This may turn out to be embarrassingly simple, but I have not been able to wrap my head around it. Correct me if I'm wrong, but as I understand it: A note, tone, pitch, whatever you call it, is a vibration at a frequency. In the real world they are usually complex waveforms comprised of several frequencies related mathematically. A pure wave with no complex additive frequencies sounds like a sine wave, a tuning fork, a theremin. A bass string, on the other hand, is rich with additive frequencies (overtones, harmonics) and we generally debate which brand of strings has the most pleasing set of those harmonics. Why are these other frequencies not perceived as separate notes? Why is that complex waveform not perceived as a chord? As I understand it a chord is two (or more) notes, i.e. mathematically related frequencies, vibrating at the same time. Same definition as a single note with overtones (or harmonics, or timbre, or whatever you call it). Same definition, two completely different sonic animals. Why?