[Haskell-beginners] Code review request

Hi everyone, After spending some time reading "Learn you a Haskell," I decided to try writing my first Haskell program (https://github.com/dobyrch/musicbox). It reads ASCII "sheet music" and uses the terminal bell to play the song as it displays the frequency of each note. I'm looking for any tips that would make my code look more idiomatic. Please point out any places where I could simplify the logic or use standard library functions in place of custom code. Style suggestions are also welcome--let me know if you see anything ugly that could be written in a more readable way. Thanks! Doug