Pterosaur hearing

Nothing is known about this to my knowledge, sorry Brian. The fact is that we have very few good pterosaur skulls that have not been flattened during fossilisation. Larry Witmer has done some scans of 3-D preserved skulls looking at brain shapes (since the enclosed space of the skull will reflect the shape of the brain that it housed) but he didn't look but the bones of the skull that might tell you a little about hearing were not preserved.

Right now, we don't know and can't really know without much better evidence. Even then I think it would be very hard to make a statement as broad as the one you have given - towards low or towards high. Either are viable - some pterosaurs were very small and thus probably produced high-pitched sounds, others were big and may have made deep noises. Or alternatively they could have been responding to important environmental sounds - the high piched whirring of insects flying, or deep growls of predatory dinosaurs - its pretty hard to say sadly.