In reply to:

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Being engineer types, we spent a little while trying to figure out what could possibly change in the audio signal that could cause a change in the apparent _height_ of a voice. Can any of you audiophiles shed some light on this one?

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I'll chime in on this one. The reason, simply, is that your ears are not round.

The main theory of why a persons ears have all the little dents and whorls and are generally asymmetrical is to do with the person's ability to locate a sound in space. The shape of the ear affects the way sound enters the ear - sound from behind you generally loses some of its high frequency components. Normally, you can tell where a sound is coming from in the horizontal plane by a combination of phase changes, timing changes, and frequency and volume alterations (as the sound travels around your head, for example). Positioning a sound in the vertical plane is done by associating various frequency responses with various 'heights'.

Now, the frequency response graph is an arcane thing, but generally, for instance, sounds coming from behind and below lose more of their high frequency components. Therefore, all other things being equal, something with boosted trebles sounds like it's coming from above. If the MP3 recording had some treble distortion, which in other points in this thread has been pointed out to be the case, it might simulate this effect.

That's my guess, anyway.

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