Research and Planning: Why is sound needed?

Overall I think it is sound that creates the ultimate tension within a film or a trailer. In horror trailers especially, mood music can be used to manipulate the viewer and make them believe one thing while the narrative may make them believe another. For example having a contrasting music soundtrack to a narrative may keep the viewer fully engaged within the trailer and making the climax much more effective. Other sounds including non diegetic floor boards creaking or a door creaking can increase the horror by letting the viewer know something is about to happen, increasing the anticipation as it cannot be viewed, the same effect is still created with diegetic music yet I don't think it works to its full effect. Voice overs can also be used in trailers as a way of informing the viewer what is happening throughout and also giving further hints at what will be happening within the film making the viewer want to see more. I therefore think that sound within a trailer is greatly important as a way of keeping the viewers attention and keeping them gripped.