A couple of things that raise questions for me:
I have heard (no pun intended) that the higher pitch of a persons voice after inhaling helium is due to the gas being less dense than air and therefore sound is traveling faster through the helium and the pitch is raised.
Also the Doppler pitch shift effect where sound waves are compressed and/or lengthened as the source or listener are moving relative to each other, think of the pitch of a car or siren approaching and then passing by. The Doppler effect also describes the colour shift caused by light frequencies of stars coming toward or going away from us and therefore a way of understanding our position relative to other bodies in the universe.
I guess that in both these instances the pitch of the sound is transformed by the speed of sound, one by the density of the medium and the other by motion of the sound source relative to the listener.
The NASA article is more about volume and fall off of frequencies rather than pitch.
