Max wrote:

> To my understanding, difference tone is a tone, i.e. periodical
> changes of air pressure. For instance, combinational tones (due only
> to some nonlinear effect involved in production, transmission or
> perception of sound) of two frequencies "a" and "b" are frequencies
> a-b and a+b, and they are tones as well. With combinational tones
> you actually see the two new frequencies to appear in the spectrum,
> a difference tone and a sum tone, and their intensity relative to
> the source tones depends on volume.

Then you are not talking about combination tones. Combination tones do not appear themselves in the spectrum and you don’t see them in FFT analysis. If they, for any reason, eventually do appear in the spectrum, then they are not combination tones anymore.

Petr