The Austrian horror film "Goodnight Mommy" is disturbing, slow, moody, and beautifully shot and Olga Neuwirth's dense, atmospheric score underscores the unsettling feeling throughout it.
The score is used very sparingly at first, it comes into more abundant play during the latter half of the film, which makes sense since "Goodnight Mommy" is basically a one hour 40 minute crescendo. Reverb-soaked atmospheres adorn the picture in outdoor environments, adding to the vast feeling of the cornfields and forests that surround the house that most of the film is set in. Inside the house we're confined, claustrophobic - strange, out of focus photographs are on the walls. Though the house is large it feels cramped; and when we're inside it the music reflects the cramped feeling. The score is almost exclusively atmosphere; melodies don't really appear out of the haze.
There's a lot of effective sound design outside of Neuwirth's excellent score - the tried and true "not quite in tune distant piano played by a child" is used well here, as well as children singing a lullaby in unison. The kind of stuff that seems to work every time. What sounds like it may be a glass armonica plays a baroque piece in one scene; I didn't recognize it, it may be Neuwirth's own or it could just as easily be from the actual baroque era. (A glass armonica is an instrument that produces a sound similar to running your finger over the edge of a wine glass; obviously the mechanics of it are more sophisticated than that. It could also just be a church organ on the flute setting.)
For more on Severin Fiala and Veronika Franz great horror film, read this great AV Club piece on it. Or better yet just watch the movie with no expectations. It's streaming on Amazon Prime now.