Question: Most audio signal are described by a curve having two parameters: The amplitude and the frequency (amount of time from positive to negative amplitude value).

What I want to understand is how the sound level and absolute pitch are encoded to these two values. How would amplitude and frequency change if I'd change volume or pitch?

Thank you in advance!

Answer: 
By definition an orbit occurs when gravity balances with the "centrifugal" force. It is essentially a **free fall** situation.

So the answer is the same reason why you don't get stuck to the ceiling of a free falling elevator. Both the spacecraft and the occupants are moving **in-sync**.
The Shuttle (or the ISS for a better example since the Shuttle isn't flying any more) **isn't** rotating at a great speed...it's rotating about once every 90 minutes, once every orbit. This does have an effect, but a very small one.

Its motion around the Earth doesn't produce any such effect because, as you guessed, it and everything in it are in free fall around Earth and are affected nearly equally by Earth's gravity (the very small differences due to different distances from Earth do produce tidal forces).