Question: Due to differences in air pressure, temperature, and other factors, the speed of sound varies with altitude on Earth. Does this affect the pitch of the sound in any meaningful way?

For example, if I had a tuning fork that vibrates at around 262 Hz, would I hear the same "[Middle C](https://en.wikipedia.org/wiki/Middle_c#Middle_C)" from it while standing on the shores of the [Dead Sea](https://en.wikipedia.org/wiki/Dead_sea) as I would while standing at the peak of Mount Everest - an altitude difference of 9,271 meters or 30,417 feet?

Would there be any difference at all, and would it be perceptible to the human ear at close range? Would the altitude difference affect how the sound is heard more at a distance than it would nearby? Or, am I not quite understanding properly how sound works?

Answer: 
The frequency, which controls the pitch, is the same. What varies is the wavelength in accordance with the formula $$ \lambda = \frac{v}{f} $$ where $v$ is the speed, $f$ the frequency and $\lambda$ the wavelength. I'd imagine that in thinner air the sound would be quieter, but I'm not sure by how much. The [book on sound](http://rads.stackoverflow.com/amzn/click/0486602923) was written by Rayleigh, but I haven't read it in ages.
The speed of sound depends on temperature but not on pressure. A human voice or a wind instrument will have the same pitch at higher altitude (assuming constant temperature), but a higher pitch at higher temperature. A guitar's pitch won't change measurably, because its pitch is determined by the length, tension, and mass per unit length of the strings, none of which change significantly with changes in air pressure or temperature. A tuning fork is similar to a guitar.