Tell me I'm not tweaking... I noticed on this mornings dawg walk that climbing planes from O'Hare sounded comparatively hifi. Even from definitely a few thousand feet up you could hear tarmac-style turbine whine, yk that more shrill sound, echoing loudly off of adjacent apartment buildings quite literally the way it sounds in a terminal.
I actually had a hard time finding them because the higher frequency sounds making it farther down are ofc coming when the plane is directly above you, which my monkey brain was not computing properly with how loud the sound was. Even with a clear sky, I just wasn't looking for hoes that far up and was therefore surprised when I realized.
Ig I'm just shocked that if it's as simple as cold air = denser = transmits delicate high frequency sound waves better, that it makes such a massive difference between say 20° and -9° compared to 20° and 80°.