Creating a good horror soundtrack is one of the most difficult tasks a composer can accomplish. Films are designed to manipulate the emotions of the viewer. Getting them scared is not an easy task.
The score needs to work in tandem with the images being seen on screen. The highest rated horror films reviewed by the Guardian all have a soundtrack that builds up tension effectively. Before a big scare, the viewer first has to feel a sense of suspense. Knowing when to make tension mount and when to cause a jolt are skills that all 
good composers need.
Perhaps the most iconic horror film score is Psycho. Bernard Herrmann created the erratic soundtrack which features high pitched violins. During the infamous shower scene, Herrmann’s violins perfectly capture the shock of a murder.
Other times a horror score can be melodic. A good example is A Nightmare On Elm Street. The theme song uses a catchy but eerie piano tune. This was later repeated in several of the sequels of this popular franchise. The best scores are ones that the audience will remember long after they have left the cinema.