Chris wrote:

> What makes a "beat" different from a "difference tone"? with respect the
> only difference I see between the two is the frequency range in which they
> occur.

As Daniel has pointed out, sometimes it is the frequency of the difference
tone itself, which we may perceive as beats if it lies outside our hearing
range. In some other conditions, it may have to do with the actual
(exponential) interval size and with the general characteristics of the
intervals; and in some of these cases, even a deviation as small as 27 cents
can remarcably change them (see my last post).

Petr