post #16 of 16
The change in altitude results in two things: a reduction in air density and a rduction in air pressure, but since the two effects virtually cancel, they can be ignored. That leaves temperature and humidity, of which temperature has the significant effect, humidity very minor.

But all of this is meaningless if you don't have a lot of air for sound to go through. Last I looked there wasn't much air between my headphones and my eardrums, even less between my IEMs and my eardrums.

If listening at high altitudes seems to sound different to you, you should look for a cause other than the air itself as the transmission medium.