So I'm building this MP3 player, and I'm listening to the music through
headphones.

Then I take the headphones off and hold them away so that I can still
faintly hear the music. And the strangest thing -- there's a very dramatic
drop in apparent musical pitch. I put the headphones back on, and the
pitch goes back up. I take them off again and the pitch goes down again.

Now, I don't think the frequency is actually changing (unless perhaps the
bulb in the refrigerator is also staying on.)

But I'm wondering what's going on? Is this a known phenomenon, i.e. large
changes in apparent amplitude and/or apparent bandwidth translated by some
psycho-acoustic process into changes in apparent frequency?

Or perhaps I AM the psycho in 'psycho-acoustic'? :)

-- Rich