beats and differences

In a conversation between Doug Goncz and Ray Tomes:

>>My physics teacher told me about an article in a physics journal from back in
>>the 60's or 70's about a pehnomenon called the "ghost flute".

>Probably Scientific American. I don't think a physics journal would
>publish a paper on perception of a beat note.

>Let's say we have a flute at A440. And another at (perfect) E1320. The
>beat will be at A880, which does happen to be in the range. A beat can
>be either in or out of the range of the instruments creating it. In the
>range, it sounds corporeal. Outside the range, it sounds ethereal. I am
>stretching, but I think this is clear.

It sounds like a confusion between two different phenomena here.
There is the "beat rate" and the "difference frequency".
They are obviously closely related conceptually,
but they are most likely caused by different
perceptual mechanisms. This is discussed at length in

D. E. Hall, ``The difference between difference tones and rapid beats,"
American Journal of Physics, 49(7), pp. 632-636, July 1981

which may or may not be the article your physics teacher was
referring to.