Yes (from the little I know) a major aspect in our hearing is that nature doesn't produce pure sinusoids. Mechanical vibration materials is bound to have a seri

Yes (from the little I know) a major aspect in our hearing is that nature doesn't produce pure sinusoids. Mechanical vibration materials is bound to have a series of resonances multiples of some basic frequency. So if you have a single person, or single object, emitting sound, you expect to see this nice harmonic lineup. When the fundamental frequencies don't have a pair (a,b) s.t. a * f1=b * f2, their harmonic multiples don't match and you can tell something is odd. For f2=125% f1, for example, every 4th harmonic from f2 lines up perfectly; for f2=150% f1, every 2nd harmonic lines up; for f2= 200% f1, every harmonic actually lines up. I guess it's like looking at combs with different spacings and finding ones that superpose neatly.