Explanation of the Shepard tone [descending]: http://music.tutsplus.com/tutorials/sound-design-falling-forever-the-shepard-tone–audio-10219
Example of the Shepard tone [ascending]: https://www.youtube.com/watch?v=BzNzgsAE4F0
Freesound Audio File: http://freesound.org/people/calivintage/sounds/95701/
Also check out my original Shepard engine and more of my sound design work on my vimeo and sound cloud here:
Apologies for the watermark throughout this video – this is my first tutorial and I didn’t want to buy a whole new piece of software so I’m using a demo and didn’t realise this would show up.