MoviesOnline has an interview with Ben Burtt, primarliy focussing on his new film, Wall-E, but he also discusses some of the fundamentals of sound design / sound for film.
He talks about his use of a graphics tablet to provide him with an expressive input to control sound files:
"I could reassemble the Wall-E vocals and perform it with a light pen on a tablet. You could change pitch by moving the pen or the pressure of the pen would sustain or stretch syllables or consonants and you could get an additional level of performance that way, kind of like playing a musical instrument. But that process had artifacts in it, things that made it unlike human speech, glitches you might say, things you might throw away if you were trying to convince someone it was a human voice. That’s what we liked, that electronic alias thing that went along with it, because that helped make the illusion that the sound was coming from a voice box or some kind of circuit depending on the character."
He also discusses how he likes to use real sounds when working on sci-fi / fantasy films as it helps to convince the audience that what they are hearing could actually exist:
"The world is full of sound and we found for a science fiction film like this – and others I’ve done – the idea of taking real natural sounds and imposing them into the fantasy film gives the illusion that these things are real because we kind of recognize them even though we can’t identify them specifically, but you say “Oh, it sounds like it is really a motor so I kind of believe it.” That has been the trick in these films."
All in, an interesting interview that gives you a little insight into the creative process involved in this new film and also some background info on the sound design industry in general.