A particular type of free content, or a particular subclass of data sets.
Freesound the incredible collaborative sample/field recording community
FSI language courses are US-government-developed English-[insert politically-sensitive language here] courses in the public domain.
Free from any hint of modern pedagogical best-practice.
Impulse Response libraries
Libraries of reverbs, that may be convolved with a signal to make it sound like it was recorded somewhere else - e.g. record a sound in a church then play back other sounds as if they were played in the church. Aside: there is an interesting deconvolution problem in making these things, and possibly an even more interesting one in synthesising them.
Sources, via, e.g. sidebrain:
- The Echo Thief – A professor at UCSD who travels the world and record real places
- EMES Virtual Rooms – Offer Free IRs on the bottom left of the screen
- Adventure Kid – Spring IRs
- Rekkerd Impulse Response Blog – Articles and posts about convolution sound design
- Fokke Van Saane – A lot of really unique IRs. Make sure you download the Wav version of the packs.
- Lexicon 480L – Beautifully sounds IRs from the famous Reverb Unit.
- SIR ships with some examples
- Boss GT-8 – IR from the Hardware unit
- CKSDE – Separated IR Downloads
- dubbhism Stonerverbs
- Diego Stocco’s majestic mutant wierdverbs
- OpenAIR (UK-based sampled IRs)
- freeverb lists some more
- Noisevault Studio and Convolution Forums
- Voxengo Pristine Space
- Voxengo Free reverb
- echochamber’s impulse responses
- Interruptor’s music - Club Simulation
- Prosoniq Impulse Reponse Download
- K7 Sounds
- signaltonoize.com Impulse Sets
- Auditorium Measurement
- Open Impulse Response Library
- freesound IR
And ultimately anything can be treated as an impulse response; although you might have to do some fancy footwork to make it sound ok - see above re: deconvolution.