768 mph is average pressure speed of sound. I have no idea how fast or how high up that thing was though- But all things considered I still believe that was a sonic boom. I mean you can see the shockwave. Who in their right mind would use explosive bolts that powerful to separate a rocket from something as sensitive as a…
As far as air density is concerned I would say the speed decreases as air density increases. More distance for a molecule to travel before it hits another.
I figured people who drink beer and... orally indulge would be able to tell me if this was due to alcoholic consumption or.. over indulgence. P.s. Yah there is something wrong with my line.