Analysis of the use of audio codes within my media text

We use all different types of audio codes within our trailer such as music, dialogue from the camera footage, voiceovers and non-diegetic sounds.
Our music is very important to us. At this point in time we have used 3 different tracks, two of which are the same track however one has been remixed into a more upbeat and 'ravey' version of the original acoustic version we have used. ('Uninvited') We use the acousic version at the start to keep the mood calm as in the film the mood is calm and nothing is going wrong. However we have edited in the more upbeat remixed version to fit the realisation of Charlotte not being a normal girl. The audience see her change into a more obsessive girl as the music changes. This was done by editing and merging the two tracks together in Garageband. Our song at the end of the trailer 'White Blank Page' by Mumford and Sons is used as it is slow and gives an odd sense of happiness and dullness at the same time. This works well in opposition of the clips being shown while it is being played, for example, Charlotte running wildly down a coridor whilst happy gituar music is beoing played.
Our voiceovers have so far been successful as they work well in the trailer. Our first one at the beginning of the trailer when Charlotte introduces herself 'Hi, i'm new here?', 'Name?', 'Uhh...Charlotte Westbridge'. This works well as we are not using filmed footage in order to do this so it is playing over another clip therefore getting more information in within the time-span of a conventional trailer. Our second voiceover at the moment is of Summer saying 'So why did you move here in the first place?' This was done simply because when it was filmed it was not loud enough and when we made the volume louder it sounded grainy and distorted. This way it is a more clearer sound and makes the trailer look more professional. More voiceovers will be done and will work in the similar ways of the above.
At the very beginning of the clip, the audience can subtely hear the students in the classroom Charlotte is about to walk into talking. The audience wouldn't be able to make it out but it adds to the atmosphere of the situation she is in. It suggests that the people in the room are already comfortable talking with the people in there and do not want change, i.e Charlotte walking in and trying to become friends.