One of the key elements in a good film is the soundtrack. In modern film making soundtracks are very complex, involving many layers of sound, meaning they require a lot of work in post production to bring it all together in the final mix.
Audio post production can be broken down into various parts. In the mix the layers of sound are usually grouped into dialogue, music and effects. These elements must be mixed individually and then together so that they blend well and so, for example, the music does not interfere with key moments of dialogue. This is usually done using a digital audio workstation (DAW) such as pro tools. In the DAW all elements of the soundtrack are mixed and can be synced up precisely with the video.
Dialogue
This is probably the most important element of the soundtrack to get right since it is mostly the dialogue which tells the story. In post production the aim is to make sure the dialogue comes through clear, without any music or effects obstructing it. The first step is check the quality of the recordings and clean them up as much as possible. A sound editor has various techniques at their disposal in order to do this such as denoising and equalisation. A denoiser (see below) will cut out unwanted hiss sounds that were recorded in with the dialogue and an EQ can then be used to boost or reduce certain frequencies for further clarity. After this, the dialogue volume may need boosting to the right level, this can be done with a limiter. Usually we want the dialogue sitting at around 65dB in the mix, with only loud sound effects and music above it.
Effects
For sound effects in film there is a lot of scope for creativity in sound design. Sound effects can be used to add atmosphere to a scene, for dramatic impact or just for simple noises like footsteps. In post production many of these sounds must be added in, sometimes with multiple layers of sound needed to create a fuller effect. For example, the sound of gunfire may ramp up the tension in a scene, but extra sounds like voices shouting and other banging noises can really give a sense of panic and commotion.
Foley recordings are used for the “everyday” sounds in the film, such as footsteps or clothes rustling. These fill in all the sounds the viewer would expect to hear, adding realism to the film. It is therefore important to record a sound that fits the action and line it up precisely with the moment on screen.
Underlying all of this will be the atmospheric effects. These are usually tailored to a place in the film. For instance, the atmosphere inside a house will be very different to outside in a field, or in a tunnel. The primary effect used to give a sense of location is reverb, as different spatial geometries cause sound to reflect in different ways. Modern production software allows us to create a huge variety of different reverb sounds so it is just a case of finding one to suit the scene. These atmospheric differences may seem subtle, but are vital to giving the viewer a sense of surroundings. When done well they should barely be noticed and should sit about 20db below the dialogue in the mix.
Music
The final element to deal with in audio post production is the music. This will usually be composed separately and just needs to be mixed in with all other elements. Music is used to convey emotion in a scene and is placed quite high in the mix, either at the level of the dialogue or louder. Although the dialogue may tell the story with words, the music will set the tone of a scene, the final piece needed to really immerse the viewer.
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