[codeulike]

Universal in the sense that a number of rocks or a number of sheep can be doubled just as a frequency can?

Yes thats what I meant, the doubling of frequency. It might seem trivial but the fact that doubling frequency sounds "right" to humans is actually quite interesting. Why does it sound "right"?

[sheiyei]

Interference is most of the answer. With frequencies f and 2f you get the smoothest interference patterns, even if the tones have a lot of harmonics. This applies reducingly to increasingly fractional ratios.