Quote Originally Posted by Gary C View Post
Interesting but superficial. Just because the author of this piece says ignore altitude doesn't mean he is literally correct. You ignore altitude because you are using Rho, air pressure. The reason that altitude has an effect is because of the change it has on Rho. If you have already measure Rho then the altitude that Rho is measured at is irrelevent.

If you don't have Rho, and are making a calculation, then you will need the altitude to be able to make it.

http://en.wikipedia.org/wiki/Density_of_air
Sorry, I still don't agree. I can't find any reference to pressure or density (P) being relevant to the speed of sound in air. During my training, I remember being specifically taught that is was purely dependant on temperature.
This page sums it all up quite nicely.