A chord played on a piano is multiple different pitches, each at a different frequency, played simultaneously. The ear hears this as separate sounds. The cochlea of the ear is organized by tone (tonographic organization), from highest to lowest frequency. So a triad chord will stimulate three corresponding area of hair cells in the cochlea separately. My question is: how do the three tones get perceived that way? Why not as a single complex wave? It seems that the combined air pressure wavefront generated from three different notes actually should combine to form a very complex wave pattern, through a sort of Fourier summation. Does the ear do some kind of "reverse" Fourier analysis to break up this complex wave pattern into its individual component waves? This is even more puzzling when you listen to a whole symphony orchestra all playing together at the same time. You can still distinguish the strings from the trumpets from the tympany from the flutes from the triangle, etc... It can clearly still distinguish all the different pitches and timbres, with all their associated overtones, ranging from the tuba to the piccolo. But I can't even imagine how complex that combined wave of all these instruments would appear if you would put them all on the same graph. Somehow it seems the ear is still able to sort them out and hear them as separate sounds though. And a related question regarding the stereo diaphragm: how does a single diaphgram vibrate to recreate all those different sounds, not to mention all the overtones? It must be vibrating as the sum of all those waves, in the same way the ear drum must be vibrating. How?