Howard Shore used a range of organic sounds to augment his score in Seven; sounds of the city were incorporated directly into the score. Hans Zimmer uses electronic sounds to augment his orchestral scores. In Horton Hears a Who, the music and organic sounds were done first and the animation drawn in after. Numerous other films have used organic sounds, sounds that you might find in the film without the music present, to augment the score – sounds like cars driving by, or footsteps. These sounds all have pitch, attack and duration qualities and thus can be used to enhance the experience of the viewer by tying in the music into the sounds in the film.
There are several software programs which can tie sound waves to keys on a keyboard. These tools then allow composer to “play” these sounds like they would a piano. The more advanced tools even allow pitch variance, so if the sound of the footstep is not quite the right pitch for the music you’ve composed, adjust it by a few cents (or even a few semi-tones) to get it in line with your music.
When approaching a film, look at what sounds in the film already exist, isolate them. If there is a car driving by, but is the pitch of the sound; how does it change? If that were an instrument in your orchestra, what other sounds would you put around it? Is the sound rhythmic (like footsteps); if so, does that set the tempo or just augment a more complex rhythm.
Be careful not set too much to the rhythm of the sounds as you can wind up “Mickey Mousing” the film and the music ends up sounding cartoonish. However, some synth pads underneath can provide sustain and avoid the feeling the music in timed to every action.
You can also look at the sounds of one portion of the film and see if those sounds can be altered and included in another part of your score. Care is needed to ensure these sounds don’t sound too organic or you might confuse the audience with sounds that don’t belong. Footsteps are great rhythms, but included in the wrong place can lead the audience to believe someone (unseen) is coming. When no one shows up, the film becomes confusing.
It’s also important to spend time watching other films and seeing if you can identify how the organic sounds fit with the music.