Sound designer Phil Michalski is doing a solid for filmmakers everywhere by unleashing his sonic creations on the world at zero cost to the downloader. In a Reddit thread announcing his latest package called SciFi Mechanics, he tries to make at least one SFX library available every month. If you've got a genre film in need of some sound design, be sure to check out his site.
While a few of the libraries do cost a small sum (we're talking under $3 here), there are a number of neat little options that are one hundred percent free to use. These include the aforementioned Sci-Fi Mechanics, Disturbing Booms, Disturbing Drones, Cinematic Soundscapes and Mini UI. Of course, you have the option to donate to Michalski as well.
Michalski, who conceives, records and designs all his sound effects had this tip to give aspiring sound designers: "Good field recordings are crucial. When it comes to designing SFX for sci-fi stuff you want them to be as clean as possible. When it comes to sound design itself, I recommend stacking, granular synthesis and morphing. Check out SoundToys plugins, SoundParticles and some of Waves Plugins—all of those can pack a lot of punch and character to your SFXs. One more thing—EQ. Always go for a sonic balance; you don't want your SFXs to be sound muddy or ear piercing.