How would sound be different on a planet with a stronger gravitational field? My reasoning leads to sounds of the same wavelength having higher frequencies - is this correct?
Sounds travels faster through denser mediums.
In a planet with the same amount of air in the atmosphere, but a larger gravity, the gas would be compressed more tightly and thus be more dense at the surface.
For this reason, the velocity of sound waves would be higher.
For two waves synthesised with the same wavelength, $v = f\lambda \implies f \propto v$. So if the velocity of sound waves on the stronger-gravity planet is higher, then so are their frequencies (for a given wavelength).