Sound Audio is key when editing, using added music and sound effects will help build suspense. Exaggerated diegetic sound will allow tension to be created in the film. Fast and loud non diegetic sound can add to making the audience jump or feel scared. For example the music in the shower scene in Psycho. From this scene you can see the effect in which the sound has on the film, as without it it would be a lot less effective. Hitchcock was dogmatic about the dramatic functions of sound and music, and often interwove his suggestions into the screenplay. Hitchcock uses instruments that accentuated tension, fear and death but also that reflected the sound and movement of the knife/attack this full fills the expectations of a thriller that is supposed to be tense. For Psycho, Bernard Hermann was to concoct nothing less than a cello and violin masterwork, "black and white" music that throbbed sonorously as often as it gnawed at the nerve endings. The score would prove to be a summation of all of Hermann's previous scores for Hitchcock's films, conveying as it did the sense of the abyss that is the human psyche, dread, longing, regret in short, the wellsprings of the Hitchcock universe. According to Stefano, Hitchcock was particularly amused by Hermann's screaming violins" and "gave him more credit than anyone else he ever spoke of". This shows how important good sound was to Hitchcock who was trying to create a particular type pf tension in his thriller and slasher horror films.
Another example of sound in a thriller film is Jaws. The Jaws score is famous for the two-note signature that signals the shark’s arrival. Williams’ music makes a huge difference in Jaws. But so does the sound of water lapping against a clanging buoy. In that first scene, all the noises—musical and atmospheric—create a sense of isolation well before the low pulse of strings creep in. And even prior to Chrissie diving into the ocean and becoming shark chow, she’s sitting around a bonfire with friends, enveloped by the sound of aimless conversation, acoustic guitar, and crackling firewood—which itself sets a tone, establishing what she’s about to leave behind forever.
The sound in both clips builds tension however the most tension occurs in the moments of silence when all can be heard is the lapping of the water. The sound used in the film is imperative to build tension within the audience.