|An octave on a keyboard|
This is weird.
In music, an octave is a musical interval of eight tones. If musical notes are an octave apart, they sound about the same. Here's an example of notes that are an octave apart:
1) Middle C, then C, then both tones together. Listen HERE>>
Our ears hear all these notes as basically the "same" note.
But what about this musical clip? It's a well-known song, and all the notes are the correct notes, but the notes are different in octaves. Sometimes the note's an octave or two above, and sometimes the note's an octave or two below, which makes this scrambled musical clip damn difficult to decipher:
2) Here's a well-known song with the notes at different octaves. Listen HERE>>
Even if you listen a few times, it's hard to make out any kind of song. It sounds like random notes.
3) Finally, here's the song with all the notes in the same octave. Listen HERE>>
Once you know what the song is, if you listen to #2 again, maybe a few times, gradually you might begin to hear the tune. (I can hear the end of the song, but for me, the beginning is still a mess.)
This illusion is called Deutsch's Mysterious Melody>>
These samples are from the Musical Illusions and Paradoxes CD>>