A long time ago, in a galaxy far, far away, when I was just ten years old, a movie came along that shaped my future.

It was Who Framed Roger Rabbit, and for the first time ever, like everyone else in that cinema, I was mesmerised by cartoon characters interacting with humans on film.

But unlike most of the audience, it wasn't the amazing visual experience that inspired me, it was the sound. Cartoon 'boings' and comedy 'splats' were seamlessly mixed together with everyday noises and magical music. I was hooked, and from that moment on destined to work in the film business.

In those faraway days (well, 1988), sound was recorded on huge 35mm magnetic tape machines that used noise reduction to suppress the tape hiss. Twenty years later, I'm a film sound consultant for Dolby in a rapidly-evolving industry where movie directors can now carry around their entire film's soundtrack on a single, pocket-sized hard drive. But, even though technology has progressed and film sound keeps achieving new heights, the basics of the soundtrack live on...

The holy trinity

A movie's sound is always split into at least three parts; dialogue, music, and effects. For larger budget films there may also be Foley (human-made sounds such as footsteps and door slams), and atmospheres. A different team is responsible for each of these aspects, and there is a re-recording mixer whose job it is to bring the whole film's sound together.

As for the dialogue, it isn't as simple as it, er, sounds. A sync track will have been recorded at the time of shooting the scene. This could consist of a boom mic and a close mic recording, and may well be contaminated with external sounds such as camera noise, wind machine noise, and rain. So scenes which are deemed to have dialogue recordings that are not up to scratch are then 'looped' and an ADR (Automated Dialogue Replacement) track recorded.

The actors are called into a studio and the scene is looped on a screen while they recreate their vocal performances. These new tracks are then seamlessly mixed into the final version so that no one is any the wiser – unless you know what to listen for. In my experience around 99 per cent of English and American films employ ADR (it's a fairly cheap process).

Take 2

ADR is also used when a director wishes to re-script or add a line and can't go back to re-shoot the scene. For a great example of this have a look at Vantage Point, recently released on DVD and Blu-ray.

During the scene under the bridge at about 1 hour 12 minutes, Enrique's lines, 'What brother?' and 'It looks like we've both been set up,' were added during editing to completely change the context and motivation of the character. Around 30-40 per cent of Vantage Point is ADR, with the re-recording mixer (Jamie Roden) doing an excellent job of controlling the dialogues on such a busy and complicated mix.

Effects tracks open up another facet of the mix – sound design. Sound designers are a very talented breed who create sounds by manipulating other audio elements. Can we record King Kong roaring? Of course not. Well, we'll have to create it then. By running a stock noise of a lion roar backwards, at a slow speed, at a lower octave and layering multiple versions on top of each other, sound designer Murray Spivack was able to create the ape's growl for the 1933 classic movie.

The heat is on

Foley is an area of sound that sometimes gets overlooked, because if it's done well it blends into the scene perfectly. When watching any film, chances are that very few of the footsteps, clothing sounds, or punches were actually recorded live.

They were re-performed by Foley artists in studios full of props and pits, containing all sorts of materials and textures such as pebbles, melons, and raw meat. Next time you're about to cook a chicken breast or a steak, punch it and listen to the noise it makes – sound familiar? It's the classic punch sound.

For some of the best Foley effects in modern cinema check out Casino Royale. There is fantastic detail in the mix that few films manage to match. If you have the BD select Chapter nine (Chapter 14 if you have the DVD). From the bathroom scene to the card game, this is a great example of how it should be done.

What an atmosphere

Atmospheres are 5.1 tracks of atmospheric sounds. When filming a scene the sound recordist (think John Travolta in Brian De Palma's Blow Out) may well record a 5.1 or stereo track of the background noise of the location that they are using while they set up. This may then be incorporated into the sound during dubbing to give a more real-life feel to the scene. Other films will just use library atmospheres of interiors, birds tweeting in gardens, savannah sounds, rain forests, car noises, etc.

In the olden days of 35mm mag, the mixer used to have three or four loops of mono atmospheres that would play continuously up faders on the desk. They may have had a garden atmosphere, an interior, a night-time scene etc, and would just open the fader when they were required. They'd repeat every 20 seconds or so, because that's how long the loop of the film was, but no one would ever notice.

Nowadays, atmospheres are recorded as 5.1. If not, they are stereos that are split into 5.1 surround using reverbs or delays to make the them sound 'real'.

Finishing touches

While these separate parts are being honed and refined, the re-recording mixer pulls all the aspects of the mix together. He or she has a cornucopia of tools available to them on the dubbing stage and they must use them to the full to get the best from the tracks.

When the soundtrack is deemed to be in good shape the film enters the 'final mix' stage. This can be an intense period where each member of the team works up to 100 hours a week as the deadline approaches. Notes are continually coming from the film's director and producers; issues such as artistic differences, mixing desk automation problems and even picture edits play their part.

There are times when I cringe at bad ADR or hear things that stick out like a sore thumb. But there are also times when I hear something so phenomenal that it gives me goose bumps. The last time it happened was during the mastering of The Chronicles of Narnia: Prince Caspian in the scene where Lucy Pevensie walks through the forest being enveloped by the magical leaves.

The music, atmospheres and effects are so beautifully fitted together in the mix that you know that all the hard work of the sound department was worthwhile (the team on that film had been working seven days a week for six months, mind). Have a listen to it when it comes out on disc later this year – film sound rarely gets better than this.

So, the next time you put on a film and break out the popcorn, spare a thought for the guys and girls who have toiled night and day to entertain your ears.

There's a lot more to a movie's sound than just setting up a mic and pressing record!

First published in Home Cinema Choice 160