How does gravity affect sound waves?

OK, I'll make my comment into an answer.

The Wikipedia article has basic information .

Sound waves are pressure waves and depend on density so gravity which stratifies the atmospheric density affects sound waves through that.

In solids and liquids to the extent that gravity stratifies them it will change the behaviour of sound waves.

Any configuration that can take density variations should have the possibility of sound waves propagating, so there could be sound waves in neutron stars.