Diegetic and non diegetic sound in horror films

Diegetic sound is any sound created from a source within the world of the film. Non diegetic sound is sound that comes from outside the story.
Non diegetic sounds used in horror movies can be very effective as it can create a very eerie and suspenseful atmosphere for the audience, and diegetic sounds make scenes in the film more realistic.

This is the opening to Jaws, a very famous horror/thriller movie with an iconic soundtrack. Diegetic sound is used when there is a party. The sound of people chatting, a crackling fire, music and singing are example of this, and these certain sounds create a very relaxed, calm atmosphere, which contrasts with the horror of this opening scene, thus making it more shocking and horrific for the audience. The non diegetic soundtrack used throughout the film is used to signify when the shark is approaching. This builds suspense and indicates that danger is coming, striking feelings of fear and alarm.

Here is another iconic horror film scene- the shower scene from Psycho. This has a very different take compared to the opening of Jaws, as there is no non-diegetic music at the start, Instead, there are only the diegetic sounds of the shower curtain being pulled and the water flowing into the bath, making the scene seem very realistic, which is effective as the more realistic it is, the more scared the audience feels. Rather than having dark non diegetic music build up suspense as the killer's silhouette appears behind the curtain, there is only silence (along with the sound of water) until the curtain is pulled and the killer attacks the victim. This is where the non diegetic sound comes in, high pitched, shrieking violins with sounds of the knife plunging into the victim's body. This approach is more likely going to make the audience jump and feel shocked and alarmed.

For our film opening, we liked the idea of slowly building up tension with the use of eerie non diegetic sound. We paired this with the diegetic sound of the victim breathing, to make the scene more realistic. A lot of sound effects were used to create a larger impact on the audience, for example when the blood drops on the ground, or just after the victim gets killed. Our intention was to create the feeling of shock and fear, and our use of sound definitely helped us to succeed.