Recently I've run across several interesting examples of audio illusions that demonstrate how the ear/brain combination can be easily fooled. For example, a web page on audio paradoxes includes examples and samples of three such illusions:
Another site, which offers some CDs of auditory illusions based on the work of perceptual and cognitive psychologist Diana Deutsch, also has some fascinating audio samples to listen to (note: stereo is required for most of these):
Can you guess this mysterious melody? (WAV, 312 KB) This musical brain teaser takes the notes of a well-known tune but randomly distributes them among different octaves, illustrating how our memory of a tune relies on the relationship between notes and not just the notes alone. Here is the now easily recognizable mysterious melody unscrambled (WAV, 313 KB), with the tones all in the same octave.
The phantom words illusion (WAV, 10.5 MB) - which is simply the same two words being repeated over and over but time displaced between the left and right channel - demonstrates how easy it is to hear words and phrases that are not there, and even hear them change, as the brain attempts to make sense of the aural ambiguity. Pretty interesting effect!
There's also an example of a speech into song illusion (WAV, 2.3 MB), in which a spoken phrase, through repetition, is claimed to be heard as song. This one didn't really seem to work for me either.
Finally, if you've done much headphone listening you're probably familiar with the concept of binaural recording, the stereo recording technique that uses two microphones mounted in a dummy head to create a more realistic headphone playback listening experience. For an entertaining and instructive example of this, just plug in your headphones/earphones and enjoy a virtual haircut (below, 4:40 min)!
The YouTube video above is a convenient way to play the audio file, but if you're interested in just the MP3 file it's available here: