My game scores have frequently featured sounds (that began life as SFX or designed sounds) being pressed into service as musical devices. I'm working on such a score right now, so it's a good time to blog about it.
In atmospheric or ambient scores, it's fun to take sounds you might hear in the game's atmosphere and time or tune them so they become music. For those of you who haven't already integrated this into your work, here are some basic ideas for heightening your score's sense of place with sound effects.
In one score from last year for a game set aboard an abandoned space ship, I took my musical inspiration from Clint Mansell's gentle, moody score for the feature film Moon. To add local atmosphere I took sounds of big, empty ocean-going ships creaking, and tuned them so the creaks began on the tonic note of a given chord and twisted themselves into half-tone dissonances. The result sounded as if the chord was being pried apart: a hair-raising effect.
Another good use of SFX we've probably all tried is replacing percussion elements with noises. A thousand TV commercials have used the gimmick, usually replacing the entire drum kit with the sounds of the client's product. (I'll admit sheepishly that I've done few of them.) This technique works best (well, to my ear anyway) when it's used sparingly, to replace just one or two pieces of a percussion ensemble. I scored a casual mobile game a few years back in the popular "cooking/time management" mold, and end up using a blend of "real" instruments (a bright tacked piano and bass guitar) and 8-bit synth tones and bleeps. To heighten the kitchen atmosphere, I built a custom drum kit that used the "hiss" of a homemade sample of butter hitting a hot skillet in place of an open hi-hat. The sound got used frequently, as the drum part was a jazzy shuffle, and the Hat of Butter gave the score a subtle kitchen-yness.
Finally, you can reinforce the track's rhythm section by stretching or squeezing existing rhythmic SFX to fit your piece. In a track I'm working on now, I'm using the sound of a steam train’s characteristic "clack-it-a-clack-it-a" to reinforce the 3-against-4 feel of the understated bass line. The train fits the atmosphere of the game, the occasional crossing whistle sounds distant and cool, and it subtly helps nail down the rhythm for the listener (in a suite where one of the stated goals is to use no drums at all.)
Scoring a shoot-em-up usually requires that you stay out of the way of the game's own SFX. But when you're working in a relatively low-energy sonic atmosphere, it's big fun to grab some SFX and make them sing.