp filters on every track except kick and bass(natural phase pre ringing), they are on every single channel of my templates first plugin in series to zero out D compensation, I high pass appropriately but low pass is trickier to me because i can't hear all that high, i use the display in ProQ to see whats up there, you can easily see the weird stuff that has to go, and then i conservatively cleave off the upper stuff leaving room for the fact that i cannot hear most of that, i do believe multiple tracks with no low pass filtering create excess hf hash that i can certainly hear especially after running it through all the bells and whistles of further plugs and processing
By doing this FIRST a good portion of the successive plugins and gear i use after creates upward harmonics that fills the space i made with desired hi freq air vs hash, clean and airy up there, thats my story, i'm sticking to it, it works for me

edit; i should add that my understanding WITHOUT filtering your speakers are working to represent all the unmusical stuff above and below filtering points causing inefficiencies hash and mud, that said my mixes after filtering and before anything else feel dull AF, but if i was desert islanding it, id' want hp/lp filters over almost anything

Solution is to ditch the analog and digital processors that make the nasty high end. “Emulations” and limiters are the worse culprits. Typical early digital limiters and the ones that imitate them no matter how sophisticated they look on paper are basically downwards bit crushers with smoothed attack (some of them have lookahead without the windowed maximum smoothing so sound even worse) and sound awful. Easiest solution is to get rid of them. Others have too long lookaheads so randomly ramp down past events based on the future and others are distortion devices or clippers. Some that aren’t and work pretty well are the limiter 6 ge (best peak limiter. Zippy to clean to soft depending on how you set it), stealth limiter (best maximizer that is like a bus comp into a limiter but it does change the sound and mix a bit), ursa boost rev b (insane upwards distorted to pumpy limiter, cleaner but pumpier than the stealth limiter, less top end lost than tdr in multiband but it is pumpier and you can make it zip bass more on faster lookahead/attacks. I tend to think it is not as good as the other two but it is a cool effect and is the loudness king now).

The multiband stuff will all defeat your mix doing anything real off. So will the too long lookahead stuff. They will undo your eq and fader moves.