Use of diegetic sound
One of the most important changes in the sound of horror in the 1970s was the increased use of diegetic sound. This refers to sounds that are actually heard by the characters in the film, as opposed to non-diegetic sounds, which are added in post-production. Diegetic sound can be used to create a sense of realism and immediacy, and it can also be used to cue the audience in on what is happening when they cannot see it. For example, in the 1973 film The Exorcist, the sound of Regan's possessed voice was created by actress Linda Blair using her own voice, which was then processed electronically. This diegetic sound helped to make the possession seem more real and horrifying, and it also gave the audience a clue that something was wrong with Regan even when she was not on screen.
Use of sound effects
Another major change in the sound of horror in the 1970s was the increased use of sound effects. Sound effects can be used to create a sense of atmosphere, to build suspense, and to scare the audience. For example, in the 1975 film Jaws, the sound of the shark's approach is created by a combination of sound effects, including the use of a bullhorn and a recording of a whale call. This sound effect is extremely effective at creating a sense of dread and suspense, and it helped to make Jaws one of the most successful horror films of all time.
Music
The use of music in horror films also changed significantly in the 1970s. Filmmakers began to use more electronic music, which could create a more unsettling and atmospheric sound. This was in contrast to the more traditional use of orchestral music in earlier horror films. For example, the 1973 film The Wicker Man features a soundtrack by British progressive rock band Genesis. This soundtrack is full of dark and eerie electronic sounds, which help to create a sense of unease and foreboding.
Conclusion
The changes in the sound of horror in the 1970s had a profound impact on the horror film genre as a whole. These changes helped to create a more realistic and immersive horror experience, and they also helped to make horror films more frightening and suspenseful. As a result, the 1970s is considered one of the golden ages of horror cinema.