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'Totally [OT]'
2000\04\07@011724 by Rich Leggitt

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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

2000\04\07@014706 by Sean Breheny

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Rich,

I do think that there is a psycho-acoustic relationship between pitch and
amplitude, however I thought that it was that changing pitch made the
amplitude seem to change. I don't know about the reverse.

Another thing that might be happening (more likely, IMO) is that there is
significantly less low-frequency coupling between your headphones and your
ears/head when they are removed from your head. i.e., the path from
headphones thru air to your ear acts like a high-pass filter, possibly
making music sound tinny. I have noticed this with headphones plugged into
my CD player, for example.

I don't know how well this would work, considering all the stange
non-linear encoding which MP3 does, but you could try making an MP3 of a
pure sine wave and then trying this experiment again. If there is only a
change in loudness, then the answer is that the headphones need to be on
your head to effectively transmit low tones. If you still hear a change in
pitch, something else may be going on.

Sean



At 10:15 PM 4/6/00 -0700, you wrote:
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| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
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